
Photo: Bill Kerr
There are various commercial seedling growing mediums available on the market. These are generally safe to use, but with seedling production you need to keep costs as low as possible while still producing good-quality seedlings.
Imported components are costly, but poor performance is costlier. There has to be a balance between quality and cost.
I once did a big trial for a seedling producer who was using a commercial pine bark medium and fertilising through his irrigation system. I took 25ℓ plastic containers and made different combinations for each one.
I would use the pine bark medium and mix in various combinations of agricultural lime, potassium sulphate, trace mineral mixtures, urea formaldehyde (slow-release nitrogen), and superphosphate.
I used one-third sifted cattle manure on half of the mixes. The seeds planted were tomatoes, peppers, lettuce, Swiss chard, and cabbage. One tray was used for each mixture.
The results were very revealing. What was particularly significant was that all the trays containing cattle manure produced seedlings with substantially stronger root systems, which allowed even smaller lettuce plants to be pulled.
All the trays with added trace nutrient mixtures did not show any benefit from it. Also of interest was that some mixtures produced better pepper seedlings and others better tomatoes, and so on.
Successful mixture
One mixture resulted in seedlings of all species coming out very well. This mixture consisted of one-third sifted cattle manure and, to every 1m3 of the mixture, I added 500g lime, 1kg superphosphate, 500g urea formaldehyde, and 200g potassium sulphate. With this mixture, the medium didn’t need any further fertilisation after seeding.
This recipe may not work for everyone, but is an example of one that seedling growers can follow for an economical mixture that incorporates local resources.
Using horse manure
Producers who live near a race course or stables can consider using horse manure compost as a growing medium. I have been doing so for a number of years.
Horse people consider the manure a waste product and are only too happy for someone to take it off their hands. Most use wood shavings as bedding material in the stables, and when there is too much manure and urine in this bedding, it is removed and replaced.
When this waste is stacked, the temperature can reach about 70°C within 24 hours. When it cools down, it is turned.
You should move the material that was on the top and at the sides into the middle of the turned heap so that it will start to decompose, heat up, and destroy any weed seeds.
Often, teff fed to the horses in the stables will release seeds that need to be killed off.
Once the pile has cooled down after the turning, it pays to introduce some Eisenia arnoldii (red wriggler) earthworms, which will add to the quality of the compost. When the compost is properly broken down, it makes a wonderful seedling mix that doesn’t need fertilisation and is ready to use. The texture is such that damping off is unlikely.
Bill Kerr is a vegetable specialist and breeder.