GARDENER’S MAILBAG

Dear Neil: How can I get potted bougainvilleas to rebloom in the summer? I was advised to use a fertilizer that is high in phosphorus. I’m not sure it has helped.

That would be a logical suggestion, since phosphorus promotes roots, flowers and fruit. However, I’m not sure it’s going to help your plant. We have to water container bougainvilleas relentlessly in the summer. That does flush nutrients out of the soil in short order. They need to be replenished, but I would suggest more of a complete-and-balanced, water-soluble food. However, go light on it, perhaps at half rate and frequency. Bougainvilleas flower best when they’re rootbound and a little bit hungry.

I suspect bougainvilleas are also “short-day” plants like chrysanthemums. They need full, bright sun for 10 or 12 hours per day, but then they seem to flower most reliably when they get complete darkness for 12 or more hours at night. That’s probably why they usually bloom best in early spring and midfall.

Figuring out why a bougainvillea isn’t blooming is almost the same as why a wisteria doesn’t flower. Truth be known, it’s probably a combination of several circumstances all blended together.

Dear Neil: I’m confused as to why my loquats in South Texas froze after last winter when they survived the cold of February 2021. I don’t even know where to begin in asking my question. Do you have any input?

I saw this on several species of plants across Texas. One of the differences was that the freeze this past winter came early in the winter (the Christmas season). Plants had not quite acclimated to the upcoming cold yet. As a veteran nurseryman said to me after a damaging cold spell decades ago, “We got caught with our plants down.” The more proper horticultural term would be that the plants were not suitably “hardened.” I saw it on a lot of Asian jasmine beds, and varieties of crape myrtles that were not hurt in February 2021 were damaged quite badly in colder parts of North Texas, in 2022. The same thing happened to mondograss groundcover plantings in big parts of Texas. They were hurt this past December, but not in February 2021. Right or wrong, that would be my theory. I’ll also add that it looks like your plants may have been growing in the shade. That would weaken them over an extended period of time. That could have contributed.

Dear Neil: I bought and planted two crape myrtles five years ago. One is blooming beautifully, but the other has not bloomed. Do you have any suggestions of what the cause might be?

I work with crape myrtles many hours each week as part of a community organization to which I belong. We have planted more than 40,000 in our hometown. In the 50 years I’ve been growing crape myrtles I can give you the following possible reasons for a plant not to bloom. Since I don’t have a photo or all the facts, I’ll have to leave it up to you to sort through this list.

Your plants could be different varieties. There are more than 130 named varieties, and they behave differently. Some varieties put out their first round of blooms, for example, in late April or early May. Others don’t bloom until mid-July.

Crape myrtles require full sun, constantly moist soil, and a ready supply of nitrogen to promote new growth. Their flower buds form on the new growth. If there isn’t any new growth, blooms will be sparse. I’ve been looking at scores of crape myrtles in schoolyards in our town. They haven’t been fed or watered in several summers, and I was just pointing out to my wife this week how delayed they are in producing their flowers compared to the large and lovely mature plants of the same varieties in well-maintained home landscapes just a block or two away.

Crape myrtles must never be topped. Pruning last year’s shoots off the branches sets the plants back dramatically. Plus, it ruins their natural growth form.

The one plant may have suffered freeze damage in February 2021 and December 2022. Varieties Natchez, Tuscarora, Muskogee, Sioux, Country Red and a handful of others were damaged or killed to the ground by the freeze. They are notoriously tender in parts of Texas. They will eventually bloom on their regrowth, but it will take a while.

Have a question you’d like Neil to consider? E-mail him at mailbag@sperrygardens. com. Neil regrets that he cannot reply to questions individually.