Perfect mix for potting power
HUMANS have been using pots to transport plants from camp to camp since prehistoric times. We have come a long way since then, and so have the plants the pots and the mixes in which they grow.
Many gardeners of my grandfather’s and even my father’s generation dug soil out of the garden to use in pots.
This can be a problem as soil does not behave the same way in pots as it does in the ground. Sandy soil will drain too well and then become hydrophobic and clay soils can stay too wet and will set like concrete.
There are a few qualities that a good potting mix should have, one is that it should drain well and the other is that it should have good water capacity.
This last statement may sound like a contradiction in terms but there are a few different classes of water.
The mix should be able to hold onto water in its pores – this is called capillary water – but excessive water should be free to drain away, this is referred to as gravitational water.
A good mix should hold and release nutrients well and it should have a neutral and stable Ph.
In normal garden soil, neutral Ph is about seven, this is when all the nutrients are unlocked and accessible to plants, but in potting mixes which are comprised of a lot of organic matter, neutral is about 5.5 to 6.
You may have come across the term “air fi eld porosity” in relation to mixes, this just means how light and fl uffy the mix is.
This is especially important in relation to seed raising mixes because airy mixes mean good root development.
Most mixes should have a fairly regular particle size and they need to be dense enough to provide the plant with good support so it does not just fall over.
You can either start from scratch and make your own potting mix or you can adapt an existing mix to your own needs.
There are several ingredients you can play around with that will form the main part of your mix:
Coir fi bre: Has good water and nutrient holding capacity.
Coarse washed river sand: Is dense and adds structure to the mix and also provides good drainage.
Composted bark: Good nutrient and water holding capacity.
Mushroom compost: Provides good stability, water and nutrient holding capacity.
Vermiculite: Good water and nutrient holding capacity.
Perlite: Good to lighten the mix, it can be advisable to wet it down before use as it can be dusty.
Fertiliser: This can be blended through the mix or added to the pot after. Remember, what fertilisers you use will depend on what plants you are growing. Personally I prefer a complete organic fertiliser as this feeds the potting mix as well as the plant.
Seed raising mix: Equal parts perlite and coir fi bre. I mulch the top of the pot or tray with a thin layer of vermiculite to protect the young seedlings and keep them moist.
Cutting mix: Equal parts course sand and coir fi bre.
Basic mix: One part course sand, one part composted bark and one part mushroom compost.
There are many potting mixes available on the market and making your own will not necessarily be any cheaper but you are able to tailor the mixes to the needs of the plants you are growing and it is also loads of fun. It is the gardening version of baking a cake.