Question
I have a small (6" tall) Mammillaria polythele. For some reason, it is not the deep, dark green color that I have seen in other cacti of this type.

I have read a great deal about caring for cacti...I have it planted in a 4.3" clay pot, in Schultz's Cactus & Succulent potting mix. I only water it when the soil is completely dry. I check the moisture level with a wooden skewer stick. It only gets watered about once every 3 to 4 weeks. I give it Schultz's Cactus Plus liquid plant food every other watering. The directions say you can give this food to a cactus every time you water it, but I feel that would be too much.

The problem is that my cactus seems to be a slightly yellowish color. There is slight wrinkling at the base of it; the wrinkles seem to be a very light brown color. Also, there are 14 nice, little red sprouts which I believe would have been flowers near the top of it...they seem to be very dry, as if they are about to dry up.

I am thinking this is a problem with too much sunlight. I have been putting it outside 2 or 3 nights a week on nice days (later in the day when the sun is not so strong) for a couple of hours at a time this past summer, thinking it would like the sun. Have I been slow roasting my plant? Would just keeping it out of sunlight restore it's color and get rid of the wrinkling? Or do you think this has to do with feeding it every 4 to 6 weeks? The Schultz cactus food seems to be very mild, so I did not think it would be bad to feed it according to the instructions.

I did decide to buy a light fixture and use full-spectrum compact fluorescent bulbs to keep my cacti under. The bulbs are very good...rated at 5900 K...a CRI of 94+...and the bulb is rated at 1150 lumens. I had planned on giving my cacti about 10 to 20 hours a week or so under this bulb. Would this be a better idea to take care of the cactus's lighting needs?

I'm sorry for being so wordy...but I wanted to include as much detail as I could think of. Could you please tell me the symptoms a cactus will show when it is getting too much water, food, and sunlight? I think that would help me in caring for my cacti and preventing this from happening again. Also, do cacti generally dislike humid, very warm rooms? If I move my cacti away from the windows to avoid direct sunlight, most of the rooms of my house are rather warm & humid. 厀ould this be bad for them? Is an air- conditioned room bad for them also?

I thank you most sincerely for your time Greg!

Tom K.

Answer
Tom,

Judging from some of the photos at this website: http://www.mammillarias.net/gallery/mammillaria_species.php?searchstring=polythe...
, what you are describing my be normal. However, Mammallarias should not get any direct sun. In the wild they usually grow under something (tall grasses, bushes, etc). The grow bulb is a good idea. Your watering seems to be good. Most cacti prefer some humidity, but most will do well in a dry environment as well. However, without proper lighting, most cacti do not make good house plants. Hope this helps. If I missed a question, please reply to my answer.

Sincerely,

Greg