Almost a year ago I promised a post on low-cost, low-resource ways to start and grow any seeds that you have determined will do better with an early start under controlled conditions. Now that seed starting time is approaching for those of us who garden in the St. Louis area or other places with similar climates, here is that post, the first of however many it takes me to give you the information I would have liked to have when I began.
I’ll be starting onion and leek seeds this week (crops I didn’t discuss in my earlier post on direct sowing versus starting seeds inside, but they are also good candidates for indoor starting and transplanting because they take a long time to sprout and grow and need to be planted early to grow well, in late March to early April around here). Some other seeds, such as cabbage family plants, can be started within the next few weeks. So purchase your seeds if you haven’t already, and start collecting materials you’ll need for growing them.
In order to start seeds early, you need these things (besides the seeds, of course):
1. A suitable environment in which to grow them;
2. Soil or a soil-like medium in which the seeds can germinate and grow; and
3. Containers to hold the soil and seeds that will fit into the environment in which they will grow and not cause damage to anything you care about in that environment.
I will deal with each of these in turn, emphasizing using what you already have on hand or can obtain free or at low cost. This post discusses the environment seeds need. I’ll discuss the next two issues in the next post, planned for later this week (if needed I will continue into a third post next week).
A suitable environment is one which can be kept at the temperatures at which your seeds germinate and/or grow best (these are not necessarily the same), has sufficient lighting for good seedling growth, is not damaged by water leakage from the containers, and is easy for you, the gardener, to work in. Very generally, you want an area that you can keep above freezing and not so warm it cooks your seeds or plants (40F to 90F works for most seeds and seedlings; some seeds need 70-90F to germinate but the seedlings grow best at somewhat lower temperatures), is lit brightly by sunlight or artificial lighting, and is protected from water by some means or will not be damaged by leaking water.
If you want to start seeds early and you don’t have any space except a windowsill, first make sure that you have a suitable window. Seedlings need a lot of light to grow well; that means a south facing window or at least whatever window faces most nearly south that you have. That window should not be shaded by outside plants and you should be willing to not cover it during the day. If your windowsill is very narrow, place a shelf or a small table (a tray table works well) next to the window that extends out from the window about two feet at most. Any farther from the window than that will not have enough light to grow seedlings well. You’ll want to turn your seedling containers every few days to keep your seedlings growing as close to straight up as possible, otherwise they will lean in toward the window and their stems will elongate as they grow. They won’t grow as stocky as will plants grown on a sun porch or in a cold frame because of the dimmer light even a south facing window has, but they will do OK. Since your south facing window real estate is limited, decide what is most valuable to grow as seedlings based on your gardening goals and what will do best in the conditions inside your living space. Often this will be tomatoes. They are a good choice for windowsill growing because you don’t need many plants to get a lot of tomatoes, they grow well inside most peoples’ homes in March and April, and you have a much wider choice of varieties available from seeds than from started plants. However, you can as easily start lettuce or cabbage or many kinds of herbs or annual flower seeds, for example, on your windowsill. Make sure that any water draining from the containers will not damage the windowsill or any extensions out from it and water the containers as needed. You’ll need to harden off the seedlings (acclimate them over a week or two to outside conditions by putting them outside for an increasing number of hours each day, then bringing them back inside for the rest of the day) before planting them. If you don’t, they will sunburn and dry out in the wind and may die from too-rapid exposure to harsh outside conditions.
If you want to start lots of different kinds of plants from seeds, you will likely need more space than a south facing window provides. If you have a glassed-in porch of which the longest wall faces anywhere but north, you have an ideal setup to raise a lot of high-quality seedlings. Most such porches will stay within the 40F-90F range without your attention during March and April except on the warmest days when you will probably want to open up the porch anyway. (If you do open the porch windows, be sure to close them again at night if the temperature will drop below freezing!) To start seeds like peppers that need more constant warmth than a sun porch provides in winter to early spring, you will need to use a heat mat. A heat mat is a rubber or plastic sheet with a wire embedded in it that is connected to a plug; electricity traveling through the wire heats up the wire and thus the mat. Containers with seeds are placed on top of the mat so they are heated from the bottom. A heat mat requires a fair amount of electricity (though much less than heating the whole porch!) so you will want to limit its use to just those seeds that most need the extra warmth for good germination (peppers, eggplants, maybe tomatoes, and certain herbs and flowers) and just during the time that you are germinating the seeds as the seedlings prefer growing on at ambient porch temperatures. Keep an eye on all the containers, especially any containers on a heat mat, to make sure they stay moist enough, and water as needed. If you are just beginning to raise plants from seeds, choose one or a few types of plants to try while you work out your system. If your porch has large air leaks to the outside, fix those before starting seeds so you can keep the environment more constant. Your plants will do better the closer you position them to the glass, but you won’t need to turn your plants often if at all and you can grow farther back from the windows than two feet because most porches have a lot more light entering than does a lone window. If you open your porch windows when it is warm enough, your seedlings will not need to be hardened off. Now that I have a south facing glassed in porch, I start almost all seeds on it except for the ones that need exposure to winter conditions to germinate.
