Warm Season Vegetables: Can They Be Transplanted?

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Some warm season vegetable plants are sensitive to root disturbance; gardeners should plant these vegetables directly outdoors after weather warms in the spring. Other warm season vegetables make excellent candidates for seeding into small pots or containers for later transplanting.

Solanums. Solanums, including tomatoes, peppers and eggplants are not sensitive to root disturbance and are ideal candidates for transplant. Gardeners may place seeds for tomatoes, peppers and eggplants  directly into small pots for later transplanting. Of course, seeds can also be started directly outdoors when risk of frost is low and daytime spring temperature are sufficiently warm. Different vegetables have different cultural requirements, including daytime temperatures. For more complete cultural requirements of different solanums, see tomato, pepper, hot and pepper, sweet.

Cucurbits. Unlike solanums, most cucurbits, including summer squash (including zucchini), winter squash, cucumbers and melons are sensitive to any root disturbance, such as from transplanting. Surface cultivation, digging, harvesting root crops, thinning, or weeding near established plants may also cause root disturbance to cucurbits. From the time of germination onward, it’s generally best to avoid all root disturbance as much as possible for all cucurbits. Seed cucurbits directly outdoors, when daytime temperatures are sufficiently warm. For more complete cultural requirements of different cucurbits, see summer squash, winter squash, zucchini, pumpkin and cucumber.

Corn and Beans. Like cucurbits, corn and beans, both pole and bush, are sensitive to root disturbance, including from transplanting. Again, like cucurbits, seed corn and beans directly outdoors, when daytime temperatures are sufficiently warm. For more complete cultural requirements, see corn, bean, pole and bean, bush.

Early Spring Planting: 3 Ideal Vegetables

Heavy Feeders and Spring Planting

Spring Gardening: 5 Tasks You Shouldn’t Forget

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Planning Vegetable Gardens in Mediterranean Climates: 3 Common Mistakes

Planning a spring garden

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This time of year, many gardeners in California’s coastal and inland valley areas, commonly described as Mediterranean climates due to their moderate, wet winters and warm, dry summers, are in the process of planning their vegetables gardens for spring and summer.  Here are three common mistakes:

Choosing the wrong plants. Pictures in national gardening media can be enticing, but plants that require extended periods of moist soil and moderate, humid temperatures (tropical plants) are generally not a good choice for gardeners who live in California or other Mediterranean climates. So no matter how much you may want to grow your own ginger or turmeric or peanuts, most California gardeners are going to struggle with these plants and reap a limited harvest. Gardeners who want to make the extra effort may be successful growing some of these plants in  containers, where specific micro climates can be carefully controlled and modified.  See Ginger: Growing and Harvesting for Culinary Use and Turmeric: Container Gardening and Harvesting. Gardeners who live in Mediterranean climates can successfully grow many of the jewels of the home herb and vegetable garden, such as tomato, corn, lettuce, basil and pumpkin. Why not choose one or more of them?


Tomato ready for harvest.


Choosing the wrong varieties. Keep in mind that even for the same plant, there are typically many varieties with an array of characteristics. Gardeners who live in inland valleys will generally want to select heat-tolerant varieties that will last well into the summer; gardeners along the coast will typically want to grow “early” varieties that don’t require as much heat to fruit and ripen. And each area will have a slightly different palate of pests and diseases. For example, gardeners along the coast are typically more concerned with mildews and purchasing mildew resistant varieties can be critical to success. Seed catalogs and packaging labels in garden centers typically describe a particular variety’s resistance to specific diseases. For a complete guide see Common Terms for Seeds and What They Mean. 

Planting too early or too late. Plant too early and small plants may struggle in cool, wet weather. Plant too late, and plants may not have time to develop root systems necessary to pull enough water from the soil on hot summer days or develop leaf canopies large enough to protect ripening fruit from summer sun.

Planting too late can results in stress.

Planting too late can results in stress.


