Practical Tips for Summer-Sown Seedlings

16 July 2020, written by Barbara Pleasant

It’s looking like the stay-home lifestyle will be with us for a while, which is an excellent reason to gear up for a great autumn garden. Why look at vacant space or overgrown weeds when you could be growing Chinese cabbage or broccolini? Some vegetables like rocket and daikon radishes grow best after midsummer, and autumn is the best season for growing tender collards and spectacular spinach.

Of course, there is a catch. As days become shorter sunlight intensity also decreases, resulting in a steady reduction in solar energy, which green plants depend on. This is why vegetables grown in late summer and autumn mature about three weeks later than they might when grown in spring, and why your autumn garden must be planned and planted now. If you wait until you can sense autumn in the air, you’ve waited too long.

Starting Your Autumn Garden Seedlings

The autumn garden gives you a new chance to work with seeds, which is always fun. Mail-order seed suppliers have replenished their stock since spring, so it’s easier to find interesting varieties now than it was back in March. I usually find plenty of seeds to work with in my seed box, and I try to use up opened lettuce and carrot seed packets, and other seeds with a short storage life.

Just like in spring, I start cabbage, kohlrabi, lettuce, and many other seeds indoors, where they sprout quickly at warm room temperature. I often keep new sprouts under my fluorescent grow light for a day or two, and then move them to a shady spot outdoors so they can start taking in real sunlight.

“Protecting — Cover seeded beds with cloth or horticultural fleece to keep them moist

Look around for a convenient outdoor spot for growing seedlings in summer. My setup consists of a glass-topped patio table with umbrella, placed in a sunny part of my deck. The umbrella’s shade pattern changes during the day as the sun moves across the sky, so the seedlings get a little sun but mostly bright shade. When stormy weather is predicted, I take down the umbrella and put the little plants under the table where they are protected from hammering rain. Even without the umbrella, the space under a glass patio table makes a nice niche for chard, Chinese cabbage, or other seedlings for the fall garden.

Using Shade Covers to Protect Direct-Seeded Autumn Vegetables

Many excellent autumn-cropping vegetables resent transplanting and must be started from direct-sown seeds, including carrots, turnips and all types of radishes. Carrots and Asian daikon and watermelon radishes need as much growing time as they can get, which means planting the seeds in hot weather. Plant seeds just before a period of rainy weather is expected if you can. Otherwise, use shade covers to keep seeded beds cool and moist.

In hot areas in midsummer, I suggest using a double cover consisting of a lightweight cloth placed over the ground, with a second shade cover suspended over hoops. Old sheets make good shade covers, or you can use horticultural fleece. With a double cover in place, you will need to water only once a day in dry weather to keep the seedbed moist. Remove the ground cover cloth as soon as the seeds germinate, but keep the hoop cover in place to protect the seedlings from pests, predators and violent storms.

Preventing Autumn Garden Pests

The best type of plant cover for the late summer season is tulle, also called wedding net. The holes are small enough to exclude most pests, but the weave is so loose that tulle covers do not retain heat. From transplanting day onward I use tulle cover to keep cabbage white butterflies away from cabbage family crops, and to exclude rabbits from the autumn carrot patch.

You also can use regular horticultural fleece, which does retain heat, but the heat buildup is offset by the 15-30% reduction in light transmission from the cover. As a result, broccoli and cabbage seedlings set out under row cover in late summer may surprise you with their vigour, despite hot weather. Just be sure they get plenty of water.

Especially if you are a new gardener, I hope you will give autumn gardening a try. Be willing to try different things that grow especially well in autumn, for example rocket, turnips or baby pak choi. Start some seeds now, and look forward to a great ending to your gardening season.