In the previous post I discussed how you can create a good environment for growing seedlings in a number of different ways, with attention to how to do this using no or a minimum of fossil fuel energy. In this post I will look at appropriate growing media (soil or a soil-like mix) that will allow you to grow the strongest seedlings you can.
You might think that the best medium for seed-starting would be the soil right outside your door (if you own the property and can legally dig up that soil, of course). The advantage to using soil is that it is free and costs only your own energy to dig it up. Presumably it is already growing something, or did so at one time, so it should be able to grow the seedlings you want. And that might be true if you have a very light, loose, fertile soil. However, most of us, myself included, find that soil straight from the yard does not work well in containers; it is too heavy and often is not fertile enough. For those of you who have not grown seedlings before, another disadvantage of using soil is that it harbors lots of seeds of various kinds of plants already in it - you may call them “weeds” - that are as happy or more so to germinate as the seeds you planted. You may find it difficult to determine which are the seedlings you planted and meant to grow from the forest of others that pop up.
If you have not grown seeds before, or if you have but you cannot obtain the materials mentioned below for homemade media, I suggest you stick with the seed-starting media that are available for sale through a trusted local garden center or through a good mail-order site like those I have mentioned in previous posts. These media are formulated to work well in small containers and they harbor very few, if any, weed seeds. The lack of weed seeds is the major reason I recommend them to new seed-growers. Buy only as much media as you need and change over to a homemade mix once you are confident that you can recognize the seedlings you want to grow. With the commercial seed-starting mixes you will need to pay careful attention to the proper moisture level in the mix. Some of them are very difficult to re-wet if they should dry out. (If this happens, put the container in a larger container of water that comes almost but not quite up to the top of the mix, and leave the container in the water until the mix is moist again.) Also, it is best to purchase seed-starting media as opposed to a mix formulated for potted plants. Seedlings have somewhat different needs than established plants. Some seed-starting media may not have high enough nutrient levels to sustain seedlings for several weeks, so you may need to water occasionally with a dilute solution of (preferably organic) fertilizer. The better mixes may not be an issue in this regard. Check the label and ask garden center staff or the staff of your favorite mail order company what they recommend in this regard.
Once you are confident you can recognize the seedlings you mean to be growing, whether from having grown them before or from photos (search using a phrase like "picture of tomato seedlings"), and if you have access to the needed ingredients, you can make your own seed starting mix for free. At a minimum, you need well-made compost. By well-made compost, I mean compost made from a reasonable mix of dry, highly carbonaceous materials like autumn leaves or paper and wet materials like fresh grass clippings, food scraps, or garden weeds. The compost should have aged enough that you cannot recognize the individual materials that went into it and and it should have an earthy smell. Any good gardening book including the ones I discussed in last winter’s posts, and probably your state Extension office on the web (see here for Missouri’s), has directions for making compost if you don’t already know how to do this. Someday I might write a post on how I make compost as it seems to be good quality compost and requires little effort on my part. But for now, let’s assume you have your own compost on hand and go from there.
You can use straight compost as a seed-starting medium if you sift it or otherwise remove the large lumps. Some garden suppliers offer a screen that fits on top of a bucket for this purpose. You load compost onto the screen and push it through the screen with your (gloved) hands. The sifted compost falls into the bucket. Continue till all that is left on the screen are various pieces that are too large to go through the screen. You use what is in the bucket to start seeds and dump what is on the screen either back into the compost pile to further decompose or elsewhere in the yard where it can re-enter the ecosystem. You can fashion a sifter of your own by constructing a shallow bottomless box that will fit over a bucket or, for larger quantities, over a wheelbarrow or garden cart and attaching 1/2 inch square hardware cloth to the bottom of the box.
Although you can use the sifted compost by itself for starting seeds, it can be extended and improved by mixing it with garden soil. John Jeavons’ book discusses making seed starting media from a mix of garden soil and compost; this is the method that I use. You don’t need to double-dig to get the soil as he does; just dig some up out of your garden when you need it. You may need to experiment to find out how much garden soil you can mix with the compost and still have a light enough material to work well in small containers. We have a silt loam soil and I find the best mix is about two parts compost to one part soil. If you have a clayey soil you may need to use a higher proportion of compost. If you have a very light sandy soil you may find a higher proportion of soil works better. I keep large plastic containers of garden soil and sifted compost in the basement, where they will be unfrozen in winter when I begin making seed-starting mix. To make the mix, I measure out the components into a bucket, using a plastic cup as the part measure, and mix them together in the bucket, using my hands and a cultivating tool that fits in the bucket to get the components as thoroughly mixed as possible. I don’t sift the soil because we have so few rocks in our soil as to not be an issue; you may find you need to sift the soil as well as the compost to make a non-lumpy mix. I do remove any sticks, rocks, and other debris that I see and crush big lumps of soil before and while mixing.
Before I had a worm bin, I made all of my seed starting mix with only compost and soil. Plants like lettuce and cabbage that don’t need a highly fertile soil did well enough in this mix. Tomato seedlings, however, grew quite slowly and had a purplish cast characteristic of lack of phosphorus. Because worm castings are high in nitrogen and phosphorus, I started adding them in small quantities to my homemade seed-starting mix. It made a big positive difference in tomato and pepper seedling health and growth. If you have access to homemade worm castings, use it in your seed starting mix (it’s worth keeping a worm bin going if you grow a lot of seedlings or container plants so you always have a free source of castings). A good ratio is one part of worm castings to a total of 8 to 12 parts of other ingredients; worm castings can burn your plants in too high a concentration. If you don’t have enough castings to make sufficient mix for all the seedlings you want to start, add castings to only the mix for plants that need a lot of nutrients to grow well (for vegetables, this includes tomatoes, peppers, and eggplants, probably okra as well). Some garden centers sell bagged worm castings if you don’t have your own and find that your seedlings need the nutrient boost.
Looks like I had enough to say on media that I need to make a separate post on containers. So be it; I’ll plan to write that post over the next week.