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Ask the Master Gardener

Cactus will need seasonal darkness to bloom

By: Trish Grenfell, Placer County Master Gardener
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Question: I purchased a Christmas cactus last Christmas so that I would have two. My other cactus was given to me by a friend who grew the plant from a cutting from her beautiful plant. 
I placed the new plant near my kitchen sink and the other one is in my living room (a room that is seldom used). The one in the living room has buds and the one in the kitchen does not. Could it have anything to do with the fact that their leaves are different? 
Answer: First of all, I believe you have two different species of holiday cacti. There are actually three species: Thanksgiving (“Schlumbergia truncate”), Christmas (“Schlumbergia x buckleyi”) and Easter (“Hatiora gaertneri”), but the Thanksgiving and Christmas cacti are similar in appearance.
There are countless hybrids and named cultivars of each species with different bloom colors that can cause confusion, but you can tell which species by the leaves, as you noted.
Thanksgiving cactus, which tends to bloom earlier, has flat leaf segments, which are prominently toothed, often with two large teeth at the tip of the last joint on each branch.
The Christmas cactus, which tends to bloom closer to Christmas, has smoother, scalloped-edge segments on somewhat drooping branches.
Inducing blooms on both species is the same. Keep the night temperatures cool (50-60 degrees F), eliminate light for 12-14 hours/day starting in September (you may have to move the plants), and reduce watering to compensate for slowed growth. Note: fertilize March to September only.
As per the photos you gave me, the Thanksgiving cactus is the one not blooming. The nighttime temperatures most likely are similar between kitchen and living room. The non-bloomer should have adequate humidity from the sink, but I am wondering if the kitchen lacks the required darkness.
The little used living room is more likely to experience natural seasonal light with its 12 hours of darkness. 
Try this: Stay out of the kitchen at night and/or go to bed earlier. You may have a few extra gifts this Christmas: a beautiful, blooming kitchen cacti, adequate sleep and a loss of a few pounds.
Have gardening questions? Call the Master Gardener hotline at (530) 889-7388.