If you are thinking about stocking up on compost for this year’s containers, it’s worth taking a moment to consider what you really need.
All-purpose compost tends to be pretty fibrous and is formulated to hold plenty of water. That’s fine if you are growing thirsty plants or you struggle to keep up with watering. But what about plants that like to be on the dry side? What should you be potting succulents, pelargoniums and aeoniums in?
A less spongy, loam-based, John Innes-type compost will suit them far better that the all-purpose kind. (Apologies, it tends to come in dense, heavy sacks rather than the big loose ones.)
One of the reasons people moved from loam-based to peat-based composts decades ago, then to ones that are coir and wood fibre-based, is that even loam can gradually become compacted in a pot, settling in the base until the drainage holes clog and the compost becomes soggy. That’s hardly what you’d want for drought-loving succulents.
This is why you should get yourself a bag of horticultural grit to mix with your compost, to open it up and keep it free-draining. For succulents I regularly mix up a compost that is two-thirds grit — it’s a lot I know, but they’re happy in it, and in a compost that is so free-draining they don’t give a damn about Monmouthshire rainfall. It also means that, when they come under cover frost-free and virtually unwatered in winter, the drainage is perfect and even lifesaving.
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Of course, in adding all that grit you are diluting your compost — there is far less nutrition there for the plants, so you may want to top it up with a bit of liquid feed over the summer. Better this than a plant that rots off at the root in spongy compost.
In truth I sometimes add a bit of all-purpose compost as well — just for sheer bulk — if I am potting uncomplaining plants such as pelargoniums, which hate wet roots but don’t have to be especially dry. There’s no magic recipe and I wouldn’t stop you playing about with your own. I suppose mine is something like 40 per cent loam-based, 40 per cent all-purpose compost and 20 per cent grit.
Using an unglazed clay pot rather than plastic is always good for drought lovers because moisture evaporates away through the clay. However, whatever the pot’s material, no plant — whether it’s a drought or a damp lover — likes sitting in a potful of unused compost. And for drought lovers it’s a really good idea to put broken or even whole bricks into the bottom half of the pot, nestled and bedded into the compost, like aggregate in concrete, so that they are almost part of the mixture. Then they will absorb water, as will the compost, yet never sit soggy.
Try unpotting something that has been grown this way and you’ll see how the roots of a geranium have clamped themselves around the brick, or how aeonium roots have glued themselves to the walls of the pot, searching for moisture, but never sitting in excess liquid.
Good drainage is everything and it’s something you can get right at the start when you are potting.