If you don’t have a porch but you do have a reasonably flat and sunny space outside, you can build a cheap and effective cold frame for starting seeds. A cold frame is a bottomless box on which the top face is angled away from the horizontal (the north end is taller than the south end to catch low-angled early spring sunlight) and covered with glass or plastic. The cold frame becomes quite warm on sunny days and stays warmer than outside conditions at night. Below is a picture of two cold frames we used to have. Our current cold frame is located behind our garage and is about the same size and shape as the front frame in the picture.
To use a cold frame, put it down on the ground or on whatever other bottom surface you have, put your seed-starting containers inside, and cover the openings with glass or plastic or window screen as needed, held down against the wind. The pictured cold frames sat on the ground in our back yard. Our current frame sits on a blacktopped area behind the garage. I prefer the blacktop because it holds heat better and doesn’t get moles tunneling under it or have as much insect or disease pressure as might be the case for a frame sitting on the ground, but either way works. You’ll cover the frame with glass or plastic for growing most seeds, but if you are starting seeds of native plants that need cold, moist conditions to germinate, cover them with screens like the front cold frame in the photo and start them by early January. You should monitor the cold frame daily (unless you are growing native seeds under screens during winter; you can leave them alone until warm spring weather dries the seed starting medium enough to need watering). The need for daily monitoring is the biggest disadvantage to a cold frame covered with glass or plastic. On sunny days such a cold frame can get very hot, up to 100F or higher, if you don’t ventilate it. Temperatures that high will kill seeds and seedlings. To ventilate, I push heavy windows like those shown on the rear frame either up or down a few inches to expose some space at the top of one or more openings and at the bottom of one or more, which allows cooler outside air to enter at the bottom and warmer inside air to flow out the top. Or I remove the windows entirely and cover the openings with screens. Or I prop up either the low or high end of the window to leave space for air circulation. You will find ideas for props in cold frame design publications. You must pay attention to the weather and replace the windows before the outside temperature drops below freezing! It’s best to replace the windows before sunset but it can be done afterward. Usually by early April it is warm enough most of the time that I replace the windows with screens except when the occasional below-freezing night is forecast; in that case I put on the windows at night and take them off the next morning. I also cover the cold frame with a tarp to keep heat from radiating out through the glass. The other thing you need to monitor is the moisture level of the growing medium; water as needed for the kind of plants you are growing. Sunny days that heat up the inside of the frame will increase your seedlings’ need for water. Currently I move seedlings from the sun porch to the cold frame as I prick them out into individual cells of a cell pack or into small pots. In this way I can control the environment better during critical germination and early growth periods, moving seedlings to the frame when they can better take the more changeable conditions in the frame and leaving room on the porch for other plants and seeds.
If your garden space grows beyond what you can plant with seedlings grown on a windowsill and you don’t have a suitable porch or space for a cold frame, using artificial lighting in a basement or spare room to grow seedlings can make sense. To do this cheaply, purchase or salvage a 4 foot long fluorescent shop light (far cheaper than the specialized lights the fancy garden catalogs sell for the purpose). Use one warm fluorescent tube and one cool tube in the light; the combo gives light close in quality to the expensive grow light tubes and costs a lot less. Plug the shop light into a timer and set the timer to keep the light on for 16 hours each day. Suspend the light over a table or shelf about 4 feet long and about 2 feet wide, the largest area one light can illuminate well enough to grow seedlings. We hung two lights on adjustable chains from the basement ceiling and put an old, fake wood rectangular dining room table covered with two 4 foot long and 2 foot wide trays (the kind sold for the very expensive grow light systems for sale in garden catalogs; you might be able to find or make something similar for less money) under the lights. You need to adjust the height of either the light or the plants so the plants are within a couple of inches of the light as they grow. You also want to protect the surface of the table or shelf from leaking water, hence the trays, and to supply the seeds and seedlings with the temperatures they need. In our unheated basement I could only start seeds preferring cool conditions to germinate without using a heat mat to heat the bottom of the containers. Those mats suck up a lot of electricity, as do the lights, so you will want to start no more seeds than absolutely necessary in order to minimize the material and electricity cost. You will need to harden off all the seedlings you grow under artificial light as described for growing seedlings on windowsills, and the seedlings will not be as healthy as seedlings grown on a porch or in a cold frame. I no longer start any seeds under artificial light because I have a porch and a cold frame that produce much healthier seedlings and lots more of them. But before I had either I started seeds under artificial light because I had insufficient window space for starting them.