Cactus ID

(Question)

Hi! I received this cactus as a gift and am wondering if anyone could help me identify it. I’ve searched a while myself and can’t seem to figure it out. Since I don’t know what it’s supposed to look like, I can’t tell how well it’s doing (I assume it’s not supposed to be brown on the bottom?) It’s potted in cactus potting soil and gravel, and sits on a south facing windowsill with a leaky window (so it’s bright but cold in the winter). It has a growth on the top that I can’t tell if it is growing another part to itself or trying to bud (if that makes sense). I’ve never seen it flower and I’m not sure if it does. The spines seem to be white but with reddish ends on the new growth, and are very sharp. It also has a whitish powder on it that I’m not sure if it’s pollen or disease or dust. Any idea what kind of cactus this is?

 

 

(Answer)

I think your cactus appears to be a Mammillaria.  This genus has over 200 species so it is difficult to tell which exact one from the pictures.  Care for most of these plants is the same anyway.

The brown at the bottom may be related to overwatering.  In winter the plant is dormant and therefore should be only watered enough to keep it from shrivelling.  This is usually about once per month.  The best potting medium to use is a soilless mix, with no peat moss, combined with the cactus potting soil. A south facing window is the best exposure as long as the temperature doesn’t go lower than 15.5 degrees Celsius in the daytime and 7 degrees Celsius at night, it should be okay.

The whitish powder on the top might be mealy bugs which are a common pest affecting cacti.  Try using a Q-tip with 70% rubbing alcohol, if the white comes away it will be the bug.  You can continue to remove mealy bugs by this method.  In order to minimize spread of the bugs, move the cactus away from other plants.  For more information about caring for cacti, please review the link below:

Guide to growing cacti and other succulents