Onions provide mild pest discouragement that may help many other vegetables, especially when other vegetables are planted sparsely among denser plantings of onions.
Onions are antagonists to beans and peas; traditionally these plants are believed to stunt or negatively affect each others’ growth. GardenZeus expert Darren Butler has seemingly endless bits of gardening lore and anecdotes of unknown origin that knock around and occasionally shake loose inside his head. One such orphaned gardening thought is that some onion exudates, which are substances excreted by plant roots, can be absorbed by pea and bean plants and may result in sour or bitter, oniony-tasting legumes. If this is actually true, with foodie interest in novelty and gourmet vegetables, one might expect onion-flavored peas to headline many a pricey menu, with peas and beans grown inside an onion jungle to have their 15 minutes of fame as the newest trendy cash crop. In any case, traditional consensus suggests that planting onions near peas and beans is unwise to the point of bordering on the perilous.
GardenZeus expert Darren Butler has succeeded well with planting onions and other alliums among strawberries, although pest discouragement for slugs and snails on strawberry fruits is less than some enthusiastic gardening books or websites might suggest (the slugs and snails have all morning or all evening with nothing better to do than find a pathway through your maze of onions to the ripe strawberries that you were just about to pick). Other recommended and traditional companions for onions are lettuce, tomatoes, and herbs such dill, parsley, or mint. Chamomile and summer savory as companion plants purportedly improve the flavor of onions.
Many sources recommend planting onions with other root crops such as beets, carrots, and potatoes, and while these plants may provide benefits to each other, there may also be disturbance to the roots of whatever crops are left in the ground when others are harvested. Carrots are sensitive, especially when young, and harvest of nearby onion roots may cause splitting or forking in carrot roots. GardenZeus recommends caution and extra spacing when planting root crops as companions.
Onions are useful in crop rotation as they repel many of the pests that thrive on other vegetables. If you’re having pest problems with any vegetable except another allium, especially with tomatoes, potatoes, and carrots, try rotating onions into the problem area every other year.
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