Your deadline for late seeding in fall depends on your first frost date and which crops you plan to grow in your garden this year. Hardy crops give you more time since they handle cold snaps and light frosts well. Tender crops need earlier starts or they die at the first sign of frost in your region.
I tested my limits with fall seed starting two years ago by pushing broccoli starts into early September. They never sized up before my November frosts hit because I started too late in the season. Now I count backwards from my first frost date and add 10 to 14 extra days as a buffer for slower fall growth.
In my experience, fall plants grow slower than spring ones because daylight hours shrink each week after August. USU Extension data says to add time beyond what seed packets suggest for this reason. Your autumn planting schedule needs to account for this slower pace or you end up with small plants at frost.
Hardy vegetables like kale, spinach, and Brussels sprouts handle brief dips below 32°F (0°C) without damage to their leaves. These tough crops let you seed later in fall and still get a good harvest before winter locks your garden down for the season. Some even taste much better after light frosts convert their starches to sugars in the cool air.
Tender crops like beans and squash face damage when temps drop below 50°F (10°C) at night in your area. USU Extension says these warm-season vegetables die fast once cold hits your garden beds hard. Skip them for your fall seed starting plans unless you have a heated greenhouse to keep them safe and warm all season.
Start broccoli, cabbage, and lettuce indoors 8 to 10 weeks before your first frost for the best fall results. These crops thrive in cool autumn weather and keep growing well into November in most zones. Move them to a cold frame after frost hits and you can harvest through December or January in many areas.
Check your local extension service for the exact first frost date in your specific county or zip code area. Mark that date on your calendar and count backwards to find your last safe day to start fall seeds indoors at home. Give yourself extra time rather than cutting it close since late starts often fail to produce anything useful for your table.
Read the full article: When to Start Seeds Indoors: Ultimate Guide
