Posted: July 22, 2025
Fall vegetable gardening is often referred to as the second spring.
A December snow did not stop a good harvest of veggies from the author’s garden
As I’m writing this, a stubborn 'Bermuda High' has locked in high temperatures and humidity. As for rain, some of Adams County has had quite a bit of rain, while my corner barely received enough. I'm ready to think about planting for fall.
And like me, you are probably looking forward to the relief of fall weather – and crisp lettuce and sweet carrots, too! Fall vegetable gardening is often referred to as the second spring. It's getting cooler, but in many respects, the environmental factors the fall gardener encounters are opposite those for spring.
In the spring, soil gets warmer, while in the fall, soil temperature decreases. The sun moves higher in the sky until the summer solstice, and shadows become shorter. In the fall, the sun isn't as high, and shadows become longer. The hours of sunlight decrease once we're past the summer solstice, so that plants started later in the summer need more time to mature. Another 'bug-a-boo'? Many insect pests are into their third and fourth generations, unless helpful beneficial insects are keeping them in check.
Let's think about our fall favorites and how growing vegetables in the fall differs from growing them in the spring. Cold-season vegetables have some features that help them tolerate cooler temperatures. Have you noticed that kale and broccoli have thicker leaves than squash and peppers? Kale and similar brassica family plants have leaves that are trying to retain heat, while heat-tolerant plants have thinner leaves, often with jagged edges, allowing some heat loss.
Hairs are found on the leaves of some summer plants to help prevent water loss from the leaves that are feverishly cranking through their photosynthesis reactions. Since part of the photosynthesis process relies on carbon dioxide getting into plant leaves through open leaf pores called stomates, water is often lost, too. Some heat-tolerant plants, like corn, crabgrass, and many succulents, have physiological tricks to prevent water loss.
But to stand up to freezing, cold-tolerant plants have thicker leaves and thick-walled cells that are less likely to break as the cell fluid freezes into sharp ice crystals that cut the leaf cell walls of most summer vegetables. Cold-tolerant plants have another trick up their petioles, too. The molecules of starch and some polypeptides in the cell fluid break apart into simple sugars and amino acids as temperatures decrease. As the number of individual molecules in the cell solution increases, the higher solids content acts as an antifreeze. The upside from the perspective of the gardener is that many cold-season vegetables taste sweeter!
Let's talk about how to adjust spring gardening techniques to fall environmental conditions. To help the gardeners figure out how to grow their plants, information is included on the seed packet or in the seed catalog that can guide a lot of your decisions. Two numbers you'll find especially useful are 'soil temperature for germination' and 'days to maturity.'
Days to maturity are based on spring planting. Since the days are getting shorter through the fall, the number of days from planting to harvest needs to be increased by a week for quick-maturing crops and longer for slow-maturing crops. To calculate when to plant your fall crop, take the average first frost date (October 29-November 15 for us in Zone 7a), and work backwards on the calendar for your starting date.
If you are growing Gypsy broccoli, for instance, take the listed 65 days for maturation, then add 10 days for decreasing daylight. Counting back from October 17 tells you to plant it by August 3. The number of days to maturity is the same whether you are putting a seed in the ground or starting with a transplant.
This brings up an important point. Sowing seeds directly in hot, dry August soil is tricky. Pay attention to the recommended soil temperatures for seed germination found in the seed catalog or the seed packet. Note that this is a range, and that poor germination often occurs at both extremes of the range listed.
Most of the spring vegetable plants we want in our second spring plantings prefer cool soil temperatures for germination. Many lettuces germinate best in cooler soil, 40°F-80°F. Broccoli and most of the rest of the Brassica family germinate best in soil temperatures 55°F-75°F. Mustard and Chinese cabbage like lower temperatures. That means better success if you sow them indoors and set them out as transplants. Checking the days to maturity, you need to do this now.
Yes, it's getting late to start some veggies indoors, but fortunately, these are the same plants that like it cold and laugh at the first frost. In fact, many varieties of cold-hardy winter plants can tolerate temperatures down to the mid-20s or lower. Some cold-loving vegetables with long growing requirements are Brussels sprouts, some tight-headed cabbages and carrots. Lettuce, beets, and parsnips usually don’t hold long into the winter in our climate.
Check online resources for the cold tolerances of vegetables. My favorite is a blog by Pam Dowling of Sustainable Market Gardener, who reports on winterkill temperature trials for different varieties of winter vegetables each spring.
Another point when considering daylight is how long your vegetables are getting direct sunlight. Most leafy vegetables need 6-8 hours of sunlight; other vegetables want more. Maybe your garden had plenty of sunlight in April, before the neighboring trees leafed out. Will they be in the shade in October?
Keep your row cover handy, too. As I mentioned, insect pest pressure is higher in the fall than in the spring. And row covers also provide a few degrees of added warmth – and a few added weeks in some years – to your fall garden. Plastic sheets can be used to make 'low tunnels,' allowing for an even longer growing season, but care must be taken not to cook the plants. Even on a bitterly cold and windy day, the sun could heat low tunnels too much. They need to be opened to prevent overheating.
A good resource on cold-season gardening to check out is the Penn State Extension fact sheet Season Extenders and Growing Fall Vegetables.
The Master Gardener Hotline is open Monday, Wednesday, and Friday from 10 a.m. to 2 p.m. Please send an email (with pictures, if possible) to adamsmg@psu.edu with your gardening questions or stop by Penn State Extension, 670 Old Harrisburg Rd, Gettysburg.
Interested in becoming a Master Gardener, or learning more about the program? Contact Mary Ann Ryan, mar35@psu.edu, for more information or an application.
