Extend the Harvest
by Sowing Seeds in Summer

Careful timing ensures a good harvest before winter arrives

broccoli

To harvest a fall crop of broccoli, you need to find out when hard frost usually comes to your area. With that date, you can plant accordingly.

By Sophia Bielenberg

Head of broccoli

PLANTING fall crops is a great way to get the most out of your garden space and increase your harvest. With just a little planning, you can extend the harvest long into the fall and even winter. When the cooler weather arrives, you’ll be glad you planned ahead. Growing in the late summer and fall also comes with some major perks, including fewer problems with pests and diseases. Depending on where you live, however, the window for sowing fall crops can be short, and it’s really important to start on time for an abundant harvest. In this article I’ll offer a few tips to help plan your fall harvest.

Growing in Spring vs. Fall

Planting in spring is quite different from planting in summer. In spring, you’re planting into cool soil that is getting warmer, and the days are getting longer. But in summer, you’re planting into hot soil, and the days are getting shorter (and eventually, colder). This means that crops planted in summer will grow more slowly and take longer to mature than spring-planted crops. The difference is so marked that you need to add a “fall factor” — about two weeks — to the time it normally takes a crop to mature.

Light Frost vs. Hard Frost

A light frost occurs between 29 to 32 degrees F. and will only kill tender plants; a hard frost occurs when temperatures drop below 24 degrees F., which will cause severe damage to most vegetable plants.

The other big difference is that spring-planted crops must be protected from any stray late frosts. But with many fall crops, there is essentially a “hard stop” on the season: your first hard frost date. (If you don't know the hard frost date in your area, check The Farmers Almanac.) Many fall crops, such as broccoli and kale, are frost-tolerant or frost-hardy, and will actually improve in flavor and quality after a light frost. But growth will slow dramatically after frost, especially a hard frost. The goal is to have fall crops that are nearly mature by hard frost.

When to Sow: An example

Here in northern Vermont, our first frost happens around Sept. 30—but this is usually a light frost, and we aren’t likely to have a hard frost until around Oct. 15. Because our frost-free growing season is only about 125 days, it’s extra important to get fall varieties started on time. Broccoli is popular here as a fall crop, because the quality is much better than in the spring. In order to figure out when to start, we need to do some math:

30 days from seed to seedling
+ 65 days from seedling to harvest
+ 15 days "fall factor"
= 110 days from seed to harvest.

So, to harvest mature broccoli by Oct. 15, we need to sow seeds by the end of June at the latest.

Spinach

Spinach

Fall Crops to Start Indoors
from Seed

The following crops should be started indoors in summer so you have beefy transplants. In general, they should be planted outside no later than two months before the first hard frost in your area. In some areas, you can buy seedlings at a garden center so you don't have to start your own from seed.

Crop When to start indoors (before planting out) When to plant out (before first hard frost) Days to maturity (from seeding, including "fall factor") Your average first hard frost date
Click to find the date in your area.
Fall harvest window
Broccoli 4 weeks 11 weeks 110 1-2 weeks
Cabbage 4 weeks 12 weeks 120 3-4 weeks
Cabbage, napa 3-4 weeks 10 weeks 100 2-3 weeks
Cauliflower 4 weeks 12 weeks 120 1-2 weeks
Kale 4 weeks 8 weeks 85 2-3 months
Kohlrabi 4 weeks 10 weeks 100 1-2 weeks
Lettuce, head 3-4 weeks 8 weeks 85 1-2 weeks
Radishes

Radishes

Fall Crops to Start Outdoors
from Seed ("Direct Seeding")

The following crops should be sown directly in the ground on a regular basis so that they’ll be continuously available through the fall. This is called "succession planting." For best results, the final planting or "succession" should be sown no later than two months before the first hard frost.

Crop When to sow (for continuous harvest) Tips
Greens: salad mix, baby lettuce, Asian greens, mustards, claytonia, cress, beet greens and spinach Every 1-3 weeks May be cut 1” above soil line and allowed to re-grow for a second harvest
Roots: carrots, beets and turnips Every 2-3 weeks Cool hot soil by covering with cardboard for 3 days before sowing
Scallions Every 2-4 weeks May survive winter into the following year
Radishes Every 10 days Fast crop, may be mixed with carrot or beet seed to mark rows
Cilantro Every 2-4 weeks Coriander may be collected when plants go to seed
Sophia Bielenberg

Sophia Bielenberg is an avid gardener and has been working at organic farms and nurseries as well as taking pictures of (and writing about) plants for over a decade. She is a writer, producing content for the blog, catalog and social media at High Mowing Organic Seeds in northern Vermont. She is passionate about plants and traveling, which allows her to see all the strange and wonderful species that enrich our planet. She especially likes to grow kale, tomatoes, succulents, potted citrus and Venus fly traps (which produce beautiful flowers if you're patient!)

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