[cathangirl]

Is it possible to prepare good, home-made seed compost?  Or is bought seed compost the better option?  Last year, I sifted loads of compost to a very fine end result, but not much luck with seed germiation.  Does that answer my own question?   

Many thanks in advance.
cathangirl

[peapod]

Your home made compost will be too full of nutrients to grow your seeds well

Some people do make their own, Im sure they will come along and give you a recipe or two soon 

[savbo]

this year i've mixed 40% coir, 40% sieved B&Q MP peat-free and 20% vermiculite and it feels good and seems to have a nice feel and good water retention... but still waiting for toms to appear!

M

[peapod]

 Did it work last year Savbo? Or did you use something else?

[BostonInbred]

Seed compost has to be low in nutrients or the ionic activity of the mobile minerals literally fries the roots and root hair on small delicate seedlinsg - its a bit like dipping them in battery acid.

So you need a fine substrate low in nutrients.

If your going to buy, the best option is a John Innes Seed Compost, which is loam based. If you want to try making your own, heres the recipe

John Innes seed compost: In the following loam is sterilized and peat and loam are passed through 9mm sieve.

# 2 loam, 1 peat, 1 sand
plus

# 0.6kg ground limestone and
# 1.2kg superphosphate per 1 cubic metre of mix.

[BostonInbred]

Since this subject has arisen several times. heres an explanation regarding WHY too many nutrients in a compost kill seedlings.

Take the case of nitrogen. The process by which plants take up nitrogen is called Nitrogen Fixation.

Plants that contribute to nitrogen fixation include the legume family – Fabaceae – with taxa such as clover, soybeans, alfalfa, lupines and peanuts. They contain symbiotic bacteria called Rhizobia within nodules in their root systems, producing nitrogen compounds that help the plant to grow and compete with other plants. When the plant dies, the fixed nitrogen is released, making it available to other plants and this helps to fertilize the soil

The initial chemical process goes N2 + 6 H+ + 6 e− → 2 NH3

i.e. 2 nitrogen atoms plus six positively charged Hydrogen ions plus  6 electrons give 2 molecules of ammonium radical.

The electrons come from the plant - in effect a electric current flows between the plant and the surrounding soil/compost, in exactly the same way an electric current flows between the plates of a lead acid battery. This is why the basic test of the nutrient levels in a compost is the electrical conductivity. And like any other electrical circuit, its possible to cause a current flow so high it 'melts' the wiring or blows the fuse, ie destroys the fixing bacteria on the root nodules. This is what happens when the nutrient levels are so high the electron flow becomes too energetic and destructive. Once the nitrogen fixation system has been destroyed by the current flow, the plant is doomed.

[solway cropper]

Boston, have you ever measured the far end of a faarrrt? 

[johnfh]

Boston

Good to see a serious attempt to recognise and explain the science of gardening on this generally excellent and friendly site.  Keep it up!

[cathangirl]

Many thanks for all your serious replies.  Methinks I'll be buying some seed compost tomorrow!
cathangirl

[Kristen]

I agree with the John Innes soil based Seed Compost. I've had much better results with that than,say, Levington peat-based "seed compost".

Had to sieve it first as its usually full of rocks etc I reuse mine over and over during the season. I realise that this is not good advice, as soil borne bugs will perpetuate, but I just re-sow the little 1/4-sized seed trays. I do leave them for a couple of weeks on the windowsill propagator with their clear plastic lids on to encourage any slow-germinators from the previous crop to make an appearance! otherwise my next-crop has some volunteers from the previous one

[scabs]

I never realised compost was so interesting.

[savbo]

Did it work last year Savbo? Or did you use something else?

have used the coir and B&Q peat-free before, worked OK and fewer sciarid flies than B&Q alone. My logic was that the coir is v low on nutrients so some MP compost would add some nutrients but not too much. This year's innovation is the sieving and the vermiculite - cos I had half a bag sitting around!

[BostonInbred]

Did it work last year Savbo? Or did you use something else?

have used the coir and B&Q peat-free before, worked OK and fewer sciarid flies than B&Q alone. My logic was that the coir is v low on nutrients so some MP compost would add some nutrients but not too much. This year's innovation is the sieving and the vermiculite - cos I had half a bag sitting around!

Correct, coir has zero nutrients, its a bulker to reduce the amount of peat.

[savbo]

should have mentioned in ealier post - first batch of very happy looking tom seeds have popped up yesterday - though as toms aren't that fussy that's not a great test of the compost mix. will post again on how peppers, okra, aubergine, lettuce and celeriac do!

M

[peapod]

should have mentioned in ealier post - first batch of very happy looking tom seeds have popped up yesterday - though as toms aren't that fussy that's not a great test of the compost mix. will post again on how peppers, okra, aubergine, lettuce and celeriac do!

M

keep us posted