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  • Writer's pictureStacey Evers

Fall garden advice from an expert

It's the veggie gardener's autumn dilemma: Keep the tomatoes for a little bit longer or remove them?

Remove them, says US Botanic Garden vegetable gardener Thomas Crawley.

"I let the fall crops drive the schedule," Crawley said during an online Q&A hosted by USBG on Oct. 1. "In the next few weeks, the tomatoes will be done anyway. Give the extra week to the fall crops."

At the USBG kitchen garden in Bartholdi Park, the team of gardeners has transitioned the plots entirely to cool-season crops, including three kinds of beets, kale and kalettes, chard, spinach, garlic and oats. They were started in the greenhouse nearly two months prior to planting. Although it's hard to believe, especially given the warm, humid weather this week, the USBG gardeners are "on watch for the first frost in the next two weeks and we don't want tender plants."

While it's too late to direct-sow most plants now, Crawley said you can still get in radish seeds. (Radishes can be harvested as soon as 3 weeks after their seeds are sown.) You can also plant winter lettuces, garlic and onion sets, and hardy greens like kale, arugula and chard. These greens are cut-and-come again, so you just pull the outer leaves while the rest of the plant remains in the ground. "A couple of 20-degree nights won't kill them," he said.

Choose plants that are at least six weeks old or have four true leaves. Cabbage in 6" pots can still be transplanted as well. While the window of opportunity for the fall garden is likely to close soon, Crawley noted, "I've gambled and won several times in this region."

Garlic planted now should be ready for harvest by June. Crawley recommended thinking of your garlic and onion sets like tulips: they're all bulbs and can be planted into late fall.

Cover crops, the answer to every lazy gardener's prayer, can also be planted in October. During the winter while we're inside poring over seed catalogs and watching DIY garden videos on YouTube, cover crops outside are replenishing the soil's nutrients, blocking weeds, aerating the soil, preventing erosion and reducing runoff.

An oilseed radish is a soilbuster!

Many cover crops are grasses: oats, barley, winter wheat. Others, like clover, hairy vetch and winter peas, put nitrogen in the soil. Deep-till radishes, like daikon (of which oilseed is a type), break up clumped or compressed soil. (Check out this quick explainer to learn more about cover crops.) Crawley plants cover crops in plots on a rotation. He aims to not repeat plant families in the same spot for at least four years, and the cover crops serve as a placeholder between edible crops.

Consider extending the growing season with cold frames, low tunnels or small greenhouses. If the frames are sturdy enough, your greens may grow all winter. The USBG kitchen garden has two types of cold frames, pictured below. A slanted frame's cover should have a pitch between 35 and 60 degrees, and the box should face southeast.

By using these devices, Crawley said, vegetable gardeners can

  • Grow further into fall and maybe all winter. Make sure that any cold frame has removeable or hinged lids; Crawley's frame once reached 120F in January.

  • Start growing earlier in the spring, perhaps as soon as late February

Eventually, though, the shortened days might get the best of your winter garden. "Even if you can keep them warm, light is a factor," Crawley said.

Do you have a garden question? Contact the US Botanic Garden's hotline by calling 202-226-4785 or filling out the online form.

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