Homegrown: Petunias, rose shrubs

I have some petunias that I kept indoors over the winter. They have developed a cream-colored, almost sandy-feeling substance on them. What is it and what should I do?

— Michelle

I’m not sure what’s going on with your plant. Most people don’t realize that petunias (at least most of them) are a tropical perennial. We grow them as annuals here because they won’t survive our cold winters. They make difficult houseplants. They don’t get enough light unless you have a greenhouse and there are a number of insect and disease problems that can plague them in that sort of environment.

It may be that your plant has powdery mildew or whitefly or something else like that going on. On the other hand, petunias have a natural stickiness to the leaves. It could be that material has just built up on the foliage, causing what you’re seeing.

I’d give the plant a good cleaning by putting it in the sink and washing the leaves off thoroughly with tepid water. You don’t have to scrub them, just use your hands or a soft cloth. I’d also move the plant outdoors, at least during the day. It will be a lot happier there than in the house. You can scoot it indoors if they’re calling for a frosty night but hopefully, we’re past all that.

I have several rose shrubs that have struggled this last year. They have lots of dead branches as well as some new growth. Can I cut them back to about a foot and a half or do they need to be pruned like a regular rose bush?

— Thank you, Teresa

Shrub roses can be pruned like a standard hybrid rose but you don’t have to, and you don’t have to do it every year. I would definitely start by removing any dead growth on the plant; doing that will help clean things up a lot and simplify your pruning. You should then remove any crossing or competing canes. Where rose canes rub against each other, large wounds will develop creating a prime opportunity for insect and disease problems to get started.

Cutting the plant back to a foot or two is fine. I pruned some shrub roses in my yard this spring ,and I took them back to about 12 inches. Cutting just above an outward-facing bud is good practice because it helps to spread and open the plant out a bit, but it’s not imperative with a shrub rose. Their superior resistance to powdery mildew makes it less important to prune the plant to improve air circulation within it.

Just be sure to paint the cut cane ends with black pruning paint to prevent cane borers from getting in them.

Our tomato plants and pepper plants turned white soon after being planted outside.

— Nancy

 

I think what you’re seeing is just the plant reacting to being planted outside. Whenever you’re moving a plant from inside the house or a greenhouse, I think it’s a good idea to “harden off” the plants first. This is a process of getting them used to the conditions outdoors because they’re used to the more benign conditions of inside where they’re protected from the extremes of temperature, humidity and wind outside.

To do this, put the plants in a shady spot outside during the day and bring them inside at night. Doing this for three or four days will slow them down a bit and get them ready for life in the great outdoors. I think we’re seeing a bit more of this with our cooler, later spring weather this year. At this point, just hang in with the plants. They should recover and start growing soon.


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