How To Use Trap Plants For Companion Planting

One of the interesting things in the vegetable garden is the existence of “trap plants” we can use to both attract and identify pest infestations as a form of companion planting.

For example, beans and eggplant are beloved of spider mite and white flies so if you want to know if these pests are a problem in your garden, check these two plants first.

Or, if you’ve had a problem with these pests in the past, do plant these plants so they’ll both attract the pests (taking them away from other plants such as tomatoes) and give you an easy  place to spray insecticidal soap for control purposes.

This means you can actually put some eggplant and bean plants next to other plants that have had insect problems in the past to use as “traps” and infestation early warning signals.  A few plants scattered here and there through the garden works really well instead of concentrating these two plants in a section all by themselves.

The first is that it works and has a great deal of scientific study behind it.
The second thing is that it’s easy to do. I know few gardeners who really understand the full anecdotal companion-planting systems other than a few basic interactions.

Trap-cropping is a simple system with limited plants to use.
The plants listed below attract the indicated pests. Period.
This means the insects prefer to eat the trap crop (most do anyway) instead of your preferred plant. This gives two positive results – the first is that your preferred plant isn’t being eaten and the second is that the majority of pests are all in one place, making it much easier to kill them. Because this is what you’re going to do – kill the pests attacking the trap crop.
Differences To Note

I note much of the research has been done on commercial farms where the trap crop is a row or two on the outside or running between rows of the desired crop. It is on a much larger scale than backyard gardens so there are a few more details to be aware of and techniques to be used along with trap-cropping.
Diverse planting – this means plant a lot of different kinds of plants – vegetables, herbs and annual flowers in the same area. Insects are less likely to build up into total crop-devouring numbers when there aren’t large mono-cultures. (All the same kind of plant.)
Did I mention to include flowers in the vegetable garden? These will attract a great many beneficial insects as well as provide some beauty in your garden. And a cutting garden of your favorite flowers will fit right into a vegetable garden as both flowers and vegetables are constantly being cut and pruned
My advice about which flower to plant would include marigolds, geraniums, asters and zinnias as the base plants (all have been shown to attract insects), but also include your favorite flowers for cutting. Don’t be restricted by what’s “good” for the garden but instead consider what’s good for the gardener.

Commercially Used Combinations You Can Use in the Home Garden

These suggestions are gleaned from commercial vegetable production research and studies and are recommended for big growers. I suggest home gardeners can take advantage of these as well.
Again, a trap crop will attract the pest first but it won’t “protect” the main crop in any way.
You do have to control the insect but at least you know where it’s more likely to be first. Check these trap crops regularly for the beginning stages of insect infestation. When you see them on the trap crop, control immediately before the insect moves to your preferred crop.
Chevil attracts slugs. Plant with everything as it’s a favorite slug food.
Chinese cabbage seems to attract more Cabbage webworms, flea hoppers and mustard aphids than regular cabbage. Plant this form next to your regular cabbage.
Dill and Lovage are preferred foods of the tomato hornworm so mix these herbs into your tomato plantings.
Hot cherry peppers are used as trap crops for regular sweet bell peppers to attract pepper maggots. Plant all peppers in the same area but check those hot cherry types first for problems.
Peppers also attract aphids probably more than any other vegetable – check this crop first and plant it next to any other plant you want to protect.
Marigolds deter root-knot nematodes so plant next to legumes (peas, beans) that are a main food crop of this pest.
Nasturtiums are beloved and eaten by aphids, flea beetles, cucumber beetles and squash vine borers. Plant them either next to or among your cabbage and squash plant families.
Radishes are eaten by flea beetles and root maggots more than cabbage so plant radishes between your cabbages.

Tansy is a great food source for Colorado potato beetles so plant it next to your potato crop.