The Q&A Archives: Diabolo Ninebark Has Not Bloomed, No Buds Either, In Zone 7

Question: I purchased and planted a Monrovia Diabolo Ninebark this spring. It is in full sun. It is now August and it did not bloom at all. Should it have this season since it was just planted? What should I feed it with and/or how should I prune it to have it flower next year.

Answer: Physocarpus opulifolius 'Monlo' or "Diabolo" normally blooms in late spring to early summer. If pruning is necessary it can be done immediately after it blooms, or it can be done in winter although this will remove some of the coming year's flowering wood.

This is a rather large plant, and it is best pruned by removing some of the oldest stems at the base every year. This allows the natural form of the plant to develop. This also thins the plant to allow air and light to penetrate and encourages vigorous new growth from the base on an ongoing basis. This type of regular pruning would be started after the plant has been in place for a few years and become quite dense.

I suspect your plant either bloomed before you received it, or was trimmed back hard early in the season to stimulate bushiness. You should have blooms next summer as long as you are not pruning it incorrectly.

This is a sturdy plant and should not require much extra feeding assuming your soil is of average or better quality. If desired, give it a topdressing of compost and/or a complete fertilizer such as 10-10-10 in granular form in early spring according to the label instructions. It is better to underfertilize than overfeed in any case.

With a new plant, the best things you can do are apply a layer of organic mulch several inches thick over the root zone but not touching the stems, and maintain soil moisture.

Your goal in watering is to keep the soil evenly moist but not sopping wet. An occasional deep watering is better than a daily light sprinkling. Sometimes the potting mix and native soil dry out at different rates. It is a good idea to water, wait a few hours, then come back and dig down into the soil to see how effective you watering really was. (It can be surprising.) You would also want to use your finger to dig down and check and see if and when you need to water again to supplement natural rain. Make sure the soil is moist through the fall, up until the ground freezes.

As with most plants, it can take several years for a new shrub to really settle in and perform its best. Enjoy your ninebark!

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