Like many people here in the UK I’ve been sowing seeds. I give myself extra work by growing almost all of my early plants in modules. This keeps my plants away from slugs, voles, birds, and the worst of the weather, and allows me to give the optimum tmperature for germination using electric propagators. In fact if I had been sowing seeds outside this Spring I’m not sure how many would have made it. As well as needing a bit more work, sowing seeds in modules, rather than sowing them directly in the ground, creates the need for a suitable growing medium. I had read a book which suggested that mixing dried cow manure and river sand makes a good seed sowing compost, but I don’t have either to hand. In the past I have relied on bought in ‘multi purpose’, sieved and mixed with sand, but with the volume of seedlings that I grow, and the trees and shrubs in pots, this is expensive, not particularly ‘green’, and may in fact be responsible for creating some of the disease problems that seedlings suffer from. This year I have made some changes to the way that I go about sowing seeds.
Healthy Soil and Sowing Seeds
A 5 – 10% level of organic matter in soil is considered good for agricultural purposes, yet many ‘bagged’ composts are almost 100% organic matter, especially the organic/peat free versions. With organic matter holding water like a sponge, using these for sowing seeds means that your seeds will be sitting in waterlogged conditions, which isn’t healthy. Mixing these with sand helps to improve aeration and drainage a little, but this still doesn’t resemble the conditions in which the seedlings will be growing, or should be growing in. Another problem with many bagged composts is that they get wet, and then stay sodden for long periods, potentially encouarging anaerobic microbes, some of which could be harmful to my seedlings. This link describes damping off. I don’t agree with most of the treatment and avoidance measures that they list, but the damp conditions and over fertilisation sound just like the conditions created by wet organic matter.
I have resisted using soil from my vegetable beds, concerned about weed seeds, pests, and disease, but this is not really sensible. A healthy soil should contain everything that a seedling needs. The question has been how best to handle it?
Weeds and Sowing Seeds in Modules
I have been concerned about using garden soil as a growing medium for sowing seeds as I felt that it may lead to me introducing pernicious weeds into the vegetable growing areas, but if the soil is coming from those areas initially, I will only be moving weeds that I already have, and none of those have been a significant problem so far. In practise, as long as when you are sowing seeds you know what the seedlings will look like, anything else is unwanted, and can be plucked out, or cut with scissors. It’s particulary easy for seedlings like tomatoes and brassicas, which are easy to identify. Sowing seeds in little clusters is another way to help with the identification of weeds. Once you can see what the seeds that you have sown look like, anything else can be removed.
My New Seed Sowing Medium
I could have taken some of the soil from my growing spaces to use in my new medium for sowing seeds, but a more simple solution presented itself. I have been collecting the soil that our moles throw up. This has been used as a component in the mix that I make for growing trees and shrubs in pots. I decided that I would use it as the bulk component in my mix for sowing seeds. The soil comes from the top 12 inches under permanent grass. This means that it already has a pretty good organic matter content, and probably a good mix of microbes, good and bad. As we are on a clay subsoil, using this on it’s own leads to the clay fraction filling the pore spaces when it is watered in pots or modules. To keep them open I use sand, some of my own thermal compost, some worm compost, a small amount of Rockdust, and some ‘bagged’ compost.
Making the Seed Sowing Mixture
I use two riddles to separate the different sized particles. The largest has mesh that is about 6mm. The mole hill soil is riddled with this size. Anything that doesn’t pass through the sieve is put to one side and used as the bottom layer in pots and modules, or in larger pots. I do the same with my own compost, vermicompost, and bagged compost. I add sharp sand to these smaller particles. I am aiming for about 75% soil, and 5% each of the others. This isn’t precise. This mixture provides the bulk of my compost for sowing seeds. When mixed I take some of this mixture and pass it through a smaller mesh riddle. This is about 3mm. This will be used to cover the seeds once they have been sown. I use the same sized riddle to add rockdust to the fine mix. Anything that doesn’t pass through the riddle goes back into the bulk mix for sowing seeds. I have used charcoal for to add to seed sowing mixes, but haven’t riddled mine yet and it still has too much wood ash in it. The wood ash will add minerals, but is very alkaline, and too much would not be good for seedlings.
I would like to replace all of the sand with rockdust, but it costs 4 times as much. I use it in the top layer only, for it’s mineral content. I stick to the sand for most of the mixture, for it’s improved drainage and aeration.
Other Soil Amendments
I have some bonemeal, and fish, blood, and bonemeal that I can add to the mixture. However I think that the seedlings don’t need too many amendments. I tend to use these for plants that are going to spend prolonged periods in pots. My preference would be to replace the bonemeal with rock phospahate, but this is also expensive to buy in smallish quantities. My early trials with compost tea showed that it gave an initial boost to seedling growth.
Beneficial Microbes and Compost Tea
Whilst a healthy soil should contain plenty of beneficial microbes, I use compost tea to water the modules initially. I also use a highly diluted compost tea to water the seedlings. When the weather is cold, it’s difficult to multiply (brew) microbes in a compost tea brew. So I mix vermicompost, liquid seaweed, and molasses together, and water with it. Sowing seeds into modules that have been watered with this mix, and which are then put into a warm propagator, should create the same conditions. I think that this is important. Plants secrete sugars from their roots, which then feed microbes. These multiply, and are eaten by nematodes and protozoa, releasing nutrients that the plants can use. By adding simple sugars (molasses), minerals (seaweed), and beneficial microbes (vermicompost) I aim to start that process early. By the time that the seedlings are producing a surplus of sugars, there should already be a healthy population of microbes present.
If I have any commercially produced fungi to use, I do sprinkle some around the seeds, but I tend to save this for the more important plants. Although Vermicompost tends to be bacterially dominant, if the worms are fed with more woody material, the fungal component can be higher.
Sowing seeds using my latest seed sowing mixture have been good so far. I hope that this will improve when I start to add more crushed charcoal to the mix. The real test comes when the seedlings start to get crowded and stressed. This is when damping off is most likely to occur. I always hope that having a healthy population of microbes will help, but have little way of confirming that without side by side testing.
I hope that this post has been useful, interesting, or thought provoking. Let me know what you think