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What is the magic of seed compost?

GemmaJFGemmaJF Posts: 2,286
in The potting shed
Sorry if this is being covered elsewhere, I would be happy with a redirect to a relevant thread. I've been struggling a bit to navigate the new look forum after a long break from the group.

So I've been doing some head scratching. I want to start making my own seed compost, without buying anything in. Searching the interweb thingy I've found a million recipes recommending some exotic ingredient as the 'essential' element.

So my sticking points.

1) We direct sow seeds into garden soil all the time. They grow just fine, what is wrong with sieved garden soil as seed compost? What can we do to make it better?

2) Is there a simple tried and tested recipe that we can make from ordinary easily available things in the garden? So no peat no coir or other things that would have to be ordered in, are not really considered environmentally friendly etc.

Posts

  • LiriodendronLiriodendron Posts: 8,328
    I suspect the main disadvantage of sieved garden soil is that (in my garden at least) it will be full of weed seeds, competing with your precious sowings.  Plus it may be too rich/acid/alkaline for whatever you're trying to grow, perhaps.  You can sterilise soil by heating it, but that kills the beneficial organisms too...
    Since 2019 I've lived in east Clare, in the west of Ireland.
  • herbaceousherbaceous Posts: 2,318
    I just use old compost sieved from last years greenhouse pots with a bit of my garden compost (sieved) mixed in. As Liriodendron says you do get the odd weed seed but its not too bad usually. Except for the year I missed a dropped tomato in one of the pots  :o
    "The trouble with having an open mind, of course, is that people will insist on coming along and trying to put things in it."  Sir Terry Pratchett
  • Allotment BoyAllotment Boy Posts: 6,774
    Seed compost is also deliberately low in nutrients as high levels can inhibit germination or even damage growth of some seedlings.  If you can get or have any leaf mould  use that sieved fine , it provides an open matrix for roots hold moisture & is relatively low in nutrients. The old gardeners used "loam" from an old turf stack  (turves stacked upside down and left for 2 years) mixed with leaf mould in varying proportions, with added feed for Potting or growing on. It was only when John Innes produced standardised recipes that the use of bagged composts started to come into wider use, now of course they are almost universal. 
    So to answer I would say sieved soil if you know it to be weed free, leafmould if you have any and or some fine grit or sand to keep it "open".
    AB Still learning

  • BobTheGardenerBobTheGardener Posts: 11,385
    Yes, weed seeds and pathogens such as the fungi which cause 'damping off' will be rife in garden soil so not ideal for raising seeds.  In nature, only a few make it because of this which is why many plants produce thousands of seeds; Only a few willl survive.
    You can microwave it in small quantities which will kill off everything as mentioned, but commercial seed compost is pretty sterile anyway.  Plants don't need beneficial organisms until after they have germinated so no problem at all in heating garden soil to use for this.
    I use MPC with additional sharp sand and perlite for germinating seeds but wouldn't hesitate in using sterilised garden soil if I couldn't get MPC.
    A trowel in the hand is worth a thousand lost under a bush.
  • UpNorthUpNorth Posts: 376
    great thread OP.

    i think you would also need to consider which seeds you're talking about.  

    if it's slow going, warm temperature, you're def. going to come across bacteria/mold etc.

    however, take Ricinus and Spanish flag i've just germinated.    about 4 days and 3 days respectively.  so honestly would not have mattered a jot what soil they were in, providing the soil holds moisture.

    but palm seeds for instance...you'd want to be uber careful with your soil.

    personally i buy a small bag once a year, tha'ts enough for maybe 20-30 different seeds i'm doing....and sure it's still a plastic bag, but there's bigger battles when it comes to plastic that need to be won first.  

    and to directly answer....if i was making my own, it would be part sandy soil from garden, part MPC, part water-retaining matter, be that leaf mold or similar from garden, but i tend to use vermiculite with all my seeds.
  • GemmaJFGemmaJF Posts: 2,286
    Thanks all for the replies. Just back in from doing some weeding and plenty for me to go on here. Will have to talk to the parish council about collecting some leaf litter from the local wood. I used to be swamped with it each year from a neighbour's willow, but it was removed a few years back and supplies are now non-existent in the garden.

    I'm not sure about the microwaving, we have one but it wouldn't really be big enough to process a lot of compost. 

    Could soil be sterilized by heaping it over a bonfire or are there other outdoor methods?
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