This spring I am mixing it up and going for a new soil-less Hibiscus potting mix recipe. Because I grow in a greenhouse, and because our winters are cold, my Hibiscus have a tendency to get wet feet and develop wilt disease. Old compacted potting soil and poor porosity of the soil to drain sufficient water are the main causes of wilt disease.
Why is good drainage important?
Hibiscus don’t like, what is called, “wet feet”. Meaning that the soil shouldn’t remain sodden and should drain away as much water as possible. The roots are susceptible to bad soil-borne fungus that infect the plant causing wilt disease. Wilt disease is a fungal infection where the fungus enters the plant and blocks vital capillaries from transporting water and nutrients around the plant. It’s usually fatal, but I’ve manage to save quite a few from this disease through quick identification and treatment.
However, prevention is better than reaction which is why I am changing the soil mix to try to stop this issue. The image on the right is of an El Capitolio Sport which hasn’t suffered wilt disease this year. It did have compacted anaerobic soil resulting in leaf drop and overall poor health over winter. The photo shows it repotted in soil-less potting mix.
But why would I mix my own potting soil?
It’s a good question. The problem with ready-made bags of potting mix is they often contain materials that aren’t good for Hibiscus plants. Some contain a slow-release fertiliser that contains too much Phosphorus. Hibiscus can’t tolerate phosphorous in high quantities, or they simply contain substandard ingredients.
When you mix your own potting soil you ensure a tighter control over the ingredients, enabling you to better control over soil porosity, nutrients and soil ph.
Hibiscus like slightly acid soil, around 5.5-6 on the ph scale. Home centre potting mixes are usually ph neutral.
Soil-less hibiscus potting mix recipe
- 2 parts coco coir
- 2 parts organic cow manure
- a desired amount hardwood chips, various sizes
- 1 part washed river sand
- 1 part perlite
Mix all parts together thoroughly. The coco coir should be rehydrated prior to mixing.
Coco Coir vs peat
I’ve never been a fan of peat. Peat is hard to rewet when dry, it degrades, and will hold too much water. It also isn’t environmentally sustainable. Coco coir on the other hand, is environmentally sustainable. It’s made from a waste product form the coconut industry, coconut husks. It’s water retention is good but not too high, it’s airy so the roots get oxygen. And it helps hold nutrients in the pot rather than having them wash out every time you water. If you’re using peat, I’d recommend giving coco coir a try as a substitute.
But the biggest benefit is that coco coir contains potassium. And as we know, potassium is one element that Hibiscus need to grow healthy.
Try this soil-less hibiscus potting mix recipe and don’t forget to journal your repotting efforts to track the results.