Gardeners in most of the United States plant spring seeds based on their USDA zone. However, USDA zones are inadequate for making informed decisions about what to grow in California because they are based on average annual minimum winter temperatures only, and do not take into consideration other critical factors for California gardening and landscaping, such as summer and winter high temperatures, annual rainfall, humidity, overall climate and seasonal changes in climate, or the number of days annually of hot weather or frost. The USDA zones place portions of Los Angeles in the same zone as San Francisco, despite the vastly different growing conditions, temperature ranges, climates, and high temperatures between those two cities. Much of California’s coastal inland and valley areas are frost free, so using minimum winter temperatures and USDA zones are generally not helpful. For this reason, GardenZeus uses a climate zone system optimized for California and for your individual zip code. To take complete advantage of GardenZeus resources for California gardening, go to GardenZeus, enter your zip code and select plants. For a complete explanation of GardenZeus climate zones, go to California Climate Zones.

And remember: heirloom and open-pollinated varieties typically have a longer time to maturity than many hybrids and need to be planted before many hybrids and “early” varieties of the same plant. Seeds catalogs usually list number of days to first harvest or maturity, sometimes listed as just a number (70 days), usually meaning the average number of days from the time the seed sprouts or the seedling emerges from the ground to the time fruit or flowers can be harvested. If you are planting in new or infertile soil, are new to gardening or inexperienced with the vegetable that you are planting, or working under challenging gardening conditions, the actual time to maturity may be longer than listed in seed descriptions, and in some cases much longer. To arrive at the total number of days from planting the seed to maturity, you need to add the germination time, which varies widely for different vegetables and flowers but is most commonly about a week or two. For more information, see How to Choose the Best Seeds for California Gardeners.

GardenZeus has comprehensive, customized growing information by plant and zip code. To get started, enter your zip code here.


New Year’s Resolution: Grow California Native and Mediterranean Plants

by Ann Clary and C. Darren Butler

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New Year’s Resolution 4: Grow California Native and Mediterranean Plants.

Will plants sold at local gardening centers and nurseries thrive in your garden or landscape? Often they will, but in some cases, climatically inappropriate plants are sold locally. For other plants, the unique conditions in your landscape might be problematic for a plant that will thrive at another location in your neighborhood or city.

This question is even more important when purchasing online or by mail. Many to most ornamentals, fruit trees, berries, and other perennials purchased from outside of California may fail to thrive, bloom, or produce a harvest in our Mediterranean-climate areas.

Native plants from California and other Mediterranean-climate areas can provide a solution. They are adapted to survive and thrive in the many unique climates and micro-climates in California. We often tend to associate California natives with a limited range of drought-tolerant species that are commonly used in home landscapes, many of which are suited to mild, wet winters and warm-to-hot dry summers. However, it’s important to remember that California has thousands of native plant species, including many natives that need frequent watering, high or low elevations, or other specific environmental or climate conditions. Considering California natives narrows your choices to plants that are known to thrive California, but you still need to confirm suitability of native or California-friendly plant species for the location and micro-climate where they will be planted.

California natives offer many advantages to the gardener. Here are a few:

1. Use less water. California and Mediterranean natives are often drought-tolerant, and may need little or no watering once established. Many native species have special adaptations or mechanisms that allow them to survive hot and dry summers, such as going dormant. How much would you save on your water bill if you eliminate all or almost all irrigation for landscape ornamentals?

2. Minimize the use of fertilizers and soil amendments. Many California natives thrive in the moderately alkaline, poor-to-moderately-fertile soils that are common in California. They may be harmed or killed in fertile, microbially active soils with high levels of organic matter that are needed for food gardening and growing many non-native ornamentals. Soils in California’s low-rainfall areas tend to be naturally low in organic matter and may never become loamy or highly fertile without human intervention. Imagine it! California native plants generally do well in the soils here, and they usually don’t need the endless bags of amendments, applications of compost, and other amendments and fertilizers.

Hummingbird Sage

Hummingbird Sage

3. Reduce pests and diseases. Reduce use of pesticides and chemicals. When grown appropriately and not overwatered or over-fertilized, California native plants often have fewer problems with pests and diseases than non-native ornamentals, and may be easily harmed by pesticides and other chemicals. Native plants and landscapes often tolerate or need few-to-no applications of pesticides and chemicals. 

4. Less maintenance. When native species are chosen carefully and are well-suited to their growing environments, many require minimal input from gardeners as compared with non-native ornamentals. Natives accommodate your busy lifestyle by not needing as much from you, and allow you to spend time relaxing or enjoying the beauty of your garden.

Why struggle with holly when you can grow Toyon easily?

Why struggle with holly when you can grow Toyon easily?

