At this time of year I’m putting a lot of plants into pots. This will include sowing seeds, pricking off seedlings, potting up young plants from the propagator, potting on plants into bigger pots and potting up plants that have been dug from the ground.
As an ex nurseryman, I know that professional growers do not generally use the type of composts available in garden centres. When I left the industry around four years ago, most nursery stock was still being grown in moss peat, coming from Ireland, Finland or the Baltic states. To this would be added a controlled release fertilizer and ground magnesian limestone. Fine peats and green waste don’t have the right physical properties in terms of water retention and air filled porosity at field capacity.
The nursery where I worked had been using peat alternatives for its own production for over 20 years. The main supplier in this area is Melcourt, whose composted wood waste product has been developed over many years and is capable of producing results comparable to peat. We bought directly from them and from a compost producer who used their raw materials in their product.
For the last few years they have been retailing their basic compost, Sylvagrow, as a retail product but it is exactly the same as the bulk professional material we were using on the nursery. We added to it a 12-14 month controlled release fertilizer which fed the plant for a growing season and into the spring of the following year, by which time the plant would hopefully have been sold.
My local retail nursery grows the bulk of what it sells and it does so in Sylvagrow. They sell the 50 litre bags of Sylvagrow at £18 for three. That is cheaper than my nearest horticultural sundries wholesale supplier. They charge a little more for the ericaceous version, at around £9 a bag.
Controlled release fertilizer is never an ingredient of retail composts for the simple reason that it has to be mixed in immediately before being used. Once it is mixed, it starts to release fertilizer and if it is not removed, either being taken up by a growing plant or washed out by heavy watering, it can quite quickly build up to phytotoxic levels.
There are other ways of feeding plants but CRF’s ensure that the plant has the right amount of nutrients available to it for the whole season, all from the granules mixed in before potting.
Last year I had plans for this year that have not come to fruition. It seemed like a sensible thing to do to buy a 25kg bag of 8-9month Osmocote. It wasn’t. I could have bought 3kg on eBay for £22.45. Presumably someone is breaking down 25kg bags and reselling it in smaller quantities. You can get various formulations. It has to be kept dry and it has to kept airtight or it can absorb moisture from the air.
So I have my Sylvagrow and I have my Osmocote. I measure 20 litres of compost into a medium sized sack and add Osmocote at between 2.5 and 4 grams per litre, give it a good shake around to mix it thoroughly and use it within a day or two. I have a small electronic balance that weighs to a tenth of a gram. Bought online for a few quid. I can mix one litre of compost if that’s all I need.
I use Sylvagrow compost as is for seed sowing and for growing things in cells, direct sown or pricked off, which covers most of my veg production. If it needs supplementary feeding I use Maxicrop Triple. For just about everything else, from 9cm pots upwards, I use it with CRF added. It works for me.