Q: Here's a photo of plants I've found in two different flower beds around our yard. They're pretty, but look weed-like also. Are they a friend or foe? — Kathy Greener, Fargo.
A: Pull the plants as fast as you can. They're weeds, very bad weeds, with the unusual names flower-of-an-hour, Venice mallow or shoo-fly. The botanical name is Hibiscus trionum. Although you can purchase the seed as a wildflower, it's really a weed in sheep's clothing, and is considered a noxious or invasive species in much of the United States.
A weed is defined as "any plant out of place," and this wildflower quickly becomes out of place. Flower-of-an-hour is an annual that seeds very heavily, and quickly becomes entrenched. I can vouch for its nastiness. Its one redeeming quality is the ease with which it pulls, as it doesn't root deeply.
Q: Is Bloomstruck Hydrangea a new, more hardy variety of Endless Summer Hydrangea? I agree with your assessment of Endless Summer not adapted in this area, as I've tried them twice in past years without good results. I was hoping Bloomstruck was an improvement. — Lenore Grande, Moorhead.
A: Your unsuccessful experience with Endless Summer is similar to the majority of those who have tried it in North Dakota and large parts of Minnesota. The basic problem is that the Endless Summer group of hydrangeas, including Bloomstruck, are members of the Hydrangea macrophylla species, which is the species of the non-adapted florist hydrangeas.
The two hydrangea species that are best-adapted for our outdoor landscapes are Hydrangea paniculata and Hydrangea arborescens and their cultivars. Checking the fine print on hydrangea labels for the species saves much heartache.
Because Bloomstruck is a Hydrangea macrophylla variety, it has a disadvantage in our region from the onset because of its genetics. Bloomstruck is fairly new, so time will tell, but it would be surprising if it performs better than its genetics allow.
Q: Is it okay to prune the top of our arborvitae so that it doesn't grow too tall? Its width is fine, but the top is at about 8 feet and we'd like it to stay at that height. — Nancy Suttle, West Fargo.
A: Yes, the tops of pyramidal arborvitae can be trimmed so they don't become too tall. If an arborvitae is allowed to grow out of bounds, it's difficult to radically reduce its height back down to desired size. Your idea of maintaining it at 8 feet from the start is much better than someday trying to cut a tall arborvitae back down to that level.
Keeping a shrub or tree at its present size through pruning is often called "mold and hold" pruning. Several times during the growing season, prune off the current season's new growth so the arborvitae remains at the desired height. Some pyramidal arborvitae varieties' natural heights are 30 feet, so diligence may be needed to maintain at 8 feet.
To hold an arborvitae at its present size, it's probably necessary to trim once in June or July and again in August. A quick trim across the top a couple times each summer should do it.