5. Ecosystem and biodiversity benefits. Native plants feed and provide habitat for native birds, animals, and insects, including pollinators. Some native shrub and tree species potentially provide benefits to dozens or hundreds of bird and insect species. Home gardeners can help maintain biodiversity in California and provide other ecosystem benefits by growing natives at home.


A bee on Ceanothus.

A bee on Ceanothus.

GardenZeus has customized gardening information by plant and zip code. To get started, enter your zip code here.


10 January Tasks for Mediterranean Gardeners

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Many might think of January as a slow month in the Mediterranean garden, as even in mild Mediterranean climates, January often brings cool, rainy weather. Yet there is much to do in January to prepare plants for their burst of growth when the weather warms in the spring. For a customized list of gardening tasks by plant and month, find your GardenZeus Climate Zone. 

Here are 10 tasks all gardeners in Mediterranean climates should have on their January to-do lists:

  • Monitor plants regularly, at least every 2 to 5 days during cool-to-cold weather to catch wilting, irrigation, pest, disease, weed, and other problems early.
  • Plant bare-root roses, fruit trees, vines and berries.
  • Prune roses and deciduous fruit trees.
  • Protect plants from possible frost: water thoroughly and protect plants with fabric, cardboard, paper, or plastic sheets during periods of overnight frost.
  • Maintain or add mulch to garden beds.
  • Harvest citrus trees and winter vegetable crops.
  • Irrigate variably depending upon rain frequency and volume; turn off irrigation during rainy periods.
  • Add appropriate amendments and/or organic fertilizers for actively growing and/or blooming plants. Avoid fertilizing dormant plants and trees.
  • Order seeds for spring annuals and spring and summer vegetables.
  • Start seeds indoors for later transplant outdoors, such as tomatoes, lettuce, and chard.

GardenZeus recommends seeds from Botanical Interests:

Other articles of interest:

New Year’s Resolution: Focus on Soil, Not Plants

New Year’s Resolution: Compost More Waste

New Year’s Resolution: Water Plants and Trees Deeply

Rain! Rain! Rain! But is it Enough to Water Plants?

GardenZeus has customized information by plant and zip code. To get started, click here.


New Year’s Resolution: Water Plants and Trees Deeply

New Year’s Gardening Resolution 3: Water Plants and Trees Deeply.

“How often and how much do plants and trees need to be watered?” is both one of the simplest and most-complex questions for gardeners.

The simple answer is that most plants should be watered to the entire depth of their roots, then not watered again until soil dries out to some degree, which varies by species.

The complex answer involves many factors and variables, including plant species, soil texture, and seasonal temperatures.

Sprinklers are useful for watering lawns and some small bedding plants, but are unsuited to watering almost all other plants and trees.

Reasons to avoid shallow, frequent irrigation:

– Plant roots grow where the water is. Shallow, frequent watering over time concentrates roots, even for large trees, in the top few inches of soil, where they may dry out rapidly and need frequent watering. Roots near the soil surface are most susceptible to pests, diseases, and injury.

– Spray irrigation or frequent wetting of stems and foliage encourages pests, diseases, and weeds.

– Shallow water results in greater evaporation with negative results, including faster accumulation of soil salts as minerals in municipal water are left behind in soil as water evaporates.

Slow, deep watering has many possible benefits including:

– Deeper, firmer rooting for trees and shrubs. Deeper roots increase a plant’s drought tolerance.

– Reduced evaporation and runoff.

– Reduction in pests, diseases, and weeds.

– Potential reduction in water use.

To water deeply, use a drip system or a trickle from a hose at a rate slow enough to prevent runoff. Many larger garden plants and landscape shrubs will benefit from slow watering for several minutes to an hour or two depending on plant size, soil texture, and watering rate/volume.

Drip irrigation used to water squash plant

Drip irrigation used to water squash plant

Learning to water your established trees and large shrubs takes time and observation. Irrigation volume and frequency vary by species and plant size. Observe shrubs and trees for early signs of drought stress, such as slight curling or drooping of leaves, then water deeply. If established trees need water again sooner than a few weeks, increase watering duration and/or volume.

In California Mediterranean-climate areas, many large shrubs and trees should be watered only once every few-to-several weeks during warm weather, and less often during cold weather, especially with occasional winter rainstorms. Trees should be watered at or just inside the dripline (the edge of the canopy).

