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How can something aid drainage and retain water? (e.g. perlite)
Matty_P
Posts: 64
Hi all,
Are these not opposites? Either you want something to drain i.e. water passes through quickly or it retains the water. How can perlite do both?
Most gardeners I see on TV, mention no names, seem obsessed with drainage. Granted it is important but if the majority of plants need good drainage I'm surprised at how frequently it's mentioned. Why doesn't it go without saying.
Thanks for the comments.
Are these not opposites? Either you want something to drain i.e. water passes through quickly or it retains the water. How can perlite do both?
Most gardeners I see on TV, mention no names, seem obsessed with drainage. Granted it is important but if the majority of plants need good drainage I'm surprised at how frequently it's mentioned. Why doesn't it go without saying.
Thanks for the comments.
1
Posts
Yes they will seem obsessed with drainage as some plants just perform so poorly without good drainge. Bearded iris (one of my favourites) need excellent drainage to perform really well. It doesn't go without saying as there is a continuum; some need excellent drainage, some it doesn't matter too much and some need poor drainge. I just planted some camassia bulbs in a really waterlogged part of my garden and they love the fact it doesn't drain well. To illustrate further, one episode when Monty was working on a damp garden planting scheme he put a plastic membrane down to ensure it didn't drain well.
To show this, imagine you dig a hole for a new plant in very heavy clay soil. Once the whole is dug if you chuck a bucket of water into the bottom it can take ages to drain away and will just sit there as a puddle at the bottom. If you added a thick layer or perlite at the bottom and repeated what wouldnn happen? It would definitely get wet as it absorbs water but it will drain away almost instantly. By the way this isn't an example of how to use perlite but to show you how it can both become wet and give great drainage. Perlite is great for mixing into pots to improve both drainage and water retention.
Surely if we gardeners continue to plant our so many plants that require good drainage, the much of the water we work hard to collect, just sinks below the beloved plants - and is effectively wasted.
Are we gardeners therefore guilty of deliberately wasting that precious resource?
My last garden, which was in Dordogne in a limestone area, like the Cotswolds, was very well drained. I had to dig in masses of compost to retain water, so it never occurred to me to use grit when doing cuttings. They were fine without grit. Anyway the local French GC didn't sell perlite or grit. Also I never stood pots on pot feet and they got too dry. In summer I used pot saucers to help keep the soil moist.
An open mix is the ideal, and that's what it provides, while the remaining soil/compost can hold enough water for thoses tiny seeds/plants.
You wouldn't use it for anything much bigger, or for open ground though. Utterly pointless. Even grit is fairly pointless in very wet soil, but a better choice for pots/containers when it's for plants that won't appreciate being too wet. In consistently wet soil, that's when organic matter is needed.
I'm not sure I understand your query @rowlandscastle444. Unless a plant completely dried out, the water filters through and would be available to the root system. Any excess would eventuallly drain away. Having adequate drainage just means the plant isn't likely to get waterlogged, but will be able to take up what it needs. It's only wasted if people plant in unsuitable soil conditions for the plants they have, and then add too much for it to be useful to those plants.
Potted plants are different of course, and have to be treated to suit them - a saucer, as @Busy-Lizzie describes, is ideal for many in drier areas to prevent rapid moisture loss.
I live in west central Scotland - not where that photo is...
It is weird stuff. How I have heard it described is like pop corned volcanic rock.
Because it is expanded material it has little air pockets which can hold water but also allow any soil it is added to, to drain away the excess. And leaves air gaps.
Sorry I am not sure if I am even right, or explaining it well.
I have only just started using it experimentally for plants that need good drainage in troughs and pots as an alternative to grit, which can be heavy if you need to move said pots and troughs.
So far everything has survived that I have used it for, but not convinced some things prefer a "heavier" mix .
And the darned stuff floats when you water if it is on the top of the soil, so I am now top dressing with grit on some pots.
I may have put too much in but it makes for very lightweight troughs I can lift.