Know which plants make good bedfellows
It was getting to be late summer one year, and the cucumber vines had reached the top of the strings on which they were growing. We had even looped them over the metal bar from which the strings were suspended, and they had begun their descent downward. At the bottom of the vines, we removed any leaves that had, for whatever reason, lost the bloom of health.
The plants were growing in 30-inch-wide beds, with one row down the center of each bed. This left plenty of room on either side, and because it was time to get serious about fall crops, we decided to plant rows of lettuce in those spaces. Lettuce germinates best when the soil temperature is in the low 70s and declines as you approach 80, so it's best not to jump the gun on sowing. We figured that the cucumber plants would shade the lettuce a bit on warm days and that there still would be enough light for growth. When the weather cooled and it was time to take the cuke vines down, the lettuce would have the bed all to itself.
Our plan worked fine that year, and it was typical of the kind of space-saving maneuvers we take advantage of whenever we can. For example, we once planted some small pepper plants fairly widely apart, knowing they eventually would grow large and bushy. But by broadcasting arugula seeds around them, we were able to feast on this cut-and-come-again green in the cool spring weather it so enjoys before it yielded the ground to the peppers.
In the spring, we might also interplant early crops with a single row of Brussels sprouts, and they, too, would need the whole bed. In the meantime, there's plenty of room to sow baby spring carrots, baby beets, salad greens or radishes on both edges.
Could we have sown another crop under the trellised tomatoes as well? We sometimes put basil there because both plants do fine in hot weather, and a little shade for the basil might slow its tendency to bolt. Because they also taste good together, we pick them at the same time. But tomatoes do drop their fruits on the soil, and not everything would put up with that.
Pole beans, on the other hand, would be extra kind to an understory crop, thanks to the nitrogen-fixing nodules that form on their roots. We'd strip off some of the lower leaves and then plant fall brassicas, such as Japanese baby turnips or zesty red mustard, because brassicas always appreciate nitrogen-rich soil. In the classic "three sisters" gardens planted by certain American Indian tribes, beans provide nitrogen for companionable squash and corn.
Another trick of plant cohabitation is to mix crops that occupy different strata of the soil. Shallow-rooted members of the allium tribe, such as onions, leeks and scallions, go well with the deep taproots of lettuce and carrots.
These are all good schemes for the cozy little world of the vegetable garden, but it's eye-opening to see how they can be practiced on a larger stage. Fruit growers will plant bands of diverse, nectar-rich flowers between rows of trees. Not only do they attract pollinating insects, but many insects lured by summer flowers will feast on the larvae of fruit pests as well.
In the wild, plants find their niches as best as they can. The landscape may shift in time, not only in the course of a year, but also more slowly, as pioneering species are pre-empted, in stages, by increasingly long-lived ones. In the seasonal garden, it's the same - but you choose the bedfellows.