Squeezing in one more round of planting and harvesting from the garden is a great idea. That way, you can have fresh garden salads, aromatic herbs, and a few colorful flowers until a fall frost takes them out. Ideally, you’ll have planted your fall garden in July or even August.
But maybe you didn’t get around to planting in August. Or even September. Perhaps it’s already October, and you’re thinking about throwing out some seeds and seeing what happens. It’s a nice thought, but unless you live in a warm climate, chances are you’re planting too late to have much success.
Planting seeds too late in the year will result in poor or no germination due to cold soil temperatures, too much moisture, or insufficient sunlight. Seedlings planted too late in the garden will also be slow to grow as the days shorten and sunlight becomes more limited.
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How late is too late to plant a garden?
In colder climates, gardeners should plant their seeds by the end of August for a fall harvest. If your region has mild winters, you may be able to get away with planting in early October as long as temperatures remain above freezing.
Vegetables like collards, kale, spinach, turnips, radishes, and herbs like parsley and thyme will perform well in cold weather. Flowers such as calendula, snapdragons, and scabiosa can take temperatures down in the 50s as long as they’re established.
If it’s already October and you still want to give planting a go, focus on crops that can tolerate cooler temperatures, and be sure to use transplants rather than direct sowing.
1. Cold and wet soil will hinder seed germination
Soil temperature is one of the most critical factors in germination rates, right up there with adequate moisture. If the soil is too cold, a seed will not germinate. Even cold-weather crops like kale or spinach germinate best when the soil is at least 60 degrees Fahrenheit.
Germination rates will be poor if the fall season has progressed enough to cool the soil to less than 50 degrees Fahrenheit. Those brave seeds that germinate anyway will grow much more slowly than if they were in warmer soil. Slow germination combined with slow growth does not spell success for seeds planted too late in the fall.
To complicate matters further, if you’re directly sowing these seeds in the garden, you also need to know how much rain you get in your area as the year winds down. Some places will experience cooler weather while staying relatively dry. For other regions, fall means that cool temperatures and the return of rain go hand in hand.
If you live in a cold and wet climate, you will have to contend with soggy soil, which can lead to the seeds rotting in the ground before they even get a chance to sprout. Heavy rains can wash away your carefully sown seeds. It paints a bleak picture.
2. Short days will limit the growth of seedlings
You might read the paragraphs above and decide to start seeds indoors to avoid too wet and too cold soil. Fair play! Starting seeds indoors will control the soil temperature via seedling mats and the moisture via regularly scheduled waterings.
But keep this in mind:
Seedlings planted too late in the season face increasingly fewer hours of sunlight as the days grow shorter. Without enough sunlight, the seedlings will sit dormant over the winter, waiting for spring to return with longer days before resuming growth.
This next bit might bring back dim memories of middle school. But here’s why your plants will go dormant as fall winds down to winter.
Sunlight is essential to plant growth. It allows the plants to photosynthesize or make food for themselves. Different plants need different amounts of sunlight to grow. That’s why some plants can thrive in partial shade, like lettuce, while others, like tomatoes, need full sunlight to reach their potential.
Seedlings need at least a full day’s worth of sunlight, ideally 14-16 hours per day, to ensure healthy growth. A late fall-sown seedling will probably get only 8-10 hours of weak sunlight per day. It doesn’t take a math whiz to know that eight hours is half the ideal 16 hours.
To avoid waiting too long to sow, learn the ideal time to get your seeds going in this article, New To Fall Gardening? Learn When To Plant One In Your Zone.
Skip fall sowing and jump to winter sowing
Alright, it’s time to shake off the doom and gloom of what happens if you plant seeds too late in the fall. You can use winter sowing to still get some seeds in the ground this year, but you will have to wait until the following spring to see any growth.
Winter sowing means sowing seeds outdoors that need a period of cold to germinate, typically in January or February. The seeds lay dormant in the soil, then sprout when the temperatures and day length increase. Plants such as broccoli, peas, rudbeckia, and foxglove can be winter sown.
Most gardeners winter sow their seeds under some protection, such as an old milk jug or in a cold frame. This way, the seeds don’t get as saturated as those exposed to all the winter rainfall, and they won’t wash away. The jug or cold frame also acts as a mini-greenhouse to warm the soil faster in the spring, helping with germination rates.
Flowers, in particular, respond well to winter sowing. With this method, you can get a head start on having blooms in your home garden. To see first-hand how it’s done, Tonya of FreshCutKY has a very helpful video explaining her winter sowing method. Check it out here to follow along: