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Garden Detective: Plumeria, hydrangea and flowering plum

A beautiful example of a pink Lacecap Hydrangea

A beautiful example of a pink Lacecap Hydrangea flower. (Hydrangea macrophylla normalis) Credit: Getty Images/Ken Wiedemann

DEAR JESSICA: I read your column every Sunday and learn so much. I have a plumeria growing in a clay pot, which I kept out on the deck all summer, where it thrived. How can I keep it alive as temperatures get cooler? Last year, I kept it in the kitchen, and it stayed dormant with few leaves. It has really matured since then, so any advice would be helpful. — Lisa Schwartz, Syosset

DEAR LISA: Plumeria, also known as frangipani, is best known as the sweetly scented flower used for making Hawaiian leis. I remember being hit with their scent immediately upon exiting the airport in Honolulu and when walking near Waikiki Beach while vacationing there several years ago. With proper care, it's definitely possible to keep these plants alive indoors.

For best results, Plumeria should be potted in a well-draining medium composed of equal parts peat moss and perlite (or a commercially prepared cactus potting mix) in a container that has drainage holes in its bottom. Place the plant where it will receive at least six hours of bright sunlight (or 15 hours of fluorescent light) daily. Water well, but only when the soil is dry; ascertain this by sticking your finger into the soil up to the second knuckle.

As a tropical plant, Plumeria requires warmth and thrives best at 80 to 90 degrees, but can get by at 75 indoors during the day (and no cooler than 60 overnight).

Gradually transition the plant back outdoors around Memorial Day and apply a high-phosphorus 10-50-10 fertilizer twice a week during spring and summer to promote blooming.

DEAR JESSICA: I have a thriving lacecap hydrangea up front of my house. I wish to control its size. How much can I cut, and when can I do it? — Mary Jane Behrenfeld, Plainview

DEAR MARY JANE: It's too late this year to prune your hydrangea — your lacecap is a Macrophylla, so it should be pruned only at the end of summer, right after its flowers fade. After that, it forms buds that will become next year's flowers, so pruning it now would result in diminished (or absent) blooms next year.

When you do prune it, you can thin it out by cutting some branches down to the ground and/or trim them by one-third or one-half to shorten their height, but they will just grow back. You might instead opt to divide it, or move it altogether and plant a smaller-growing variety in its place.

You can divide it now or in very early spring, when buds begin to swell, by digging it up and separating the roots into two or three pieces, then replanting each separately. The best time to relocate hydrangeas is in mid- to late-fall, after their leaves have fallen and they’ve entered dormancy.

DEAR JESSICA: I am a loyal reader of your column, and I have question: When is the best time to prune decorative flowering plum trees? Will pruning now affect the spring blooms? — Kevin Conologue, Massapequa

DEAR KEVIN: Yes, pruning now would be a mistake, as there simply isn’t enough time for a wound to heal before frost sets in and the tree goes dormant. The exception to this is removing individual branches that are dead, diseased, broken or otherwise weak. That can be done at any time, and in fact should be done, if necessary in fall, to avoid damage to people and property during winter storms.

For maintenance or rejuvenative pruning, however, ornamental trees, such as plums that bloom in spring, shouldn’t be pruned until after their flowers have dropped. Trees that bloom in summer should be pruned in late winter or early spring.

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