Fall seed starting is about two different jobs at once: sowing seeds that will grow into a fall harvest, and sowing seeds that will sit through winter and grow in spring. The first job is a race against frost, since seeds sown in late summer and early fall must grow fast enough to mature before cold weather stops them. The second job is a slow one, since seeds sown in late fall germinate slowly or wait in the soil until spring, and they need protection through winter. Both jobs reward the gardener who sows at the right time and in the right place, and both are covered in this guide.
The key to fall seed starting is counting backwards from frost and adding extra time. Plants grow more slowly in fall than in summer, because days are shorter and light is weaker, so a crop that takes fifty days in summer may take sixty or more in fall. Add about two weeks to the days to maturity on the seed packet when you plan a fall sowing, and sow earlier than you think you need to. Use our seed starting calculator to work out sowing dates from your last and first frost dates, and check your local extension service for sowing dates tuned to your area.
Seeds to sow in early fall for a fall harvest
The main fall harvest sowings happen in late summer and early fall, while the soil is still warm. Fast-growing salads are the easiest: lettuce, spinach, arugula, mustard greens and Asian greens can be sown every couple of weeks through early fall, and they grow quickly in cool weather. Our guides to growing lettuce, growing spinach and growing arugula cover these crops. Radishes are one of the fastest crops of all and can be sown into early fall, while carrots, beets and turnips sown in late summer mature in fall and often taste sweeter after a light frost. See our growing carrots and growing beets guides.
Peas sown in late summer can crop in fall in mild zones, and brassicas such as kale, broccoli, cabbage and cauliflower sown in summer and transplanted in early fall give a fall and winter harvest. Our growing kale and growing broccoli guides cover those crops. Herbs such as cilantro, parsley and dill can be sown in early fall for a fall harvest, since they prefer cool weather to summer heat — see our growing cilantro and growing parsley guides. Sow in rows or blocks, keep the soil damp until germination, and thin seedlings to the spacing on the packet, since crowded seedlings grow slowly and invite disease.
Seeds to sow in late fall for spring
Some seeds are sown in late fall to germinate in spring. This works for hardy plants that need a cold period to germinate, a process called stratification, and for plants that are sown in fall in mild zones and grow through winter. Sweet peas, poppies, cornflowers and other hardy annual flowers can be sown in fall in many zones, and they flower earlier than spring-sown plants. Broad beans and peas can be sown in late fall in mild zones for an early spring crop, though they need protection in cold zones. Garlic is planted as cloves rather than seeds, but it follows the same logic — see our fall planting guide and growing garlic guide.
Sow late-fall seeds in well-drained soil, since wet soil in winter rots seeds, and mark the rows clearly so you do not dig them up by accident in spring. A light mulch over the rows protects the soil and marks the spot, but do not mulch thickly, since seedlings need light to emerge. Do not sow tender seeds in late fall, since they will rot or be killed by frost, and do not sow seeds that need warm soil to germinate, such as tomatoes and peppers, outdoors in fall. Those are spring sowings, started indoors under cover.
Starting seeds indoors in fall
Fall is also a time for starting seeds indoors, for crops that will grow under cover through winter or be transplanted out in spring. Hardy salads and herbs can be started indoors in fall and grown on a bright windowsill or under grow lights, giving fresh leaves through winter. Our seed starting mix guide explains how to make a free-draining seed compost, and our potting mix recipe guide covers mixes for growing on. Sow in clean trays or pots, use fresh seed compost, water from below where you can, and give seedlings as much light as possible, since short fall days make seedlings leggy if they are short of light.
Damping off is a risk for fall-sown seedlings, since cool, wet compost invites the fungi that cause it. Sow thinly, do not overwater, ventilate, and use clean trays and fresh compost. Our damping off seedlings guide explains how to prevent it. Harden off seedlings gradually before moving them outside, putting them out for a few hours a day and bringing them in at night, so they adjust to wind and cold. A cold frame is ideal for hardening off and for growing fall seedlings — it gives protection from frost while letting in light and air, and our fall frost protection guide explains how to use one.
Protecting fall seedlings
Fall seedlings need protection from frost, slugs, birds and drying wind. A row cover or cloche over a bed adds several degrees of frost protection and keeps seedlings growing for weeks longer, and it also keeps birds off. Our fall frost protection guide covers covers and cloches in detail. Mulch around seedlings, keeping it clear of the stems, to hold moisture and protect roots, and water in the morning so leaves dry before night. Slugs are a serious threat to young seedlings in damp fall weather, so check beds regularly and use the controls in our slugs and snails control guide.
Birds can pull up newly sown seeds and seedlings, so netting over a bed is worth using until plants are established. Wind can dry out and damage seedlings, so a sheltered spot or a windbreak helps, and a cold frame is the best protection of all for the most vulnerable sowings. If a hard frost is forecast and seedlings are small, cover them in the evening and uncover them in the morning, since covers left on in warm daytime weather can cook seedlings. Check your local extension service for frost protection advice for your area.
Common fall seed starting mistakes
The most common mistake is sowing too late, so seedlings are too small to survive frost. Sow earlier than you think, and add two weeks to the days to maturity on the packet. The second is sowing in soil that is too wet or too cold, so seeds rot instead of germinating. The third is sowing too thickly, so seedlings compete and grow weakly; thin them to the spacing on the packet. The fourth is letting the soil dry out during germination, since seeds need steady moisture to germinate. The fifth is forgetting to protect seedlings from slugs, birds and frost, which can destroy a sowing overnight. The sixth is sowing tender seeds outdoors in fall, which will not survive. And the seventh is using old seed without checking germination; test old seed by sowing a few on damp paper before you commit a whole bed to it.
Frequently asked questions
What seeds can I sow in fall?
Fast salads such as lettuce, spinach and arugula, radishes, carrots, beets and turnips for a fall harvest, and hardy flowers such as sweet peas and poppies, plus broad beans and peas in mild zones, for spring. Check your local extension service for sowing dates in your area.
When should I sow seeds for a fall harvest?
In late summer and early fall, counting backwards from your average first frost and adding about two weeks to the days to maturity on the packet, since plants grow more slowly as days shorten.
Can I start seeds indoors in fall?
Yes. Hardy salads and herbs can be started indoors and grown on a bright windowsill or under lights through winter. Use fresh seed compost, sow thinly, and give seedlings as much light as possible.
How do I protect fall seedlings from frost?
Use row covers, cloches or a cold frame, mulch around seedlings, and water in the morning. Cover seedlings in the evening before a frost and uncover them in the morning.
Why did my fall seeds not germinate?
They may have been sown too late in cold soil, sown too deep, allowed to dry out, or eaten by slugs and birds. Old seed can also fail. Check soil temperature and moisture, protect the bed, and test old seed before sowing.