Why use compost - a thought.

I am sure nearly all of us use bags of compost for the plants we keep in pots. I have just been having a think about this. You need compost that has been sterilised (to kill all stray seeds) for germinating seeds and then potting on the small seedlings.

But I have been using multi purpose compost to pot up all my larger plants as well. I started with 100% compost, and soon learned that you need to add about a third of sharp sand, or perlite to aid drainage. A short while ago I spoke to a leading grower of Diascia, who informed me that he would never use compost in pots - only soil with added perlite or sand. Now, that requirement was probably driven by his Diascia that need sharp drainage. But it set me thinking and as a result I have changer my compost formulae and add half garden soil. The formulae now is three sixths of soil, two sixths of compost and one sixth of sharp sand.

The mixture feels good. It saves money, as you only need to buy half as much compost. Its probably a lot better for the plant as soil is natural and has all manner of nutrients that compost doesn't have. I am sure it drains better than pure compost, which can get exceedingly soggy when when it rains. And the best part of all is that you can use some of the nasty clayey bits of your soil, but when you add the compost and sand you make a really nice mixture, which you return to the garden at a later date when you have finished with your pots.

Any thoughts?

 

It sounds like a great idea, I think I might give it a go. Thanks

 

Peter I think care needs to be taken when using soil because your using it in a closed environment like a pot you need to ensure it is sterilised not from the weed seed problem but from the bacteria /fungus pest problems that can rapidly build up in this confined space.If I could sterilize the quantity of soil that I would need effectively then that is what I would use. At the moment I use 50% multipurpose 40% J I no3 10% vermiculite to this I sometimes add a percentage of processed F Y M at a later potting stage, all of this is put back in the garden between the repotting stages.

 

When we paved our back garden we saved all the earth . I planted up a lot of pots with the earth and i must say they are doing well , but hey what do i know i`m just a beginner :D :D :D

 

Walnut I take your point about bacteria. I have seen it discussed before, but I am not convinced. Perhaps I have just been lucky. I dig up a large number of plants from the garden and put them in pots, tender ones to keep under glass over winter, some like Asters to plant 6 or more months later as they come into flower, and others to move or give away. They all come with a rootball of garden soil, and after a while I realised it was a waste of time filling the rest of the pot with a fine compost mix. So anything that has come out of the garden gets potted up with garden soil and nothing else.

Garden soil does have bacteria and viruses, but I am not sure why a pot should be more susceptable than the border itself. Even a steralised mix won't remain steralised for that long once you leave it out in the open exposed to the elements.

I believe that we buy a lot of compost out of pure laziness/conveniance/habit. In the same way that we buy ready made meals in the supermarket, which are more expensive, less tasty and worse nutritionally that home cooked food - but are conveniant.

 

I occasionally pot up a cutting with rootball attached into a pot of compost, perlite and slow release fert, and I have never had a prob. But I can't mix soil with my compost, I'd have no soil left in the garden. Especially when you think I have already gone through '4000ltrs' of compost since January.

 

In my garden I am convinced there is a leak into another dimension that accounts for the amount of compost I use... I am trying to make as much as I can but I still have to buy in lots.
Fortunately my garden is quite large so there are areas where I can dig up soil, but if your garden is small where would it all come from?
I am mystified by the constant input of compost- hopefully it is the plants using up food. :confused:

 

hi Liz, I think I know why your compost is disappearing may be you have plants that are too greedy for compost. My banana plants take a lot of compost and water I have to constantly feed and water them. like the one in the pic.

 

Years ago I always added sifted garden soil to multipurpose compost sometimes with a bit of sharp sand.
i think it depends on what you are growing, I dont think it affects large fast growing plants, but I wouldn't use it on seedlings. Used to throw in a handfull of bonemeal as well, just for luck, nothing came to much harm.
These days I do as Walnut, I mix JI no3 with multipurpose in varing quantities along with grit or sharp sand, as you say Peter,...... I've got lazy.

 

Bananas do need a lot of water, but you don't have to add compost to your garden all the time, try top soil, then food wise for soil aswell as the plants either manure, chicken pellets or blood fish and bone. I'm clay loam and my jungle is lush every year! I've never put compost on my garden only in pots, then thats multi purpose with JI, or JI no3.

 

This is one of my bajoos last summer, it is now bigger, when its in full bloom in a few months I'l post another pic.

 

By the way I'm 5ft 6" but had 3" heals on in this pic was ready to go out.

 

In the past I have spent some time looking at American forums on soil, and related technical aspects. One of the recommendations there was that you may use compost for shorter periods in pots (up to say 3 years), but that you should not use it for long term pots such as shrubs and small trees. In that case you should use a soil type based compost. The reason, as I explained in another thread, was that compost decomposes with time and gets finer. After about three years it is so fine that it seriously impedes the drainage of the pot. If soil is OK for long term use, I assume it is OK for shorter term use as well.

If you have a very small garden you may have a problem finding enough soil. But with a slightly larger garden there shouldn't be a problem, because eventually it will all be recycled back into the garden. The soil level in my garden is definately rising as over the last 5 years I have bought in several tons of sharp sand and gravel, as well as all sorts of manure, compost, and bark mulch. I also added compost and sand from pots and my own compost, and even newspaper. Nothing gets taken out.

Compostee is that 400 or 4,000 litres. If its the later - you have a serious problem, not least with your bank account. :D

 

Never sterilise anything!

All my mixtures are based on JI recipies but I use peat free compost instead of peat. I don't find it a big deal to weed out the obvious strangers like grass or chickweed from a seed tray or potted plant and I rarely have problems with damping off. Soil and compost contain a lot of bacteria and if they are matured well then a balance forms with the good guys keeping the nasties in check. Worst thing you can have for seedlings is a desert where the first nasty to find its way in has free reign to over-run delicate plants or seedlings.

The following has been shamelessly copied from another site :eek: :D

John Innes Potting Compost
JI #1 Base

7 parts loam
3 parts peat
2 parts sand or grit
Fertilizer: 4 oz / 8 gallons (3 grams / litre)
Lime or chalk: 3/4 oz / 8 gallons ( 0.5 grams / liter)

JI #2 Base: Same as 1 but double the Fertilizer and chalk
JI #3 Base: Same as 1 but triple the Fertilizer and chalk

JI Seed compost:

2 parts sterilized loam
1 part moss peat
1 part sharp sand
The loam and peat is put through in 3/8 in (9mm) sieve.

To each bushel or 8gal(36 L) is added:
1-2 oz (42gm) superphosphate
1/2 oz Potassium nitrate
4-6 oz (21gm) ground limestone


Ericaceous Mix: Use the base but leave out the Lime

Soilless: 3 parts peat and 1 part sand

 

Thats why I use JI no3 for permanent pot planting cos its heavy loam based, then I just feed during the summer and sometimes take the top inch off and re fresh with more no3. As for garden cos I'm clay I've added grit and manure, my soil is good being clay loam with a ph of 6.5. I only add sand to my pots for my agaves and some yuccas and palms.