Want to sow seeds in pots? What do you need? Seed raising mix? Guess again!
Working part-time in the garden nursery industry, I meet many gardeners who have had problems sowing seeds in seed raising mix – they find that their seeds sprout but their seedlings only reach a very small size and then completely STOP GROWING, and the resultant seedlings are very thin and spindly!
That’s because seed raising mix has absolutely no nutrients in it, and is totally unsuitable for growing seeds in. It’s actually misnamed, it really should be called SEED COVERING MIX or SEED GERMINATION MIX, because that’s what it’s designed for, and does well.
What is Seed Raising Mix?
Typical seed raising mix contains Composted Bark, Crushed Quartz, Trace Elements and Wetting Agent.
The composted pine bark in seed raising mix is of a fine consistency, allowing seedlings to push through easily to come to the surface, and to push their roots down also, without any obstruction from chunky pieces of composted bark you find in regular potting mix which would get in the way.
Composted pine bark is the main ingredient in all potting mixes, and is the component in the mix which holds water. The crushed quartz improves drainage, preventing rotting of seeds and fungal diseases in seedlings. Together these two ingredients achieve ideal moisture retention.
Seed raising mix works well for rapid germination of seeds and encourages strong root development, and that it does well, but it can’t grow plants!
Using Seed Raising Mix Correctly
For seedlings to grow to the point where they are large enough to transplant, you need a nutrient-rich mix, which seed raising mix is not.
So, how do we raise seedlings using seed raising mix?
- Fill the seedling tray with a quality potting mix (which will contain nutrients) that has been sifted to take the coarsest particles out, or use a fairly fine grade potting mix.
- Place seed on soil surface and gently press so seed is level with the surface.
- Cover with a layer of seed raising mix equal to the height of the seed.
If you want to use straight seed raising mix (because you bought a huge bag of it), mix it with a nutrient source such as worm castings or a very small amount of well composted cow manure, or both. If your seedlings germinate AND grow, you know you’ve got the right blend!
Thanks for this. I bought commercial seed raising mix, but the problem I’m having is keeping it moist, without it being saturated. I find the longer I keep the seedlings in small containers, the less the grow and more likely they (get a fungal disease?) and start to die off. Basically, the best success I have is to put them into the ground after germinating with a cloche to protect them from pests, but it seems like a lot of effort for minimal gain…I’m definitely doing something wrong.
When the seedlings have put out their first true leaves, it’s time to transplant them into a growing medium that will give them the nutrients they require. You can transplant them into a pot. See my article Starting Annual Vegetable Seedlings Indoors for more information on this technique.
I think that some of these products worked better before they were so ‘improved’. (Of course, back then, more seedlings were damping off.)
I like using seed raising mix and then transplanting into potting mix. I find that if I put potting mix below the seed mix then I create a potential damping off problem because I get rapid growth of seedlings too close together. If the plant stops growing or yellow/purples off then that is a signal that it is time to transplant into potting mix.