Considering Professional Compost instead of Garden Centre Brands

I have always used John Arthus Bowers (JAB) Multi Purpose - it is relatively cheap, I buy it from local garden centre (when on special offer), I buy in the Autumn because I find it is much easier to use (spring-bought often waterlogged etc.). It contains some rubbish, but doesn't seem too bad - I sieve it anyway, just to find the compacted bits so I can break them up in order to have a nice consistent material to work with when I prick-out / pot-on. I use a 1/2" sieve for potting on (plants won't mind some small lumps) and 3/8th" for pricking out into modules (so that there are no lumps in the small cells).

I mix with 10% Perlite (2-5mm grade, rougher than that [which is what is generally available, particularly for hydroponics] doesn't do the job IME, or needs a lot more used which is then a higher cost) by volume.

I add a measure of slow release fertiliser ("hundreds-and-thousands") when I pot on, and occasionally feed with, say, Miracle Gro as well.

I've been disappointed with the growth of plants this year. Can't quite put my finger on why, but when potting on the root development in many of the plants has not been as good as I would expect, and the compost has been noticeable bitty - i.e. things that look like little bits of sticks and so on. They were there are the outset of course, and the Perlite keeps the compost open - which I consider to be key - but it somehow doesn't look "right" to me. The additional of Perlite definitely keeps the compost "open" - in fact potting on is now more tricky because if the rootball is not fully developed it tends to fall to bits, whereas in the old days compaction would have meant that it was pretty much rock hard after the 6-8 weeks the plant had been in the smaller pot. I think the plants are much happier with the open compost.

I've though for some time that I ought to try a professional compost. I needed to pot on some Acers recently and treated myself to a couple of large bags of Levington Ericaeous compost - not used Levington for ages, but it figured in my brain as a quality brand. However, it was very disappointing, lots of fibrous stuff in the bag, but also lumps, stones [not pebbles - stones that were more than 1" across], twigs and all sorts - I had expected a consistent, fine, material. So that was a negative ...

I buy [other] materials from a horticultural trade supplier from time to time - particularly when I need to buy in bulk, so as to get a good price. So I decided to buy some of their Sinclair specialist composts. It turned out not to be an easy thing to do!!

First there is the price discount. To get anywhere near Garden Centre prices then it is necessary to buy in fairly serious bulk - that has put me off for a while, but I would not be adverse to buying a whole year's requirement in one go.

But that leads me to problem #2 which is that the range they have to huge, and I have no idea what the difference is, and I didn't want to buy a lot of bags with trying a sample ... but single-bag price is very expensive. The range includes:

• Professional Propagation Compost
• All Purpose Compost
• Tree and Shrub Planting Compost
• Nursery Stock Compost
• Container Compost

which all looked promising for one job or another

plus:

• Fine Grade Pine Bark
• Nursery Grade Pine Bark
• Modular Seed Compost
• Bulb Compost
• Primula and Pansy Compost

They come in 75L bags (and are significantly heavier than the 65L bags of JAB - so "denser" in some way), and a single bag is 14.8p/L . Buy 90 bags (6,750L !!) and price falls to 6.3p/L

JAB costs me around 4.6p/L when it is on offer ... so even if I buy nearly 7 tonnes of Sinclair it will still be 50% more expensive.

However, I mix in 10% Perlite with the JAB so that increases the price a bit, and I sieve out probably 5%-10% of lumps too (although they get used up in large-container planting), so that maybe narrows the price gap a bit.

So for the record I bought:

All Purpose Compost (several bags as I figure I should be able to use this for pricking out and 9cm potting-up)
Container Compost (A few bags to try it out on larger potting-on items)
Nursery Stock Compost (1 bag to see what I think)
Nursery Grade Pine Bark (1 bag as a test - I do incorporate some bark into some things when I pot on - when the plant needs a really open, free draining, but water retentive structure)

The All Purpose is nice and fine and very consistent. There are lumps, but they are just compression lumps (although I think I will have to sieve it to find them and break them up before using it). I doubt I will need Perlite add-in, but I might try an experiment.

The Container Compost is quite rough, but I think will be good for longer term potting on / bigger plants & pots. Its cheaper for a bag, but more expensive in bulk [compared to All Purpose].

Haven't opened the other bags yet.

For my first experiment I have potted on a number of different plants (which were in 9cm JAB+Perlite) into 1L with either JAB+Perlite or the new All Purpose . All have also had a measure of Osmocote slow release fertiliser added, and I'll compare how they do. They are only going to be in the 1L pots for a couple of weeks before being planted out (just want to get a bit more greenhouse-boost to hurry them up ahead of planting out), so it may not be an ideal test.

I wonder if the fertiliser contents of the Sinclair Pro is way higher than the JAB, and that I didn't need to add slow release too? If so that might level the price playing field.

Product descriptions:

All Purpose
Peat: 0-5mm 15%, 0-10mm 80% Sand: 5% pH: 6.0
N 192 P2 O5 224 K2O 384 g/m3
Easily managed general purpose peats and growing medium. For all year round propagating and raising of salad, vegetable, bedding and pot plants in pots, trays and packs.

Container Compost
Less coarse than Nursery Stock and without grit. for both ericaceous and non-ericaceous species.
Peat: 0-10mm 50% 3-15mm 25% 15-25mm 25% pH 5.0
N 120: P2O5 140: K2O 240 g/m3

Nursery Stock
An easily managed coarse grade growing medium with bark & grit. Recommended for both ericaceous and non-ericaceous species.
Peat: 0-10mm 25% 3-15mm 27.5% 15-25mm 27.5% pH 5.0
Bark: 8-16mm 15%
Grit: 5%
N 120: P2O5 140: K2O 240 g/m3

Not exactly Peat-Free as you will have noticed ...