Water penetration in soil can be evaluated by pressing a long screwdriver or thin metal probe into soil and noticing when soil resistance changes as dry soil is reached. This method can be used to gauge how fast water infiltrates to a foot or two in depth for a given method of irrigation. A shovel can also be pressed carefully into the soil outside or at the edge of an established plant’s root system to expose the soil profile and gauge depth of roots. For gardeners who want more precision and less guesswork, GardenZeus recommends a professional quality moisture meter inserted at the edge of the root system. (Picture below.)

Water spreads as it infiltrates into soil, narrowly in sandy soils and more widely in clay soils. If it takes your drip system or a trickle from your hose 1 hour to deliver water to a foot in depth in clay soil, it’s a reasonable guess that it should take about 6 to 8 hours of watering using the same method to deliver water to 4 to 5 feet in depth for a larger tree.

GardenZeus has customized gardening information by plant and zip code. To get started, click here.

Other articles of interest:

Rain! Rain! Rain! But is it Enough to Water Plants?

Chlorine, Soil, and Watering Gardens (Chlorinated Water, Part 1 of 2)

Remove Chlorine When Watering Organic Gardens (Chlorinated Water, Part 2 of 2)

New Year’s Resolution: Compost More Waste

New Year’s Gardening Resolution 2: Compost More Household and Garden Waste.

All life on Earth is made of the same building blocks, the organic elements. These include carbon, hydrogen, nitrogen, and many more that are recognizable to gardeners. Composting is the process of breaking down organic matter, which is any material that was once alive as part of a plant or animal, so that the basic building blocks can be reused for new life.

Composting occurs naturally in soil, at soil surfaces, and in nooks and crannies everywhere in gardens. Soil organic matter can be increased when cleaning up gardens by cutting expired plants at the soil line and leaving roots in soil to decompose. Quality compost is high in humus and humid acids, which contain the building blocks of plant life in ideal form for plant roots to absorb them.

Most of us can do better with being more thorough about composting. Enormous volumes of organic matter that could have composted are sent to landfills as household and yard waste. This has many polluting and negative environmental impacts, from the manufacturing and gasoline required to operate garbage trucks to otherwise reusable organic matter becoming toxified for the long term in landfills when it mixes with toxic chemicals and substances, toxic metals, commercial and manufacturing waste, and other toxic trash. Organic matter that has been cycling through life on Earth for millions of years may be tied up indefinitely in our human landfills once mixed with toxins.

Compost pile decomposing

Side view of compost pile in various stages of decomposition


Most gardeners know that they can compost apple cores, citrus peels, banana peels, and most food wastes but what about the following?:

– Eggshells: GardenZeus Expert Darren Butler considers eggshells to be the best source of calcium for soil and gardens. For many gardeners, they are too precious to put directly into a compost pile, and are used instead to provide extra calcium directly in soil or under mulch near tomatoes and other garden plants.

– Human hair and pet fur: Hair and fur contain nitrogen. They may break down slowly in compost.

– Pet bedding such as wood shavings from cages or aquariums

– Paper towels, napkins, and tissues

– Newsprint and newspapers: Most major newspapers in Southern California have been printed with non-metallic inks for years. Colored or glossy newsprint may contain pollutants. Check with your newsprint source.

– Paper and cardboard, especially with minimal printing or plant-based inks: Many online sources recommend composting printed paper, but toner and inks may contain plastics or other substances that are best kept out of soil. Use caution with recycled cardboard which may be best disposed of in the recycling bin, because it may contain bits of metal, plastic, or other pollutants.

– Plant wastes: All plant wastes are technically compostable. Some may take a long time to break down in a compost pile. In most cases it’s best not to compost plant materials that are diseased or pest-infested as doing so may perpetuate these problems in your soil and/or garden.

– Corn cobs and avocado pits, anyone?: These will compost . . . eventually. They may persist in compost bins for a year or longer.

– Dryer lint: Many online sources recommend composting dryer lint. GardenZeus expert Darren Butler agrees, provided that the lint is from natural-fiber clothes such as cotton or hemp. Dryer lint from synthetic fabrics may contain nylon, polyester, or plastic bits and threads that are best kept out of your garden soil.

– Cotton balls, paper/cotton Q-tips, and discarded cotton cloth: Be sure that these are cotton rather than synthetic.

