| For the Times-Union
In lieu of starting with a question this month, let’s start with a “must-do” for this weekend.
If you have a Christmas cactus that you’re counting on being spectacular during the holiday season, this is the time — in fact, the latest time — to start getting your plant ready.
Christmas cactus is like poinsettia and chrysanthemum in that it blooms in response to shorter days and cooler temperatures. Since our homes are filled with artificial light and are likely climate-controlled, we have to be good plant parents and provide the Christmas cactus with its preferred conditions. In other words, we need to start tucking it in for the night in a dark, cool place. If you start today placing your Christmas cactus in a closet every day from 5 p.m. to 8 a.m. for six weeks, then, in ten weeks, it should flower. That makes it right around Christmas day.
As a reminder, bud drop is common and usually the result of a change in environment, especially a change to warmer temperatures. Therefore, don’t place the plant in a draft or near a heat source. Christmas cactus like it a little cooler than many homes are kept. The ideal temperature ranges are 65-75 degrees during the day and 50-60 degrees at night.
When you’re ready to display it, keep the Christmas cactus in bright, indirect light, or under an incandescent or fluorescent lamp if the room is dim.
In its native Brazil, Christmas cactus, a variety of true tropical cacti, grows in areas of heavy moisture and high humidity. They aren’t as drought-tolerant as their desert relatives and, in fact, may drop flower buds if the soil gets too dry — exactly what you’ve been working to prevent. Keep an eye on them and water when the top inch of soil feels dry. Allow it to drain thoroughly, pouring off any excess water in the pot’s saucer.
Following flowering, Christmas cacti usually put on new growth. This is the best time to prune the plant to force branching. If you do it again in late spring, you’ll have even more flowering branches next holiday season.
Some of the leaves on my crape myrtle have white powdery spots. Some of the leaves are completely coated with a dusty white substance. I’ve heard of “powdery mildew” and “downy mildew.” Could this be one of those diseases? What should I do about it?
Though both these fungal diseases have “mildew” in the common name, they aren’t the same problem at all and will require different treatments to solve them. It’s important, then, that you know the differences in symptoms of powdery mildew and downy mildew.
With powdery mildew, you’ll find circular white fungal spots on plant shoots and anywhere on the leaf surface. After the fungus has been present for a while, the leaves will become yellow.
Fungal spots of downy mildew are angular, more gray than white and will appear only by the leaf veins. Yellow leaves may appear before other symptoms of the fungus are evident.
Of course, the primary reason we plant crape myrtle is their spectacular floral display each summer. In addition to their beauty, they are also relatively low-maintenance with few pest problems. Unfortunately, powdery mildew is a common problem for varieties not bred to be resistant to this fungus.
This year’s rainfall has been somewhat spotty depending on where you live. Heat and humidity, though, have been unquestionably high everywhere. This has created the perfect environment for powdery mildew to thrive in shady areas where plants are crowded.
Though powdery mildew is seldom fatal for the tree, it is a serious problem in both spring and fall. The fungus robs the plant of nutrients, resulting in stunted and curled leaves, and dwarfed buds and fruits. It can completely cover and severely damage new growth, while older leaves are less likely to be affected. Severe infection also causes premature defoliation.
Both types of mildews can be treated successfully with fungicide, either natural or synthetic. Natural fungicides such as neem oil, sulfur and potassium bicarbonate are effective when used correctly. Whichever you choose, be sure the product label specifically lists powdery mildew as a disease for which it is effective. As always, read and follow all instructions and precautions on the label.
While fungicides are a good treatment choice during spring and summer, you have another option in the fall. Simply allow the infected leaves to fall, rake them up and dispose of them. Don’t allow the fungus to overwinter in the debris around the tree.
If your plans include adding more crape myrtle to your garden, select one that is resistant to fungal disease (blogs.ifas.ufl.edu/nassauco/2017/03/03/crape-myrtles-resistant-to-powdery-mildew/). Plant them in full sun with enough space around them to provide good air circulation.
For more information on selection, planting, and care of crape myrtle trees, go to the UF publication, “Crape Myrtle in Florida” (edis.ifas.ufl.edu/mg266).
Paula Weatherby is a Master Gardener Volunteer with the Duval County Extension Service and the University of Florida/IFAS. For gardening questions, call the Duval County Extension Office at (904) 255-7450 from 9 a.m. to noon and 12:30 to 3:30 p.m. Monday-Friday and ask for a Master Gardener Volunteer.