Astrophytum developed spots

[.ilUli.]

Can someone tell me what these tan spots are and how I should treat them?

[MikeInOz]

The pebbles will not allow you to gage the moisture of the substrate. Until you are experienced enough to just ''know'' they need water without even looking, I suggest removing the stones and waiting for at least the top half of the mix to be be completely dry before watering again. A sharpened chop stick will help you determine. It's remarkable just how long moisture remains in the depths of the mix even during hot weather. I find too much water in the mix is the cause of most marks on cacti, and in the winter, too much humidity along with cold temps.

[Steve Johnson]

The pebbles will not allow you to gage the moisture of the substrate. Until you are experienced enough to just ''know'' they need water without even looking, I suggest removing the stones and waiting for at least the top half of the mix to be be completely dry before watering again. A sharpened chop stick will help you determine. It's remarkable just how long moisture remains in the depths of the mix even during hot weather. I find too much water in the mix is the cause of most marks on cacti, and in the winter, too much humidity along with cold temps.

Agreed, although I'll go one step further -- of the Astrophytums I grow (asterias, capricorne, 'capristigma' hybrid, and myriostigma), myriostigma is the only Astro that really doesn't like the constant all-year humidity in my area. I'm growing 64 of my 68 cacti in a pumice-granite gravel mix (no soil), I let their roots dry out completely between waterings, and even that isn't enough to prevent more of those spots from appearing on my myriostigma every year. If your part of Orange County is as constantly humid as mine (I live near Baldwin Hills), the callused-over water blisters you see on your plant may be unavoidable. Unsightly yes, but they're certainly not life-threatening.

[.ilUli.]

Agreed, although I'll go one step further -- of the Astrophytums I grow (asterias, capricorne, 'capristigma' hybrid, and myriostigma), myriostigma is the only Astro that really doesn't like the constant all-year humidity in my area. I'm growing 64 of my 68 cacti in a pumice-granite gravel mix (no soil), I let their roots dry out completely between waterings, and even that isn't enough to prevent more of those spots from appearing on my myriostigma every year. If your part of Orange County is as constantly humid as mine (I live near Baldwin Hills), the callused-over water blisters you see on your plant may be unavoidable. Unsightly yes, but they're certainly not life-threatening.

It has been a humid summer, quite different from others. Every morning I find dew on my cacti, and the days are steamier than usual. I think I err on the side of caution and wait a bit extra before watering (I usually go by the weight of the pots in addition to how the cacti look and what I know about their requirements) but obviously this one is telling me I'm off.

[greenknight]

I like to stick in some larger rocks where there's space, you can easily pick one up and check under it for moisture. Much easier than digging through a layer of pebbles.