– Sweepings and vacuumings: These contain mostly organic matter under normal household conditions. Recommended for composting when your home is nontoxic and you know that there aren’t pollutants on your floors or carpets. Most carpets are synthetic and stray pieces of carpet are best kept out of the compost pile.

–  Special care or expertise is needed to compost some organic household wastes safely, without unwanted smells, and without attracting rodents, such as meats, bird or animal bones, oils, and dairy. Domestic pet wastes may contain pathogens that cause disease in humans.

Composting is a gift to future generations, and helps to perpetuate life. It’s an age-old method for providing fertility to plants, and a necessity for sustainable living today.

Don’t have a compost bin?

GardenZeus recommends the following outdoor compost bin for your household and garden waste:

This container sits on your kitchen counter and holds your household waste before you place it in your outdoor compost bin. Odor free.

Want to read more about composting and the soil food web? Look no farther than the iconic gardening book, Teaming With Microbes.

Other articles about soil and composting:

New Year’s Resolution: Focus on Soil, Not Plants

Grow Cucurbits in Mature Compost Pile

GardenZeus has customized gardening information by plant and zip code. To get started, click here.

New Year’s Resolution: Focus on Soil, Not Plants

New Year’s Gardening Resolution 1: Focus on soil, not plants.

Everything that gardening experts, books, and if you’re lucky enough to have one, a gardening parent or grandparent, have told you that you need to do for plants, you actually need to do for soil.

Are you worried about watering your plants? Shift your worry to being sure that helpful soil bacteria, fungi, and other microbes are watered appropriately, even in areas where nothing is planted.

Do you feel you need a plan for feeding and fertilizing your plants? What you actually need is a plan for year-round feeding of the life in your soil, especially at times when you aren’t actively planting, there are no living roots in your soil, or your garden is dormant. In mild-winter California areas, soil life eats organic matter year-round.

Concerned about protecting your plants from insects, wind or harsh weather, or diseases? Protect the life in your soil first.

Soil that is vibrantly alive with a complex soil ecosystem provides ideal conditions to support healthy plants in a way that dirt, or the mostly-dead potting soil you buy in a bag at the nursery, never will. For a soil ecosystem to be healthy, it must be well-fed by plant-root exudates, which are sugars and other substances released by plant roots. Soil is also fed by dead cells from plant roots and root hairs; organic matter such as mulch at the soil surface; and the wastes and decaying bodies of both microorganisms (such as bacteria) and macroorganims (such as insects and worms).

When we shift focus to soil, our plants take care of themselves, or more accurately, soil life takes far better care of them than we ever could.

GardenZeus has customized gardening instructions by plant and zip code. To get started, click here.

Tips for Testing Soil pH at Home with A Soil pH Meter

Mud Pies and Fizz: Easy Home Tests for Soil pH

Gifts for Gardeners: Garden Clogs and Boots

GardenZeus receives commissions for purchases made through links in this post. There is no additional cost to you.

Have a gardener on your shopping list?

Keep your feet warm and dry this winter with the ideal garden clog. Wear them in the rain. Clean them with a hose.  Easy to slip on and off. Available in different styles and a wide variety of colors. Try the polka dots: reminiscent of Christmas lights! Available from Amazon.

Also available as a boot. Again, from Amazon.

The best thing you can do during rainstorms or when soils are wet may be to stay out of the garden! But after the rain, a careful check of your garden is in order, especially after heavy rains or storms that last for 2 to 3 days or longer. Be prepared to work in your wet garden with garden clogs, or give them as a gift!

For a complete discussion of rain in the California garden, see the GardenZeus series:

Part 1: Preparing for Rain in California Gardens

Part 2: California Gardening During Rainstorms: Flush Salts and Avoid Soil Compaction

Part 3: Benefits of Rain For California Gardens

Part 4: California Gardening After the Storm: What to do When the Sun Comes Out

Indoor and Potted Plants for the Holiday Season

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There’s nothing quite like live plants to bring up the holiday spirit and please a gardener’s heart. Some potted holiday plants and trees can survive indoors or when planted outdoors for months to years or even decades after the holidays, and they often don’t cost more than the price of 2 or 3 bouquets of cut flowers. Below are tips for favorites that are widely available during the holiday season.

