Saturday, 15 January 2011

Riding one of my hobby horses AND SHOUTING A LOT.


Every year I am surprised by how the plantings stand up to the weather. This winter they have been frozen, covered in snow for weeks and now they are being steadily rained on.  Now I have cleared the dead foliage away from the displays I can see that very few plants (except for a few I knew were not exactly hardy) have given up the ghost so far. The answer is good drainage.

Plantings outside the Octagon this week

Hello? Hello? Can you hear me?
Do you ever get that thing when you say something in a group conversation and no-one seems to hear you, then a couple of minutes later someone says exactly the same thing and everyone says "Oh yes, good point, how clever!"? Is it just me? For about ten years I have been telling everyone who'll listen that you don't need to put a thick layer of crocks at the bottom of the pot you are planting. I have been tempted to stop people in garden centres and lecture them. Perhaps I should get a sandwich board and walk up and down Main Avenue at Chelsea: "DON'T BOTHER WITH A LAYER OF CROCKS, IT DOESN'T IMPROVE DRAINAGE AND WHEN YOU REPOT IT WRECKS THE ROOTS OF YOUR PLANTS AND MAKES AN ALMIGHTY MESS! By the way, the end of the world is nigh."

Well last weekend The Guardian printed an article, "Slugs, Snails and Old Wives' Tales", first printed in Gardening Which? One of the revelations was that a layer of crocks not only "reduces the volume of soil available to plant roots", but "research by soil scientists shows that water doesn't flow freely from fine-textured materials into coarser ones." Hooray! I told you so! A layer of crocks is not just useless but positively harmful, having no beneficial effect on drainage it creates air spaces which impede drainage and root growth, provides a cosy home for slugs, and falls out at re-potting time, ripping fragile roots.

So ignore all those pesky old wives.
What you do need to do is 1) select a pot that has a decent drainage hole or holes (Whichford ones all do) so that when water percolates down it can get out easily. 2) Cover that hole with a crock or two or a piece of polystyrene to stop the compost from falling out. 3)Use a decent compost with plenty of grit that doesn't have a sticky, claggy texture. 4) Be assured that Bob is your avuncular relative.

It seems that much horticultural advice in the printed and broadcast media is merely people repeating things they have heard but never actually tested or observed for themselves.  In my opinion Gardening Which? magazine is the best at taking nothing as read - they routinely test methods, plants and equipment.

And another thing...
The other issue that gets my goat is pot feet. Magazines, books and television programmes all assure you that it is necessary to raise your pots on pot feet during the winter. WRONG! If you use a good terracotta pot (preferably from Whichford...) and place it on the ground - concrete, gravel, or bricks but preferably not soggy grass - the water will seep nicely through the small gaps between the slightly rough terracotta and the slightly uneven ground. Think of your bath sponge: when you dunk it and raise it in the air it drips a little, but as soon as it makes contact with your hand the water pours out. I'm no scientist but I think it has something to do with capillary action, the water moving more easily through a small gap than through thin air. All you have to do is make sure that the gaps under your pot don't get sealed by algae - just shift the pot a little occasionally.

I have to admit that we do make and sell pot feet because people ask for them. Of course ours are decorative and they can keep your plantings out of puddles, on the other hand they can make your pot wobbly and easier to knock over, they provide a lovely roosting space for snails and they let the frost in to the base of the pot so that the whole thing can freeze solid much more quickly. You will often see pots in displays here raised on brick plinths, this is not for drainage reasons but simply to raise the pots so that a bigger display can be installed in a smaller space; the base of each pot has good contact with a layer of bricks and large gaps are kept to a minimum.

My friend shouting on Thursday morning

Right, I will now dismount and go back to enjoying the robin's song and hoping that we have more of the mild weather. Feel free to share any of your own horticultural hobby horses with us - oh and if any physicists can give me a digestible explanation of why tall, thin pots drain better than short, wide ones I will be very grateful...

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