A long-known strategy to maximize the growth of your vegetable garden is called companion planting. Revived in the 1970s as interest in organic gardening methods grew, companion planting uses the protective, attractive and chemically compatible qualities of vegetable plants to foster mutually healthy growth. In "Carrots Love Tomatoes," Louise Riotte popularized traditional planting knowledge and modern growing information to introduce new generations of gardeners to companion planting. Use old and new ways together to increase your collards crop.
Collards as a Family Member
Collards are a member of the Brassicaceae family, along with cabbage, broccoli, kale and cauliflower. Knowing this can helps you organize compatible plantings in your garden. If hyssop, thyme, and artemesia repel the white cabbage butterfly from cabbage, they will also repel it from collard leaves. Some charts of companion plants are organized by families and a gardener's own experience; if companions for the plant you seek are few or nonexistent, look at listings for family members. Avoid planting lots of family members close together; they will all deplete a similar set of nutrients and do less well than they might with other neighbors.
Attractors and Repellers
Aromatic herbs have beneficial effects on collards and other Brassicacaea family members: hyssop, thyme and artemesia are listed as cabbage-moth repellers. Another facet of companionship is attraction: sage, mint and dill are recommended. While little is said about the properties of sage and mint, they tend to draw some insects but not all. The role of dill is more complex; it draws a kind of wasp that attacks cabbage worms.
Plants with Different Needs
One important companion technique involves grouping plants that use different strata or chemicals from the same soil. Potatoes and onions are suggested because their nutritional needs are different from collards and because they draw nutrition from different areas of the soil. This prevents the kind of soil depletion and need for extra fertilizer that would occur if collards, cabbages and brussels sprouts were planted together.
When pest infestation is particularly hard to control, one companion strategy is to plant a trap crop to salvage a crop of greater value. In plantings of six sample crops all vulnerable to harlequin bug, mustard greens became the trap crop. Bugs ate large amounts of easily sown, quick-crop mustard, leaving crops of arugula, collard, beans, rape and rapini only slightly damaged (the too-full-for-dessert strategy). Research continues on the benefits of trap crops for a wide variety of pests and produce.
When Gardeners Disagree
One companion planting guide enthusiastically endorses the interplanting of tomatoes and collards. Another ignores collards, stating flatly that cabbages hate tomatoes. If possible, make room for a small field test. Pairs of plants are not enough to draw scientific conclusions, but you may enjoy some surprising successes. Many factors--soil content, water, plant variety, weather--affect the ultimate success of plants, and you may be the next gardener to contribute both wisdom to the literature and dinner to the table in organic garden growing.