The height of summer in New Hampshire brings incredible bargains for gardeners looking to add to their collections with plants, shrubs and trees, but bringing in new plants when temperatures are high and rain is scarce comes with both risks and rewards.

Drive by any garden center or nursery these days, and you’ll be tempted by signs offering trees, plants and shrubs at reduced prices. But Margaret Hagen of the University of New Hampshire Cooperative Extension warns to be careful before jumping on those bargains.

Mid-summer sales often slash prices on plants, she said, “However, even at half price I would be sure to buy sale plants at a garden center where you know that they’ve been pruned, watered and fertilized when necessary.”

“If the plants you buy are not in good shape, it may take so long to nurse them back to good health that the growing season is almost over before they look good,” she said.

Hagen said garden centers put annuals on sale when they are combining smaller plants left over from the spring to fill larger pots for people who prefer to buy well-established plants. The sales also come to reduce inventory to make room for fall plants like mums that come in during late July.

Just because they’re on sale doesn’t mean the plants are in bad shape. Garden centers and nurseries who take good care of their plants, water them regularly and do what’s necessary to keep them healthy simply have to keep their stock moving.

“As for trees and shrubs, the same applies,” said Hagen. “If you know that the plants have had good care, then by all means, purchase them.”

This time of year, she said, plants in containers will adjust most easily to the weather and soil conditions whereas plants sold balled and wrapped in burlap will do better if planted when it is a little cooler in the fall and spring.

But the most important factor for bringing in new plants as the dog days approach is water, and lately, there hasn’t been a lot of that falling from the sky.

“All plants need approximately one inch of precipitation every seven to 10 days,” said Hagen. “For the most part we have not had any significant rain since July 4, except for thundershowers.”

Newly planted trees and shrubs need to get that one inch of water per week religiously for the first two years after they are planted to make sure that they send out plenty of new roots and become well established.

nfoster@newstote.com