I walked out into the garden the other day with beet and kohlrabi seed packets in my hand. Both vegetables are popular in our home. But where to sow them? Some space at the end of a bed given over largely to onions seemed suitable.
First, I checked in a little book. Yes, it said, all three vegetables get along well with one another. So I went ahead and sowed the seed.
When the late Ruth Stout was once asked what she thought about companion planting, she replied that she believed it to be a valid concept but that she never bothered with it in her garden.
"All my plants get on well with each other," she added.
One of the more famous practitioners of all-mulch, no-dig gardening, Ruth had soil so rich in humus and plant nutrients that she invariably enjoyed good harvests no matter what vegetable was planted next to what.
That is the philosophy of many gardeners. But enough study has been done in recent years to suggest that good harvests may become even better harvests if companion planting is practiced. Moreover, much of the research has been collated in readily available printed form so that such a program of planting is simple to undertake.
Companion planting takes advantage of the fact that vegetables, like people, often enjoy the company of others outside the immediate family circle. It is siting together those friendly vegetables that help one another when they are grown side by side and keeping separate those vegetables that find each other's company less than agreeable.
Companion planting is often advisable because of plants' natural chemical tools for communication -- secretions put out by roots and volatile oils evaporating as scent from leaves and flowers.
Vegetables display their friendship either by growth stimulation (the way basil when planted near tomatoes seems to stimulate tomato growth and flavor) or by warding off pests (the way leeks planted near carrots drive away the carrot fly).
Carrots return the favor by confusing the onion fly, whose progeny eat all members of the onion family.
Even more important is to avoid planting close together those vegetables that are repellent to each other.
I once learned that to my cost. In the days when I knew no better, I planted a row of tomatoes side by side with a row of potatoes. They happen to belong to the same family -- first cousins, you might say -- so why not? Indeed, they grew well enough on the surface. The tomatoes yielded well, but when I dug up the otherwise thriving potatoes, only a few undersize tubers turned up. What should have put potatoes on the dinner plate for weeks on end provided enough, as I recall, for about two family meals.
I have since discovered why this was. Tomatoes, being from the same family, enjoy roughly similar conditions and nutrients. Potatoes, with spreading underground tubers, would soon take over the turf if left unchecked. So to defend its territory, the tomato exudes a growth inhibitor from its roots. This doesn't seem to affect the top growth of the potato quite so much, but it markedly cuts down on tuber production -- and it's tubers the gardener wants, not good-looking leaves.
By some estimates companion planting can come close to doubling a garden's total yield. Thus, where can we get the necessary information?
I'm now using the book Carrots Love Tomatoes ($5.95, Garden Way Publishing, Burlington, Vt. 05445) by long-time garden writer Louise Riotte. It is a detailed, A-to-Z compilation that is informative -- and even entertaining at times. It deals with what to grow with what plant and, equally important, what notm to grow together.
On a smaller scale, the May-June issue (No. 69) of The Mother Earth News has a center-page spread dealing with the companion likes and dislikes of 44 common garden vegetables. Or, for $2.50, you can obtain a 17-by-22-inch expanded version of what appears on that center page by writing to: Focusing, PO Box 472, Oroville, Wash. 98844.
It is probably wise to remember that companion planting is hardly an exact science. While some knowledge stems from replicated experiments by university scientists, much of the advice is the result of observations made by good gardeners down the centuries.
As a result, the effects of companion planting are often better docum ented than the causes.