Poinsettia (Euphorbia pulcherrima): Take special care with these fussy beauties. The most common reasons that poinsettias decline or lose their colorful bracts over the holidays are warm or cold temperatures, drafty conditions, insufficient light, and too much or too little water. They may decline at temperatures below 60 or above 70 degrees Fahrenheit, and may be damaged by several minutes of exposure to temperatures below 50°F. They need at least 6 hours of daily sunlight through a window or from an indoor fluorescent light, and prefer moist soil that isn’t wet or waterlogged. See Poinsettias: Tips, Care, and Fun Facts for the Holidays for compete information on growing poinsettias during the holidays.

Amaryllis (Hippeastrum cultivars): Hundreds of Amaryllis cultivars provide showy or even breathtaking single and double blooms in colors ranging from white to deep red, from salmon or peach to pink and maroon, and from solid single colors to striped and bicolored. Blooms may last weeks to months with proper care. Bulbs are welcome gifts for many gardeners who will grow them indoors after the holidays or even indoors/outdoors year-round. With proper care, some Hippeastrum species can survive and bloom for decades. Start early if you want to grow holiday Amaryllis from bulbs, in late September and October; many cultivars bloom 6 to 8 weeks after planting bulbs, but may take up to 12 weeks or longer. Be patient! Some Amarlyllis cultivars may take weeks to sprout leaves. During the holiday season, look for full-grown potted plants with healthy blooms or buds. Plant bulbs in pots with rich,well-drained potting soil and about 1/3 to 1/2 of the bulb above the soil surface. Water thoroughly, then allow soil to dry between waterings until bulbs sprout. Grow in a warm, sunny window after leaves emerge, and water more frequently during active growth and blooming so that soil stays slightly moist. Move plants to bright, indirect light when blooming begins.

Christmas Cactus (Schlumbergera species and hybrids): Despite the name, Christmas Cactus is a tropical epiphyte, meaning that it grows on trees or in nooks among rocks. Flower colors include white, pink, yellow, orange, red, and bicolors. Grow as an indoor plant in rich-but-well-drained soil, such as potting soil mixed with washed sand. Allow soil to dry slightly between waterings, and provide extra water while blooming. Plants bloom best when fertilized monthly from about March through October with a mild dilution of a balanced NPK fertilizer and a pinch or two of epsom salts in a separate feeding every 2 to 4 weeks. Christmas cactus needs plenty of bright light but avoid direct exposure to sunlight. Plants may be grown outdoors in bright shade during periods of mild daytime and nighttime temperatures.

Rosemary (Rosmarinus officinalis): Potted rosemary as trimmed to the shape of a mini Christmas tree can be a charming addition to holiday décor. Its lovely aroma is a welcome addition for many gardeners during the holidays. It grows well in potting soil mixed with washed sand, or in any moderately fertile soil that drains well. Allow soil to dry partially between waterings. Potted rosemary can thrive for years with occasional careful root pruning as needed in a medium or large pot, but may quickly overrun a smaller pot and suffer from being rootbound. Trim or pinch back frequently if you want to maintain compact, dense shape. Rosemary does not resprout from woody stems; take care to prune for stem structure and shape the plant while stems are still green. Rosemary does well planted outdoors in California Mediterranean areas with mild frost and winter temperatures down to about 25°F. It becomes very drought-tolerant once established in the ground. If kept in a pot, soak the entire pot in a bucket of water or run water through the pot for a few minutes every few months to flush soil salts that accumulate from evaporated water. Setting the pot outdoors during rainstorms will also flush salts.

Potted Christmas Trees: Various evergreen species are sold locally and by mail-order as potted Christmas trees during the holidays, including spruce, fir, cypress, and others. The vast majority of evergreen trees sold or shipped as potted Christmas trees won’t thrive and might not survive when planted outdoors in California Mediterranean areas. Norfolk Island Pine (Araucaria heterophylla) has an open form unlike the classic Christmas-tree shape of some spruce and fir species, but is often available as a potted holiday tree and survives well outdoors in Southern California coastal areas and mild-winter coastal-influence areas. If you want a live potted Christmas tree that you can plant outdoors after the holidays, try going to your local nursery and making a creative choice for an evergreen or other species suited to your climate, including those not necessarily sold as Christmas trees. You may find a species that can be trimmed into a Christmas-tree shape, or even if not, a tree that you can decorate now for the holidays, then enjoy in your outdoor landscape long after the holiday season has passed.

