Do Sempervivum Need a More Organic Soil?

westes Zone 9b California SF Bay
5 months ago
last modified: 5 months ago

Sempervivum are alpine rock garden succulents that grow shallow roots in small amounts of soil. I have had problems getting these to flourish in mixes that do not have some rich organic component. What kinds of soil mixes have you had success with?

With traditional gritty mix, these plants eventually root and grow, but the growth is not abundant without regular synthetic fertilizer. In studying the soil mixes that professional growers have published online, I could not help but notice that many of them are using clay in the soil mix. Sempervivivums By Post in the UK is using 3 parts of John Innes #3 soil with one part of grit. I researched components of the Innes #3 and by my calculations the resulting mix is about 44% clay loam soil. And this is a container mix!

Sempervivums By Post grows some of the healthiest looking plants I have ever seen in this genus. The attached photo is their container planting.

Another grower I found starts with clay loam soil and adds sand to that.

The only thing that I can think of to explain these results is that these plants must like some component of the soil to have a very high CEC, even though they are not heavy feeders (supposedly). In addition, they seem to like a neutral pH, so they probably are not doing as well in soils with too much peat and bark.

Does anyone have insights as to why this genus of succulent does so well in soils with some amount of clay?

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