Friday, December 12, 2008
The care of a Christmas cactus
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
Dear John
5102 Greenfield St. SW
Roanoke, Va. 24018
Or send an e-mail. Answers will be given only in this column. Please don't send pictures or samples.
Recent columns
Q: We were given a dense pink-orange Christmas cactus hanging basket by our son during the holiday season from the garden center of a local home improvement center a few years ago. We hung it in the north-facing window of our master bathroom during the winters and have hung it outside on the north side of our house during summers. It seemed to do OK for the first year or two, but then branches began breaking off as if the plant was becoming very weak. I repotted it and added some perlite to our favorite Sunshine Mix potting soil. I still used a hanging basket pot for the plant. My spouse said that there must be something eating the insides of the plant. I couldn’t see any borer holes or tunnels. The plant bloomed early this year, but it looks pathetic. The soil seems to stay wet for long periods of time. What is happening and what should we do? I know that using insecticides on indoor plants is not recommended and using fungicides on plants in the house is not suggested either.
A: It sounds like your Christmas cactus suffers from root and stem rot, and not from any insect invasion. I don’t know of any borer that can infest a Christmas cactus.
The problem could have started when you placed it in low light indoors during past winters in that north-facing window. They need to have full sunshine during the winters.
The first thing that I would do is to carefully knock the plant out of its pot and examine the roots. If you find only a very small system of firm, light brown roots, it might be too late.
If you have to toss it, start a new plant by taking small cuttings to root in damp sand from shoot ends that are not shriveled or limp.
You could try repotting the wizened plant in a small pot just slightly wider than what good roots are left. Put broken pieces of clay pots or pea gravel in the bottom to create good drainage. Use a potting mix of sandy soil that is sold in bags for desert cactuses mixed with an equal amount of roughly chopped sphagnum moss, which is also sold by the bag. Sphagnum is supposed to have some natural anti-fungus properties.
Place this in full winter sunshine and touch the potting soil to feel for a need for moisture frequently. Water only when the soil mix feels dry to the touch, but don’t let it go bone dry for very long during the growing season.
Once you see new green shoots emerging from the ends of the branches or from the base of the plant, begin fertilizing with a water-mixable fertilizer for potted plants that provides nitrogen, phosphorus, and potassium. Be sure to follow fertilizer instructions for the amount to mix per amount of water so that plant parts will not be injured. Do this once per month until late summer when you’ll also begin watering less frequently.
Move it outside to a bright location with no direct sun this spring once the night temperatures are in the mid-50s. Leave the plant outside after fertilizing is discontinued until the night temperatures fall back into the 40s.
