I claim no special knowledge of growing plants from seed. I’ve done a lot of it and I think I’ve had reasonable results, but I’ve had my share of failures too.
There is an abundance of information available online about seed sowing, to the point that I wonder why I bother writing about my own methods, but maybe there’ll be something of use to someone. If I worried too much about an online abundance of information, I’d never write anything.
I sow most seeds into 9cm plastic pots. I have hundreds, all recycled. I wash them and fill them with compost. I am currently using Melcourt’s Sylva-grow, a peat free multi-purpose made from wood waste and bark. I bought a bag of their professional seed and cutting compost a couple of years back and it looked identical.
I break up any lumps in the compost, fill the pot loosely then tap it on the bench to settle it. I like to get the surface level in the belief that an uneven surface will mean uneven moisture and therefore erratic germination. I pick out any lumps, if you get two or three seedlings rooted into a lump you can’t separate them.
I then sow my seeds as evenly as possible. I usually have a bit of an idea how many of something I want and sow roughly 50% more than I need. 40-50 seedlings in a 9cm pot is as many as you really want.If I need more I sow two pots or a half tray. I then cover the seeds with a bit of fine compost and spread that out evenly before watering from above with a fine rose on the can.
Most things go onto my heated bed in the greenhouse, maintained at 20-25°C. The odd thing like tomatoes or chillies I will bring into the house and germinate at a slightly higher temperature. I don’t cover the pots but I will soon be putting shading onto the glass so the pots of seeds don’t overheat.
As soon as the seedlings are big enough to handle I will prick them off, usually into cell trays. If the roots are small I fill the tray, make holes with a dibber, put the seedlings in and push compost around the. If the roots are bigger I hold the seedling in the cell and fill around the roots with compost. I pick the strongest seedlings and discard any deformed ones.
Some things get planted directly into the ground from the cell trays, some get potted up individually into 9cm pots.
I sow a few things directly into cell trays but I never get the uniformity that I get with pricked off seedlings. There always seem to be a few cells where nothing comes up or the seedlings are weak.
Some things need treatments to break dormancy and that complicates things somewhat. Let’s not go there just now.