When to Start Fall Seedings
Don’t Start Too Late
A common mistake is to start fall seedlings too late into the summer prior to outdoor planting time. You should time seed sowing against the expected date of the first frost in the fall. You can often get these frost dates from any quality independent garden center. Gardeners with experience in growing seedlings in the spring are often likely to make this mistake of being late. Spring seedlings are planted at a time when the days are getting longer and warmer, allowing them to reach maturity as expected. The summer seedling is planted at a time when the days are getting cooler and shorter, so the growth rate of most plants slows down and therefore take longer to reach maturity than is noted on the seed packet.
You need to consider two pieces of information to find the right time to plant summer seedlings- maturity rate and period of performance or production. You need to know the projected maturity date for the plant you are working with. That information will always be on the seed packet for the spring seedlings. You should then extend that stated period by about 25% to adjust for the slower fall growing pace. If a brocolli has a printed days to maturity of 65 days, you calculate 25% of that period (14 days) and add that to the period to get your fall projection (65 plus 14 is 79 days.
For flowers that performance period is how long it will stay in bloom and look great. In most cases that would be three to four weeks for annuals and about a week or two for perennials. For vegetables, the harvest period is usually a few weeks.
The date to plant the seed then is the number of days for fall maturity plus the number of performance days subtracted from the date of expected first frost. Now for some vegetables like cabbage or broccoli, you can pick past the first frost, so you make an adjustment in your calculation.
In most cases, for flowers and vegetables, you are probably starting seedings June and early July.
Containers for Seedlings
Unlike in the spring, you have a choice to plant your seed inside in containers or outside directly into soil, or outside in containers. While for some plants, outside planting may have some advantages, we strongly recommend starting fall plants indoors in containers. The primary reason is that the basement is not likely to go above 75F while the outside temperatures might be in the 90’s in July and August – not good temperatures for seedlings.
In choosing a container for your seedlings, consider not only convenience but also how much damage might occur to seedling roots at transplant time. If roots are torn or broken during transplanting, otherwise healthy seedlings may stop growing while they recover from their injuries. To make transplanting less of a shock to plants, choose individual containers for seed starting. Seedlings can be started in everything from styrofoam coffee cups (which are free from the office waste basket) to peat pots purchased from the local garden center. While we would never discourage personal creativity and ingenuity, our advice if you are a beginner in this seed starting business, go with the commercial products. You can choose from individual containers to seed starting systems that have space for 15 or 20 plants.
Individual containers – If you are starting more than two dozen plants, we recommend what are called Jiffy 7’s. These are disks, made of peat moss, about the size of a fifty cent piece but a little thicker. When you place them in water, they expand into a uniform seed starting material a little smaller than a tennis ball. These devices can be planted directly into the ground, thereby reducing any serious root disturbance from transplanting. If you are starting only a few plants, then we prefer what are called “peat pots”. These are containers made of peat moss and come in various sizes from about 2 inches high to as big as a water glass. You fill them with a planting material and when the seedling is ready to put outside, you plant the pot and all. The peat pot breaks down and adds organic material to your soil.
Seed Starting Systems – There are any number of seed starting systems on the market. They come as small as holding just 6 plants, to bigger ones holding as many as 36 plants. The better systems have clear covers making them into a mini-greenhouse that holds the moisture and humidity inside which is good for seedlings. These systems almost always have some kind of convenient watering feature, making it less likely that your seedlings will dry out to quickly. We recommend these systems most for gardeners who intend to transplant their seedlings at least once into a larger container before setting the plant outside.
If you do not use Jiffy 7’s which serve as their own containers, you will need some growing material to put inside your container. Major Rule – Never use soil from outside to start seedlings; ever. That soil has all kinds of potential disease problems for vulnerable seedlings. You are looking for what is called a "soiless mix". ”Such a material is sterile, and free from disease problems. It is also a material that drains well while simultaneously retaining moisture. You can buy soilless mixes designed especially for seed starting from any garden center. If you wish to make your own, a standard recipe is one part vermiculite, one part perlite, and two parts commercial compost or commercial potting soil.
Light for Seedlings
Seedlings grown indoors often get spindly because they don't get enough light. You can start seedlings on a windowsill of a south-facing window or in a greenhouse, but in late winter, the days are still relatively short, so there is not really enough light to produce compact, healthy transplants. Seedlings raised on the windowsill will always be spindly compared to those grown in the South someplace and shipped north for sale in a garden center.
The best seedlings are grown under fluorescent lights. They give enough light to produce healthy strong stalky seedlings with very little trouble. For most people, just one shop light fixture with two 48-inch fluorescent tubes is sufficient to get started raising seedlings. Be sure the fluorescent light fixture is adjustable so that you can move it either up or down, or you have to figure out ways to move the plants up and down. You'll need to maintain the proper distance between plants and light as the plants grow. Standard bulbs will do an acceptable job, however, you can buy special fluorescent bulbs designed expressly for growing plants indoors. These bulbs will be a bit more expensive, but the results are obvious in terms of healthy seedlings.
The basement is an ideal location for setting up a fluorescent light for starting seedlings. The temperatures are usually more constant in a basement, keeping between 60F and 75F throughout the whole year. Most basements have water available, which makes caring for the seedlings convenient. Folks without basements might consider building a seedling bench that harmonizes comfortably with the other houseplants in the living room.
The keys to successfully growing seedlings under lights are the duration of light and the distance the light sits from the top leaf of the plant. Have your lights on for 14 to 16 hours a day, every day. Anything less will not produce the best growth. Use an automatic timer to turn the lights on and off. When seedlings are just little sprouts, hang the lights no more than 3 inches above. As the plants get their first true leaves, move the lights up to about 4 inches above those leaves. You can set the lights at 6 inches when the seedlings are several inches tall so that the light shines evenly on all the plants, even those on the edge of the shelf.