Time to Plant Cool-Season Crops

August 18, 2013

 August might not seem like the perfect time to be sowing seed, but for some plants the timing is perfect. Just this week, I sowed seed for some of my favorite fall vegetable crops as well as for a few spring blooming biannual flowers.

Cool season crops like kale, broccoli, cauliflower and carrots can all be sown now so they will have a jump-start when cooler temperatures arrive.

In my area of Rhode Island, mid- to late August is when a noticeable difference occurs between daytime and nighttime temperatures. Warm days followed by cool nights are perfect for starting seedlings of cool season crops. Care must be taken, however, not to cook tender seedlings in the hot summer sun.

I sow seeds just as I do in the spring, in flats of seed starter mix. After sowing, I place the flats in a shady spot and am careful to avoid letting them dry out while the seed is germinating.

Once the seed has germinated, I move the flats to brighter light situations. To avoid overheating the seedlings, I place the flats in a location that receives direct morning sunlight from dawn until about noon.

Hot midday sun from noon until about 3:30 can be tough on seedlings that prefer cool temperatures. Keeping them in dappled light during those hours allows them to receive enough sun to stay healthy and prevents them from drying out or suffering from too much heat.

Once my seedlings have their second set of leaves, I transplant them either into individual cell packs or into fiber packs of four plants per box, where they have room to mature a bit before being planted out in the garden.

Usually, toward the end of August, average temperatures are beginning to moderate in my area. This is the perfect time to transplant directly into the garden.

I try to transplant on cloudy days if I can, and I always transplant in the morning when temperatures are cooler to avoid stressing the young plants. I also water the plants in well, including the soil surrounding the transplants. I have found that keeping the soil evenly moist in an area about 12 to 18 inches around the newly transplanted plants helps them send their roots out faster than if just the plants themselves are kept watered.

After three or four days, I water the transplants with a solution of fish emulsion and repeat every 10 days until the plants are large and healthy. After that, the plants are on their own. I add large amounts of compost to my garden every spring, which keeps the organic content of the soil high. I have found that with healthy, well-amended soil, supplemental fertilizer is not necessary. I do add an organic granular fertilizer prior to planting every spring and plant a cover crop of winter rye every fall.

As is the case with spring planted brassicas such as broccoli, kale and cauliflower, the voracious larvae from cabbage butterflies can be a real problem.

Cabbage butterflies are fairly common across much of North America. These small, white to sulfur-yellow butterflies with black spots on their wings lay eggs on the leaves of almost all members of the brassica family.

Once the eggs hatch the tiny green caterpillars that emerge eat small holes in their host’s leaves. The caterpillars grow rapidly, and soon the small holes become larger holes. A bad infestation can completely defoliate a plant in a very short time.

Covering young plants with remay, a thin, lightweight fabric that allows water and light to pass through, prevents the butterflies from laying their eggs on the plants leaves.

Another safe method of control for plants already infested is to spray with Bacillus thuringiensis, often called Bt. Bt is a naturally occurring bacterium that contains a protein that, when ingested by caterpillars, is lethal. Bt is available in most garden centers.

I plant cool-season crops into the spaces in my garden left empty from harvested crops.

In addition to transplants, I also direct sow seed for crops like spinach, lettuce and radishes. I wait to sow these fast growing vegetables until I am sure the heat of summer is past.

If your garden is ready to quit for the season, before you are, planting a variety of cool season vegetables will keep it up and running until frost, and even a bit longer.

This post was originally published in the Chicago Tribune on August 9, 2013.


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