Who’s your neighbor?
In Sand County Almanac, Aldo Leopold stated regarding the affinity between pine trees and dewberries, “When I plant a white pine in a dewberry patch… he will outgrow and outbloom his fellows planted on the same day, with the same care, in the same soil, but in the company of grass.”
Since it is time for gardeners to plant things, now’s the time to report anecdotes and occasional scientific verifications regarding the phenomenon that some plants grow well together and some don’t. Plants might benefit neighbors by being aromatic or stinky, by exchanging chemicals and nutrients underground, or by spreading out big floppy leaves to discourage unwanted invasives.
Plant symbiosis is a name for the ability of plants to benefit each other in one way or another. However, certain juxtapositions are deleterious, and it is important to know the difference. Much of the companion planting data is anecdotal, and only recently have there been scientific studies, but we shall proceed undeterred in passing along advice of all kinds.
Asparagus seems to like having a few parsley plants mixed in. Parsley is a biennial, however, and develops in its second year into a tall, bushy specimen with a long taproot which might interfere with nearby asparagus crowns. Maybe harvest parsley at the end of the first season.
Parsley also is a happy companion for tomato plants because it attracts hoverflies that eat roving gangs of aphids and feed on hornworm eggs which is a good thing.
Tomato plants also benefit from the presence of marigolds and basil, which repel whiteflies. Marigold roots exude an underground chemical which hinders the growth of certain nematodes. According to folks who look through microscopes at soil, some nematodes prey on tiny garden pests, another good thing, but others are pests that attack your favorite garden plants. Marigolds (to the rescue) deter the gangster nematodes.
Basil pairs well with tomatoes in recipes and also in gardens. Gardeners through history claim the aroma of basil repels white flies and hornworms but its nearby presence seems to boost tomato production. Try it and see, and add an assortment of marigolds for color and magical protection.
Also regarding tomatoes, and this is important, a European observer claimed tomatoes protected gooseberries from insect pests. Maybe you already knew that. I had no idea.
Radishes are a good companion for peas, and beside cucumber plants they keep cucumber beetles away. Supposedly lettuce nearby makes radishes tender but chervil makes radishes hotter. I grew chervil once. Do you ever wonder who first noticed these things, and was it years-long study done by graduate students to analyze the effect of chervil on radishes? Just like speed limits, these are suggestions.
Lettuce and beets get along. They play cards with snow peas on Tuesday nights. In fact, behind snow peas on a trellis there’s a shady area for one more lettuce crop late spring before the weather gets too warm and peas fade. Plant beets and radishes on the front side, and everything will be finished just in time to plant your second cucumber crop on the trellis.
Experiments in mid-20th century demonstrated that bush beans produced better when planted in strawberry beds compared to bush beans left by themselves with no one to talk to. Strawberries also experienced a boost, so there is something else to try. Strawberries also like borage, and so do I. As a side note, pine straw is the recommended mulch for strawberries.
Allelopathy is the name for plant companionships, just so you know, and an example is while a carrot is shooting downward, it exudes a chemical which has a positive effect on nearby peas.
And if carrot flies are your nightmare, plant salsify and it will scare them away. Now you know where to plant your salsify.
To put this in perspective, one renowned source claimed, “When charlock seeds are present in the soil, they are awakened by the presence of oat seed.” But, take heed – beets are harmed by charlock! You have been warned.