on the rocks
Does adding a layer of gravel to the bottom of a pot improve the drainage? PHIL DUDMAN has pondered this question and the answer may surprise you
I’ve done this. Lots of gardeners have, and many still do. The advice is often shared freely – when potting a plant, put a generous layer of gravel at the bottom of the pot to improve the drainage.
It makes sense, doesn’t it? Most pot plants hate wet feet, and it’s been proven that gravel has drainage qualities. Turns out, it’s not that simple, and the practice can potentially do more harm than good.
Let’s look at what happens when you water a pot plant. After the excess water drains out, a layer of mix at the bottom of the pot remains saturated for a while, like a suspended water table. This is due to the plant’s capillary action exerting an upward pull on the water.
When there’s gravel at the bottom, the temporary wet zone is forced higher in the pot, bringing it closer to the plant’s roots and increasing the risk of root rot. Also, the gravel layer decreases the volume of growing medium, shrinking the available space for roots to grow and thrive. So, there’s clearly no advantage in doing this.
As long as a pot has holes at the base, excess water will drain away. If you want to speed this up, you can drill more holes.
Sometimes the holes get blocked by the plant’s roots, which inhibits free drainage. If you think that’s happening to your pot plant, simply push a screwdriver firmly into the holes to break up the offending roots and free it all up again, or transfer your plant into a bigger container.
The best way to improve the drainage of the mix itself is to incorporate lightweight, angular, free-draining materials such as perlite, vermiculite and composted pine bark throughout the potting mix. This will increase the number of air spaces in the mix, while also lowering the height of the temporary wet zone at the base.
Powdery mildew is a common fungal disease that affects a wide range of plants. It loves humid conditions, and you will often see it at this time of year affecting grapes, roses, sunflowers, apples, begonias, members of the cucumber family, and many others. The distinctive white or grey powdery spots can appear on leaves, stems and fruit, and when it’s left to its own devices, the disease can seriously set plants back, so you need to limit its spread. Here are some simple steps to help keep it at bay.
1 START by removing as much of the affected growth as you can. This is a huge source of fungal spores that could spread to newer parts of the plant. Also clean up fallen decaying leaves under the plant. Put all the affected material in your council green waste bin, not the compost.
2 MIX up an organic fungicide such as wettable sulfur or eco-fungicide in a pressure sprayer. Shake the container well to help dissolve the concentrate.
3 SPRAY the remaining plant thoroughly on both the upper and lower surfaces of leaves and stems. Keep an eye on the plant in the following days and continue to remove affected foliage as soon as the symptoms appear. This may keep things under control, but if you notice a build-up of disease, reapply the organic fungicide.