Mammillaria polythele Yellow/Wrinkly: Likely Too Much Sun, Not Food

Small Mammillaria: Yellowish, Wrinkled Base, Dry Red Buds—Sun or Fertilizer?

Owner details care: 4.3" clay pot, cactus mix, water every 3–4 weeks when dry, fertilize every other watering. Gets 2–3 hrs outdoor sun 2–3x/week summer. Plans 10–20 hrs/week under 5900K CFL. Asks symptoms of excess water/food/sun, and if warm humid rooms are bad.

Greg's Assessment

• Photos suggest appearance may be normal for species.
• Mammillarias need NO direct sun—grow under grasses/bushes in wild.
• Grow bulb is good idea.
• Watering seems fine.
• Most cacti tolerate dry air; without good light, poor houseplants.

Stop outdoor sun; use artificial light. Humidity not a major issue.