Other articles with holiday interest:

A Holiday Kiss Under the…Holly?: Mistletoe for The California Holidays, Part 1 of 3

A Holiday Kiss Under the…Tree-Killing Parasite?: Mistletoe for The California Holidays, Part 2 of 3

Super-Secret Trick to Evade a Kiss Under the Mistletoe: Mistletoe for the California Holidays, Part 3 of 3

Rain! Rain! Rain! But is it Enough to Water Plants?

During our ongoing drought in California, rainfall has become almost as exciting as a small earthquake. Failed rain forecasts seem ever more common, sometimes with less rain than predicted or no rain actually arriving. After so many disappointments, when I actually hear rain falling, I usually drop everything to rush outside in a state of semi-disbelief to witness the rain, just as I do when the first structural shaking from a little earthquake seems like it might be the start of a bigger earthquake.

For Californians who pay attention to the increased fire danger that results from statewide dry soils and low levels of moisture in plants and trees, and who are concerned about the numerous ecological and other impacts from drought, fall and winter rains are a hot topic. The first period of heavy rainfall is a cause for celebration; it provides decreased fire threat and many benefits to soils, trees, and plants, at least temporarily or until the next dry period.

Water-soluble soils salts accumulate from spring through fall in California’s Mediterranean-climate areas, or for a year or longer during droughts and in areas with low rainfall. Common sources of urban soil salts including fertilizers, minerals left behind from evaporated municipal irrigation water, and pet or wildlife urine. Salts tend to be concentrated in the first few inches to several inches of soil. Sufficient concentrations of salts cause stress to plants, are problematic for plant absorption of soil water, cause salt burn or brown dead leaf tips and margins, and if severe can kill plants and trees. Among many other reasons, sufficient annual rainfall is important for flushing salts deeper into soil where they won’t harm plants.

Small storms and brief or light fall-and-winter rainy periods might seem exciting, but they don’t provide much water to plants and soil. Irrigation calculations can be complex and technical depending on plant species, seasonal temperatures, and other factors. Most lawns and turfgrasses need about 1/3-inch or less water per week during cool-to-cold weather, and 1 to 2 inches of water per week during warm-to-hot weather.

Many of our brief fall-and-winter rainstorms in California Mediterranean-climate areas produce anywhere from about 1/20 of an inch of water to a third or half-an-inch of water. For comparison, sprinkler heads put out about 4/10-inch of water (for water-conserving sprinklers) to 1.5 inches or more per hour. This means that a light rainstorm over a few hours, or a heavy shorter rainy period that puts out 1/10 to 1/2 inch of water, is approximately the equivalent of running many lawn sprinklers for about 5 to 30 minutes, and it may provide sufficient water for lawns and small plants for a few days to a week or longer. This is a broad generalization. You can easily measure actual water output in your yard by setting out small uniform containers, measuring water output after running sprinklers for a specific number of minutes, and averaging results for an overall estimate.

An inch of rainfall that infiltrates completely into soil will normally travel to a depth of a few or more inches for clay and clay-loam soils to several inches or even a foot or more in sandy soils and coarse, rocky soils. In compacted clay soils, 1/10 inch of rainfall may sit at the soil surface and partially evaporate when the sun comes out, or infiltrate to a mere fraction of an inch. Clay soils often absorb only a portion or a fraction of an inch of rainfall per hour, while sandy soils may absorb 2 inches or more per hour.

What does this mean for water availability to plants and plant benefit from short California rainstorms? Depending on many factors from soil type to runoff, it means that rainstorms providing about 1/10 to 1/2 an inch of water provide short-term water for lawns, small plants, and bedding plants, with some benefit to shrubs and trees but not sufficient water to meet needs for trees and larger plants, to refresh water reserves in soil, to flush salts from upper soil, or even to meet water needs for lawns and small plants for more than a few days to a week.

During fall-and-winter periods in California with light and intermittent rainstorms, landscape plants may continue to need irrigation. Trees and large shrubs may still need deep watering every few weeks to few months. And unfortunately, fire danger, in both urban and wildland areas, may persist.

GardenZeus has customized growing information by plant and zip code. To get started, enter your zip code here.

Other articles of interest include:

California Gardening During Rainstorms: Flush Salts and Avoid Soil Compaction

Benefits of Rain for California Gardeners

Fire Armageddon is an Annual Event in California

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