mustard
August is the time for harvesting the summer’s bounty in the vegetable garden. But it is also the time to sow seeds for cool season veggies that thrive in the fall and winter. Even though it is hot and humid, by sowing now, your veggies will have the time to achieve maturity before day length gets too short. Also, it takes just a little longer to achieve maturity in the fall. But the good news is that often these plants are not bothered by as much disease and pests as in the summer.
Cool season crops include carrots, green onions (scallions), cauliflower, broccoli, broccoli raab, Brussels sprouts, cabbage, collards, spinach, Swiss chard, radish, turnip, and Asian or hardy greens such as mustard, tatsoi, mache, and kale. You still have time to plant garlic: that’s in October.
tatsoi
You can either purchase transplants from local garden centers or sow seed. To determine when to sow seed, look at the “days to maturity” on the seed packet. Count backwards from the average first frost date to determine when to plant. I use Halloween as my marker for a frost in Northern Virginia. When you are sowing seeds in the fall you have to take into account that day length is getting shorter. This “Short Day” factor is not addressed on the seed packet. If you are going to sow seed instead of purchasing a transplant from the garden center, you have to add 2 weeks to the numbers on the seed packet to allow for the cooler night temperatures and the shorter day lengths. For example, to sow spinach seeds add 7 to 10 days for germination, 35 days to reach maturation, and 14 days for the Short Day factor for a total of 56 to 59 days.
One of the reasons why you start your seeds in August for a fall/winter garden is the Persephone period, where daylight starts to be less than 10 hours per day. When daylight is less than 10 hours, the plant stops growth. It is still alive, just “dormant” until daylight begins to increase a month later. This is based on latitude. Enter your zip code in the almanac website. Where I live, I entered November dates randomly in the almanac until I found a date close to 10 hours. I decided to use November 15, 2024, as the marker: it will be 10 hours and 5 minutes. I can then calculate that from August 1, I have 15 weeks to start a plant from seed to maturity. From September 1, it is 11 weeks. It is important to start the seeds early so the plant grows and is almost or at maturity before this stopping period. You want the plant to be mature before the Persephone period. Later in the winter/early spring when daylight increases, the plant will resume growth.
mache
Also, find out the best temperature range for seed germination (start indoors versus outdoors), keep the seeds moist if starting outside in the hot, dry summer, and learn each crop’s tolerance for cold (soil and air) to know if you should provide additional warmth with row covers, cloches, or hoop tunnels in the winter. As the plant matures and frost comes, you may want to cover some crops to keep them alive during the winter and to harvest during the winter.
Even though it is still summer, start your cool season veggies now so they have time to mature before the day length is too short. You can always provide a little more warmth with coverage but you cannot control the day length. Below are handouts from Virginia and Maryland extension offices as well as a local seed company.
Virginia Cooperative Extension
Vegetable Planting Guide and Recommended Dates
University of Maryland Extension
Southern Exposure Seed Exchange
Southern Exposure Seed Exchange is a Virginia-based seed company that also has very useful local information: Fall and Winter Gardening Guide
