New to cacti - is mine OK?

[Navegador]

Hi everyone, this is my first post here so please bear with a me a little.

A few months ago my old man gave me what I seems to be a Mammillaria elongata, judging from internet photos. In any case it came planted in very dark peaty soil in a small mug with no drainage holes, so it obviously needed repotting and better soil.

I repotted my Mammillaria on the 15th of June. From the photos you'll see it's "overpotted" but that was what I had available, the mug was taller so anything smaller was too short for the existing roots and the pot I chose has lots of drain holes. As you can also see from the photo below the plant lives in a window sill that faces east, which means lots of direct sunlight in the morning (from about 6:00 to about 11:30 a.m.). I turn it a diferente direction every morning, not sure if that's a good idea but it keeps the cactus straight.

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I'm in Rio de Janeiro and it's Winter over here. That means temperatures stay between 15 and 25 deg.C with lots of foggy, kinda dark days. In terms of sunlight hours, in the tropics there's maybe a one hour difference between winter and summer so in theory there's plenty of light (photo above was taken in the afternoon).

I waited a few days before watering the cactus after I planted it and have been watering every 15-20 days. Something that worries me is, even though the soil drains quickly (almost immediately in fact), it stays moist for at least a week after watering. Below the very top layer, it takes about 10-15 days to dry. I used a mix of coarsely ground dolomite, and a mix of what looks like carbonized rice chaff, earthworm humus and regular potting soil that came bagged with the pot. I tried to make as loose a mix as I could.

It's been 75 days since I repotted and the cactus is showing lots of new shoots (see below). Is that a sign of stress or does my plant look healthy?

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Also, I've noticed that it's grown roots that are showing up in the surface. I'm guessing that, since the soil compacted a bit (with regular watering), maybe it's too compact and is turning/has turned into a sort of concrete (I guess the dolomite grit didn't help there) and the roots are searching loose soil close to the surface? Or maybe I'm wrong the soil and the plant are just fine.

Anyway there are more pictures here. The first seven are from "day zero" and the rest are from the morning of day 75 after repotting. Day 75 photos look dark because we had heavy fog this morning and the light threw my camera's white balance off a bit.

Please check them out, some show the surface roots I mentioned, and let me know what you think.

I also cut some shoots to try and root them but that's the subject of a future post.

Thank you and sorry about the long post!

[greenknight]

Yes, it's Mammillaria elongata, and it looks healthy. Lots of branching is normal for the species. It could take more sun - that would produce denser spine coverage and more color - but it's getting enough light for healthy growth. I don't think the exposed roots are any problem, either - this is a shallow-rooted species, likely just the settling of the soil when you watered left some roots uncovered.

The soil remaining moist for a week is not a problem, either, as long as you're aware of it and are waiting until it dries before you water. You don't want the soil to stay saturated for long, but just damp is okay.

The potting mix is a bit unusual. Carbonized rice hulls? Sure, why not - both rice hulls and biochar (carbonized plant matter) are reported to work well, so it should be fine. Dolomite grit is okay, except that it's a form of limestone - it makes the soil alkaline. North American species are okay with that (and this one's from Mexico), but South American species don't like it. Some growers use limestone for species that naturally grow in it, while others say it just makes for slower growth, and avoid it completely. Your cactus is growing well, though, I don't think you need to change anything for now.

[DaveW]

I would not call that over potted and with offsetting species you have to allow more pot space for the offsets to grow out more or less horizontally.

As with all things if it's growing OK, it is OK, on the premise "if it aint broke don't fix it".

[Navegador]

Thanks for the replies.

About colour & sunlight exposure, the plant lives behind a double glazed window, maybe that's the problem. I'll try to leave it outside (on top of the AC unit) for short periods and see what happens, but it can't really live outside permanently; my building forbids it, Rio's weather is too wet and there's lots of insects and birds around!