In Part One, we discussed the nature of seeds and the merits of starting seeds in quality seed starting trays and soil, and the best way to plant seeds and thin newly emerged seedlings. In this installment we’ll cover the four most important elements of producing healthy seedlings: light, warmth, moisture and nutrition. I’ll also discuss the benefits of repotting seedlings and how to harden off young plants to prepare them for life in the garden.
Plentiful, high-quality light is crucial to the proper development of young seedlings. Before you plant a single seed, take a close look at how much light the young plants will receive each day from natural sources, such as a window. If your nursery receives less than six hours of bright, direct sunlight each day, you will need to provide artificial light. This can be as simple as common fluorescent tubes suspended over the plants or as high-tech as multi-spectrum grow lights. For the home gardener, standard fluorescent lights are both effective and affordable
Start by selecting a baffle that has space for at least two light tubes. Place a “warm” light tube in one and a “cool” light tube in the other. This provides a color spectrum wide enough to produce healthy plants when combined with natural sunlight. It is important to ensure that this artificial light spans the entire growing area evenly or plants on the outer edges may suffer.
Because plants will always lean toward natural sunlight regardless of the quality of an artificial source, it is necessary to turn trays of seedlings one-quarter of a turn, sometimes as often as twice a day depending on how much natural light they receive. Turn the trays in the same direction each time, and avoid turning them more than half a turn at any one time.
Seeds sown indoors need consistent temperatures in order to germinate properly. Warm-season plants such as tomatoes, peppers, melons, squash, basil and oregano all require temperatures of around 70° F (21° C). Cool-season crops such as spinach, cabbage, cilantro and parsley require as little as 60° F (16° C) to germinate.
The safest, most effective way to regulate soil temperature is to use a heating mat. These specialized flexible rubber mats are designed to provide steady, controlled heat to the bottom of the starting tray. Some of the more expensive mats have adjustable temperature control dials, making them quite versatile.
Avoid placing germinating seed trays near wood stoves, furnaces, heaters, and even “sunny” windows expecting steady warmth. Actually, windows are some of the worst places to keep germinating seed trays because, although they may be warmed by the sun during the day, the temperatures drop very quickly at night. Steady temperatures, even if they are not ideal, are better than wildly varying ones. For this reason, many gardeners place their seed trays on top of the refrigerator to germinate. Once the seeds have sprouted, the trays can be moved to a more permanent location.
Germinating seeds need very little moisture and one of the most common seed-starting mistakes is overwatering. Waterlogged soils or mixes smother seeds, and seeds that do germinate often wind up dying from damping off. The most effective, controllable and tidy method of watering newly planted seeds and small seedlings is misting with a spray bottle.
If you purchased a seed-starting kit that came with a clear plastic dome, use it. This dome allows light into the seed tray for seeds that require light to germinate, but more importantly, it keeps the moisture in the soil from evaporating too quickly. If you are using homemade starting trays, improvise covers for them. Shower caps or clear, plastic grocery bags work exceptionally well. If you decide to use cling-style plastic wrap, be sure and leave a corner or two open just a bit so that fresh air can get inside. Once the young seedlings have fully emerged, it is vital that all coverings are removed. High moisture levels after germination can result in damping off, mold, and other problems.
Trust me when I say that it is all too easy to start a million seeds and want to keep every single plant that germinates, but doing so is a recipe for failure. So, once you have determined the number of plants you want, write that number down on a piece of paper and keep it near your starting trays to remind you.
Once the seedlings begin to emerge it is imperative to thin them early, often, and aggressively, keeping only the best of the best. Start by removing disfigured or stunted seedlings and any that germinate long after the rest have come up. These are all undesirable traits. Allow the healthy seedlings to grow for several weeks before thinning again. Once seedlings have grown their first pair of true leaves, remove all but one plant from each cell or pot.
If all of the seeds in a cell or pot germinate, keep either the first one up, or the one that is doing the best when the time comes to thin. Do not allow more than one plant to mature in each cell or pot because as the plants grow the roots will become intertwined. Not only does this make transplanting difficult, but the young plants will be forced to compete for nutrients.
Once sprouted, young seedlings grow rapidly. After several weeks in a flat, you may need to repot young seedlings so they have more room in which to spread their roots. Gently remove the seedling from the cell or flat that it is currently in, being careful to disturb the roots as little as possible. Place the seedling into fresh potting soil, burying as deep, or just a little deeper, than it was in the original pot. To help the plants recover from transplanting, keep them out of direct sunlight for a day or two and feed them with a diluted mixture of water and fish emulsion or seaweed.
Hardening off young plants helps them adjust from the very controlled environment inside your home to that of the natural conditions outdoors. Do this by slowly exposing plants to the outdoors a little each day – allowing them more and more direct sun and leaving them outdoors longer in the evening. After two weeks of this your young charges should be hardened to the natural spring conditions in the garden. For the first week of the hardening off phase, plan on moving seedlings in and out of the house or greenhouse each day. And even after you’ve successfully planted them in the garden, be sure to have some form of protection from unexpected frosts.
Starting seeds indoors is a fun and very rewarding hobby that can save you a ton of time and money. It’s a great activity for the kids or grandkids and helps the rest of us scratch that gardening itch. I hope you will give seed starting a try… you won’t be sorry you did!
Jill Henderson is an artist, author, and the editor of Show Me Oz.
She is a life-time organic gardener, seed saver and naturalist. Her books, including The Healing Power of Kitchen Herbs and the Garden Seed Saving Guide, can be found in our bookstore.
Copyright Jill Henderson 2011
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