September: A Breathing Space

During our heat waves this year, the nighttime has felt like a refuge of coolness and peace after the daily onslaught of heat.

Most plants feel the same way. During the day, they use sunlight and water to make sugars by photosynthesis. During their nighttime rest, they are able to use those sugars to make new cells. If it sometimes seems to you that your plants get larger overnight, you’re right-- they do.

September’s combination of warm soil, sunshine, and longer nights gives seedlings perfect conditions for fast growth, as long as they have access to water. Starting seedlings in trays is one way to give them the conditions they need when the open garden is still too hot, too dry, too windy, too crowded, or too weedy for good seed germination. Or start seeds in the garden and water them often. But start them now, before frosty nights and shorter days slow down or stop growth.

In the last decade, research on plants and soils has created a quiet revolution in how we understand growth and fertility. Most gardeners have not heard about it yet, but it turns out that fertile soils get that way not primarily from minerals or from additions like manure, but from plants themselves.

Plants use the energy of the sun to make sugars and other carbon-based nutrients. Some of those carbs become part of the plant’s tissues–that’s the story we always knew. But up to 2/3 of these sugars and other compounds ooze from the plant roots into the soil. The carbs in these root exudates, as well as the carbon from decaying plant roots in the ground, are the fuel that feeds soil life–fungi, bacteria, and zillions more. These soil microorganisms make nitrogen for plants to eat. They also convert minerals in the soil to a form plants can absorb.

The reason that forests grow so lush without fertilizer or amendments is that the soil is full of undisturbed roots–living and dead. The surface has a constant mulch of dead leaves and other organic matter. No plow or tiller disrupts the web of underground life.

Where to start on a garden scale? Leave plant roots (except perennial weeds) in the ground rather than pulling them out. Use mulch. And plant cover crops this month. Don’t wait for your summer crops to be over–scratch in some seed around your tomatoes and squash, then mulch over it. If you want something that will overwinter, feed the soil, and be easy to cut down next spring, try vetch, crimson clover, bell beans, or Austrian Winter peas.

With winter peas and fava beans, you can have both a food crop and a cover crop in zones 7-10. Don’t wait for pods–just clip the shoots for salads and light cooking. They taste like peas, and are ready in less than a month. You can even grow them on a window sill. Get them started now, and you will have fresh new flavors when the tomatoes and zucchini are just a memory.

Another thing to consider this month is how to use any space you have under cover. A greenhouse, cold frame, or tunnel doesn’t just keep the plants warmer, it also keeps them from getting beat up by wind, muddy, and slug-gnawed. Peas, broccoli, and lettuce respond particularly well to protection; they are fairly fragile plants that like cool conditions but can’t take a lot of punishment from wind and wet.

Easy crops that tolerate some cold and wet are turnips, miner’s lettuce, erba stella, nappa cabbage, tatsoi, mustard, mizuna, fava beans, endive, and cilantro. All of these do well for me outdoors. Depending on how cold your winters get, they may need protection, but they are not fussy and are very fast-growing. Miner's Lettuce, Erba Stella, Mizuna, Tatsoi, and Yukina are all hardy enough to grow in tunnels in New England. Even a few plants can make fresh salad material if you harvest the outer leaves every week or so.