Q. A friend gave me a couple of peony plants three years ago. They are planted in full sun, and they look healthy, but they don’t bloom. I know they can take a while to get established, but isn’t three years enough? What else could be wrong?

A. A few things can cause peonies to fail to bloom.

Sometimes flower buds are affected by fungal diseases or insects. You should be able to see this; buds will be distorted or rotted. There’s not a lot you can do about the insect pests, but if the bulbs have a fungal disease, as can sometimes happen in a cool, wet, spring, it’s a good idea to remove the dead buds and any diseased foliage to help keep the same pathogens from affecting the plant the next year.

Usually, though, when peonies don’t bloom it’s not because of pests or disease, but because of some other factor in their environment – heat, cold, too much fertilizer, a less-than-optimal planting site, or being planted too deep.

In spring, bulbs can killed by a late frost. Hot, dry summers can affect peonies, too, causing them to bloom poorly the following year. Hot, dry summers tend to be in short supply in the northland, though, so unless you have your peonies planted in a very hot location, such as next to a lot of pavement, I’d suspect one of the other cultural problems.

Too much shade can cause buds to fail to open, or can make the plant fail to produce buds at all. Peonies need 6-8 hours of sun, but it sounds like yours are getting at least that much, so that doesn’t seem to be your culprit, either.

Have you been fertilizing? Peonies and many other flowering plants will produce more foliage and fewer flowers if they are overfertilized.

But the most likely problem – since your plants are healthy and in a sunny spot - is that they were planted too deep. The peony buds should be planted 1½ inches below the soil level. If planted much deeper than that – even just 3 or 4 inches deep - they will not flower well. You can lift and replant your bushes in late August or early September. Unfortunately, replanting can also set back their blooming, and you may have to wait yet another year to see blossoms.

Note: The master gardeners' series of free educational programs continues this week with Watering Wisely - A guide to watering trees, grass and plants, keeping everything from drying out or being over-watered. 6-7 p.m. Monday, July 8, at Mt. Royal Library, Thursday, July 11, at West Duluth Library.

Written by U of M Extension Master Gardeners in St. Louis County. Send your questions to features@duluthnews.com.