Ask the Gardener: Life is too short for boring trees

Q: On a trip to Serbia last fall, our guide gave me a horse chestnut pod and said that it could be used to protect stored woolens from moths. She said she’d find more for me during the tour. That never happened (too many other things to do!). I don’t recall if she said that it had to be pierced, or used as-is.

Do you know anything about this? If so, where can I find horse chestnut trees in Raleigh or Durham?

A: The tree you saw in Serbia was the common or European horse hestnut, Aesculus hippocastanum, a large growing tree wild in Albania, Bulgaria, Greece and the states of what was formerly Yugoslavia. The genus Aesculus is found across North America, Europe, India, China and Japan. The North American species are known as buckeyes, while the rest are generally called horse chestnuts.

Horse chestnuts bear large palmately compound leaves resembling a hand with all the leaflets (fingers) joined in the center. The flowers are quite showy, and on the European horse chestnut are held in clusters of more than 200 individual white flowers. As the flowers age they become creamy yellow, then pink. Ultimately they will form large glossy brown fruit held in thick, prickly husks.

The glossy brown seeds can be 2 inches or so in diameter and are the source of the reputed moth deterrent as they contain the natural repellent chemical triterpenoid saponin. When used as a moth deterrent, they are typically pierced through and hung on a string in a wardrobe or closet. Seeds used in this way must be changed each year to remain effective.

Horse chestnuts and buckeyes are widely grown in the United States, and several species can certainly be found in the area botanical gardens. The European species prefers a colder winter and less humid summer to perform its best, although it will grow in central North Carolina. In most summers here, the plants will suffer from a leaf blotch disease that discolors the foliage and causes it to drop early, often as early as mid-July, making it of limited use in our area.

Q: My azaleas have grown way too big. Can I prune them back now and still have flowers next spring?

A: Now is not the time to prune your azaleas if you still would like them to flower next spring. Spring bloomers develop the next season’s flower buds during the summer. As a general rule, any trees or shrubs that flower in the spring should be pruned within about 30 days after they finish blossoming to ensure plenty of time for them to develop next year’s flower buds.

Summer blooming plants can mostly be pruned during the winter or early spring since they typically develop flower buds on the new season’s growth. One exception is the bigleaf hydrangeas (Hydrangea macrophylla). These plants mostly flower on new growth emerging from old growth, so pruning them back hard in winter will reduce flowering significantly. Instead of pruning hard, remove about one-third of the oldest branches at the base to open up overgrown and congested plants. Alternatively, if your plant has just gotten too tall, look on the stems for the large, swollen buds over the winter. Prune the stems back to just above the third large bud down the stem. This will leave plenty of old growth to ensure flowering over the summer.

This story was originally published September 10, 2015 at 1:03 PM with the headline "Ask the Gardener: Life is too short for boring trees."