I put together a youtube video to give you a visual and audio explanation of seed starting basics. Below it, I will outline supplies and procedure for reference.
A good quality potting soil is recommended. It doesn’t have to be specifically “formulated” for seed starting, just not too chunky. Anything that I have purchased in a bag has been of acceptable texture. I purchased some potting soil in bulk once that ended up being much too chunky. It was intended more for repotting larger shrubs. The quality of the potting soil matters because the lower quality types tend to get hard when they dry, much like regular dirt from outside does. It can be very hard to get such soils to reabsorb water after they have dried past a certain point. Exact color doesn’t seem to matter, although most of them will be a pretty dark brown. The common wisdom is that darker soil is healthier, but I have tried to use darker bagged potting soils that were less expensive and ended up not working well.
Of course, it is possible to make your own potting soil using a 1:1:1 mix of compost, peat moss, and something like perlite or vermiculite, but I have found it more labor intensive than I like. It is a lot of stirring.
To prepare the soil for seed starting, mix in enough water to make it the consistency of thick oatmeal. One of my guidelines is it is wet enough that just a bit of water can be squeezed out of it. If there is a little water pooling in the bottom of the bowl when you get down there, just add a bit more soil to get the correct mix again.
Although any container will do for a pot, it can be challenging to create drainage in homemade pots that is large enough holes, yet doesn’t end up breaking easily. It can also be hard to make diy pots that have a ratio of height to depth that both allows for efficient use of potting soil and easy water management. If all the water is draining to the bottom of an over long pot, it doesn’t do much good for a new seedling near the top. If you try to use biodegradable pots, either homemade or purchased, it could make it harder to repot for larger growth as the need arises. There also needs to be care taken at the time of transplanting to make sure the top edge is just below soil level, yet the plant does not get planted to low into the ground for its liking. Something like tomatoes can handle being planted higher up the stem, but not all plants can.
If you buy any potted plants, whether pony packs or larger, you can always save the pots. I have done this for years, recycling them until they disintegrate. I also have a variety of pots specifically produced for the home gardener. Most of them have lasted for years with little sign of wear, so I consider them worth the expenditure.
Choose your pot size based on how big the seedling will grow in the first 4 weeks. This will allow for space efficiency, while giving the seedling room to grow. It might make it to 6 weeks, but many will benefit from repotting past that time period. Remember, the pot confines the roots, which in turn limits access to water and ability to support top growth. If the roots get to entwined, or “root bound,” in the smaller pot, the plant may never recover.
Fill the pots with soil to about 1/2 inch below the top edge. If they are filled to the top, they will be harder to water, as the water will tend to flow off before it has much chance to soak in. Also, there is a higher risk of the seeds being washed away.
Decide which seeds it is worth your time to plant indoors. I explain some of my thoughts on this in this article 10 Criteria for Deciding Which Garden Seeds to Start Early in Your Greenhouse.
Pay attention to whether or not the seeds need light to germinate. Most seeds need about the same temperatures to germinate, although there are extremes, such as lettuce liking it a bit cooler. Some seeds take longer than others for no apparent reason. Experience has just shown they do. Some need to not be kept quite so moist, like peppers. Still, all seeds need some level of constant moisture while they are germinating because they do not have the ability to store water at first.
Planting the seeds in the soil is basically a matter of sticking them in. Yes, depth of planting generally makes a difference, but I have experimented with very loose adherence to recommendations and had good results. Too deep is usually more of a problem, but water and light make the most difference once germination has occurred. For most plants, it is just as well to plant 3-4 seeds per pot, to assure at least one plant in each pot. I will talk about thinning or transplanting another time.
Make sure to label everything as you go along, or you will regret it. It is too easy to lose track of what you planted, not only for more than one variety for a given vegetable, but also because some vegetables look a lot alike as young seedlings or don’t look enough like the mature plant to avoid confusion.
Water the pots one last time with a gentle mist after the seeds are planted. This helps the soil to settle and make good contact with the seed. They need to feel that.
I explain my “self watering” system in the video, which is good for about 3 days to a week, depending on the seeds and outside conditions. I peek inside the plastic every day after 3 days to check for sprouts. If any fuzzy white starts to grow in my pots, I take off the plastic and manually attend to the watering 1-2 times a day with a misting nozzle until the seedlings are big and sturdy enough to handle a gentle shower setting. And, again, for peppers, I have found it best to let the soil get a touch drier after 3 days.
Also, remember that any potting soil stays relatively dark, even when dry, so color is not a good way to test for moisture. The best way to learn to judge the moisture in a pot is to stick you finger slightly into the soil. I often just water thoroughly and regularly the first few days without checking much, but then I have a lot of experience with knowing how much water they will need.
I will write about care of seedlings in another installment, but at this point you should already have an idea and set-up for how you are going to give the seedlings adequate light. Rarely is a window sill good enough for satisfactory growth. My husband made me some grow light stands that may interest you, so click here to read about them!