Monday, 23 July 2012

Pot compost - breaking the rules


I used to ridicule gardeners who used soil in pots. Now I do it too, almost all the time. There are very good reasons NOT to use garden soil – it is full of weed seed, weed root, pests and disease. Worse, soil in a container does not behave like it does in the ground. It will usually hold too much water in proportion to air.  It will have insufficient nutrients and clay soils will crack when dry.

Pots in the courtyard
 My Seaton Ross soil is unusual and is almost pure sand. Sandy soils are not usually water retentive. Mine, because the sand has very fine grain, is both water retentive and aerated. This is indeed a stroke of luck. Very few gardeners share such a suitable soil. So the bad news is, I really cannot recommend use of soil in seed trays and small pots without a lot of provisos!

Now the good news!  What if you want to fill large tubs and planters? Your soil might just be suitable, especially if it naturally contains plenty of organic matter. You will have to mix in fertilizer and, perhaps, lime. I add dolomitic limestone and a ‘coated’ slow release fertilizer such as osmocote. Limestone or chalk are alternative forms of lime. The hydrated lime sold at garden centres is probably too soluble.

Mixing my soil compost is another reason for the no dig gardener to use his beloved spade!

These pots are the right  sort of depth to be suitable
for a soil compost
Many gardeners do not realise that growers’ suppliers will usually also sell to amateur gardeners (although they will not usually sell professional pesticides). It is necessary to buy in larger quantities and to know what you want. My dolomitic limestone (called dolodust) comes in a 25kg bag from our local East Riding Horticulture at Newton on Derwent.

And finally…
My ears are burning - I can hear you saying ‘no wonder he is a no dig gardener, he’s on sand’! The truth is that clay soils benefit much more from no-dig than do sandy soils, which bring their own special problems.


5 comments:

  1. Nigel, Newton Aycliffe23 July 2012 at 13:32

    Sad to say I lost most of my decent big pots to frost in that cold spell last January. Only the shallow ones survived! Reading this is my excuse to go out and invest in some new ones!

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  2. I got 2kg of Osmacote on Ebay for only £3 - it's the cheapest I've found anywhere so far.

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  3. I have always grown quite a lot of herbs and vegetables in big pots, using a mixture of garden soil and compost. The main reason being economical! Seems to work for me. I find that lining the pots with old papers stops them drying out so fast too.

    I love the fish Roger!

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  4. and I am sure you have realised by clicking in the tank you give them some food.

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    Replies
    1. Certainly not bored, but a nice diversion!

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