Pot size for mammillaria?

[brooklynbridge24]

When I bought my first bunch of cacti several months ago, I thought it would be a good idea to put them in a pot together with a fair bit of space. (I was totally new to plants and thought the tiny pots they came in would stop them growing). But now after doing a bit of research I've realized that I have probably overpotted them. They are all Mammillaria 4 - 5 cm tall and wide and I also have a single Mammillaria fragilis about 2 cm tall and 1 cm wide. What is the best pot size for them and any extra tips on how I should separate them would also be greatly appreciated.

[Aiko]

Plants should fit snuggly into a pot. Maybe enough space from plant to rim to fit your finger, maybe two fingers? For a plant with a diamter of 5 centimeters, you are probably safe with a pot size of 7 centimeters.

Although it matters how developed the root system is, or will eventually be. But that concerns the more choice cacti, which is probably less of importance to yours as I assume you got your plants from a garden centre?

[brooklynbridge24]

Thanks for the advice. I got them from the horticultural section at a local show. The man that had grown them wasn't there at the time so I couldn't ask what they were but I was told on another forum that I possibly have a Mammillaria hahniana and a Mammillaria marksiana. A third one I'm still unsure of but I'll probably post for an ID for all three to see if anyone else thinks they might be something different.

[iann]

Look at the roots, pick a pot only slightly larger, as best you can given the size of the top part. You can repot again next year, or perhaps the year after, if they rapidly outgrow that pot.

[7george]

It's up to you, I prefer small and shallow pots but it could be one common one with extra drainage.

Some growers like it big.

[DaveW]

Really, as long as not too small, pot size is irrelevant. It really depends on how quickly the potting soil dries out after watering. Smaller pots containing less potting soil usually dry out quicker, therefore it is safer not to over pot. But as with George's example, if you can get a large pot to dry out quick enough by modifying the soil to drain fast enough that is OK. Also with George's example a number of plants in a pot will usually take up the water faster and dry the soil out quicker than a single plant.

Also deeper pots drain the water away from the roots and neck of plant quicker than will a same diameter shallow pan, therefore are often dryer around the vunerable neck of our plants much quicker That may sound counter intuitive as they contain more potting soil, but is none the less true. Using the same potting soil it is therefore the pot height that determines the height of the perched water it retains, not it's diameter.

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