What was the context, Amsterdam? Are you sure he didn't say "weak compost tea"?

Without seeing the programme, I would say that he might be referring to a seed and cutting compost which would have very low NPK.

If you use regular compost, can't you just apply half the recommended application, or less?

Monty had split a plant & was potting up the plantlets, he did say use weak compost as he didn't want a lot of soft new growth.

I use the cheap and cheerful compost for this. I've just split large pots of primrose and Geranium Samobor using it.

As far as I could tell, Ol' Monty meant a compost lower nutrients, such as a John Innes seed and cutting compost. I also noticed he had added either sharp sand or fine grit to further increase the inert mineral content.

The point he made was that multipurpose would be too rich in nitrogen and the foliage would grow lush without commensurate root development.

That's what I thought Buddlejagarden. Thanks for clearing that up. Will get some seed compost as I have got some dividing to do.

Learn something new every day. Here in the States, practically all "composts" have low NPK levels, just enough to keep them from stealing nitrogen from the soil when used as a soil conditioner. The only exceptions are home made composts with plenty of veggie scraps, and a few commercial brands that have had timed release fertilizer added to them--and usually have other problems, especially used as potting compost. Also, potting composts are sold as "potting soil"--even though actual soil is not involved--or "potting mix".

Tugbrethil - I've also seen it label "Seed Starter Mix." Don't ask me what's actually in it. It could just be a marketing machination to sell more dirt. :)

I've just joined the group after googling 'weak compost' as I too saw Monty last night and wanted to know what to use!

Seed starter mixes that I have sold in the past are pretty consistently peat moss and perlite, in varying proportions. Some are advertised as being pasteurized, to eliminate disease organisms, but those are also, as usual, sold in perforated bags. :/

Thank you! I just signed up as I'm catching up on GW and wondered what weak compost is.

Tugbrethil - the confusion is to do with terminology differences in the UK and the States. Here 'compost' is a term used for both soil conditioning materials AND potting soils; technically, the latter are called 'potting composts' and may be multi purpose, John Innes 1, 2 or 3, or John Innes and multipurpose mixed together, or ericaceous potting compost. Soil conditioning ones are just called compost (garden compost, composted manure and the like).

It would be much clearer if we talked about potting soils rather than potting compost, because mostly, we Brits will say we're off to get some compost from the garden centre, or some multi purpose, which does not make it clear precisely which 'compost' we're speaking of. I have always had to give explicit instructions, usually with a photo, of a soil conditioning compost to buy to a client, or they'll come back with potting compost... it can be a real pain, this word compost, when not allied with an adjective!

And yes, I agree that Monty would have meant John Innes No 1 or seed and cutting compost, which have a pretty low nutrient (especially nitrogen) content.

My customers have brought back many a dead plant potted up in soil conditioner labeled "planting mix" at the DIY store! :] The manufacturers think that it is good marketing, but it is just confusing.

Thanks everyone for clearing that up!