Its hard to define sometimes but its essentially using the inherent characteristics of one plant to benefit other plants. Its building an ecosystem!
- Improve taste or effectiveness of a crop.
- Draw in beneficial insects.
- Fool plant predating insects.
- Trap Crop
- Shield Crop
- Physical advantages
- Nutrient advantages
The best companion plants may often times be a few weeds. Not enough weeds to choke out your young plants but enough to draw in naturally the beneficials you want.
Companion plants grown for this purpose are said to improve the taste of one of the companions. This – of course – is a highly debatable subject.
Plants high in volatile oils seem to improve taste of watery fruits and veggies. Tomatoes improved by basil. Cucumbers said to by dill. The general rule is that plants that go together on the plant go together in the garden.
Plants high in volatile oils improved by plants such as nettles. I can’t really discover why this is the case. Early mediterranean gardeners found that planting Basil (sweet) next to their tomato plants gave them larger, healthier, better tasting tomatoes. Perhaps the tomatoes’ roots absorb some root exudate of the basil, or “breathe” some secretion of this sweet smelling herb.
Draw in beneficial insects
Any plant that makes tons of flowers is going to help nearby plants. Flowers draw in among other things parasitic wasps and most plant predating insects go through a larval stage that is vulnerable to these wasps.
Yarrow, dill, lettuce (bolted), radishes, turnips, carrots, beets (in second year). All in all sunflowers are king. Buckwheat is good also.
You need a comprehensive flowering plan. Know what flowers when. Make sure you account not just for bloom times but also colors.
Large plants sunflowers but also corn. Corn has tons of nooks and crannies for lacewings.
Flowers mean bees. Especially orange and yellow flowers, draw them in. Calendula is great in this regard. Don’t just think about insects. Tubular flowers also draw in hummingbirds which can decimate a whitefly infestation.
Grapes take the cake as the best trap crop made. Aphids will go straight to grapes and they can’t really harm a strong grapevine but they will draw in tons of beneficials just by being there.
Eggplants seem to work pretty well as a trap crop for flea beetles, also groundcherries. Pick a plant in the same family of the one you want to protect, just make sure that plant is more appealing.
Things with strong smells or release things predating insects don’t care for.
Garlic – the aroma fools.
Nasturtiums – very peppery and strong.
Cilantro – stinks to me and to bugs.
Mint – easy to grow also.
Lemon basil and lemon balm – citronella
Provides support. Grew beans up grapes. Beans up corn.
Also includes co-planting and nurse crops. Co-planting is essentially planting two things so they grow at once (at some point). Like sowing clover and wheat.
Things like alfalfa mine the soil for nutrients. Bring those up. You can chop the plant and use it as mulch or let the fungi work their magic. Dandelions
There are bad companions too. Alliums next to legumes.
Fennel is said to be the worst companion.
Disease and pest proximity. Same family plants close by is a no-no. Tomatoes and potatoes- same blights.
Corn and tomatoes – rootworm. I noticed that parsley next to carrots is a no-no. The parsley drew in parsley worms (black swallowtail butterfly) and they also ate carrots.
Need to have a plan for companion planting. You garden layout should basically revolve around companion planting.