Thanks to the magic of WordPress, I am able to see a list of the search terms used by readers coming to Gardening in the Mud. While I try my best to anticipate questions or issues in writing each post, I don’t necessarily try to cover every aspect of a particular plant. That’s why there’s an opportunity to make comments or ask questions in each post. Still, I understand that not everyone is comfortable participating in a blog, so here are some answers to specific search queries:
Physocarpus: White fungus on Physocarpus
Yes, Physocarpus is susceptible to mildew. If you are experiencing mildew on a newly purchased plant, take your receipt (and a digital photo, if you can) back to the place where you purchased the shrub and request a refund. Mildew overwinters in dead leaves and can also overwinter in branches. A newly planted shrub with a mildew problem means that the vendor purchased stock from a careless nursery. Always purchase plants from a reputable merchant.
If your plant is suddenly showing signs of mildew, even though there were no previous problems, consider the following solutions:
• Thin out the Physocarpus to improve air circulation. Don’t be timid—remove entire branches if the plant has become too overgrown. (I prune my shrub at least three times a season because it grows so quickly.)
• Move the plant to an area with increased airflow and/or more sun.
• Rake up and destroy all fallen leaves—do not compost the leaves.
• If you want to fertilize the plant, use a fertilizer with very low nitrogen. Overly succulent leaves, caused by excessive nitrogen application, promote disease and encourage insect attacks.
Taxus: 1) White fungus, 2) Yellow needles
1) If you see what you think is a white fungus on your yew, check a little closer: it’s probably a cluster of Taxus Mealybug located in the crotches of the shrub. To control the mealybugs, spray with insecticidal soap, and be sure to drench the insects.
2) A few yellow needles on the ends of branches after winter are not uncommon. Unless you have extremely alkaline soil (pH of 7.5 or more), chances are that your yew is drowning: either it’s situated right near a drainpipe by the side of the house, or the yew is planted in poorly draining soil, or you are overwatering the yew. To solve the problem, either move the yew, improve the planting conditions, or stop watering (yews really don’t need more water than what occurs naturally throughout the year—unless there is a prolonged drought).
Annuals: Can annuals be cut back?
No. Annuals complete their lives in one growing season. Cutting them back will not encourage re-blooming. Some annuals, such as Pelargoniums (Geraniums) can benefit from being pinched back early in the season to promote more branching, a more compact habit and larger blooms, but, pinching back a plant merely releases hormones that affect the plant’s growth habit. Otherwise, just keep the annual deadheaded to encourage prolonged bloom.
Perennials: Should perennials be fertilized after blooming?
A small amount of organic or balanced fertilizer (5-5-5) applied after blooming probably won’t hurt the plant and may be beneficial. However, you don’t want to encourage new growth late in the season unless the plant is a re-bloomer. Definitely avoid post-bloom fertilization for perennials that flower in August, September or later.
Anemones: Yellowing leaves
Yellowing leaves at the bottom of a plant usually indicate too much water or too little nitrogen.
Buxus: White fungus on boxwood
What appears to be a fungus is actually the white, waxy exudate produced by Boxwood Psyllid nymphs. The best time to control the psyllids is in early May when the nymphs are active, at which time you can drench the insects in insecticidal soap or a very light horticultural oil (follow directions on the package precisely). Once the psyllids have matured, your only option is to use acephate, a systemic insecticide which is highly effective but requires very careful handling.
Geums: Different colors on same plant
Most Geum cultivars are hybrids, meaning that they are bred from parents with different characteristics, including color. Sometimes, flowers do what is called “sporting back”—they revert back to one or another of the parents rather than maintaining their hybridization. I once planted seven identical peonies in a raised bed next to my garage, and every single plant sported back to the parents. The effect was quite spectacular, since I had dark red, palest pink and medium pink blooms all at the same time.
Itea virginica ‘Little Henry’: When to prune
Suckers can be pruned out at any time. Wait to prune out deadwood after the winter until the leaves have fully formed. For general pruning, shape the plant immediately after flowering. Pruning at any other time is likely to result in a loss of flowers for either the current season or the next season.