Are all hydrangeas perennials? If not, how can you tell which are or which are not?

All hydrangeas are either woody or herbaceous perennials. The problem for northern states like Michigan is that not all hydrangeas are winter hardy, and are not able to take the Zone 5 winters that can dip to -20 degrees. We seem to crave those bigleaf hydrangeas (Hydrangea macrophylla) with lovely pink and blue, large lacecaps. They do not do well in Zone 5 unless extremely well-sited. Once you travel south into Zone 6 and beyond, the plants become more common and successful. In Zone 5, these hydrangeas should be considered container plants to be brought inside for the winter.

There is a climbing hydrangea (H. petiolaris), which is winter hardy here and can be used both as a shrub or a disguise for a large structure. It produces a white blossom in late June that is fragrant and lasts for two weeks or more. Two other hydrangeas with a large shrub or spreading tree habit are panicle hydrangea (H. paniculata) and oakleaf hydrangea (H. quercifolia). Both are winter hardy and work well in a larger landscape. In both cases, it is important to obtain a named variety from a reputable nursery to insure plant characteristics live up to your expectations.

We get dead circles in our grass. Inside the circle, the grass looks fine. We have had the grass replaced, aerated, and seeded, yet the problem keeps returning. How do we fix this?

The symptoms you describe are characteristic of yellow patch (caused by a Rhizoctonia fungus), sometimes known as “frog eye” or “summer patch.” It occurs during hot, dry and windy weather near the end of summer. Drought-stressed, shallow-rooted Kentucky bluegrass lawns are the most susceptible. It often shows up near paving or parts of the lawn that dry out first.

You need to review your lawn maintenance and cultural practices. Overuse of nitrogen fertilizers and excess thatch can make the problem worse. By aerating, you have taken a step to reduce thatch and improve water penetration. Make very sure that your mower blades are sharp, and that the grass is mowed no shorter than 2-1/2 inches. Mowing too short sets the lawn up for weeds and further disease. When you water, water deeply to wet the entire root zone and water consistently. Do not let the turf dry out. Betting on Mother Nature to be cooperative with her rain showers can often make the homeowner the loser in the “turf stakes.” Apply less nitrogen, particularly in midsummer, on Kentucky bluegrass lawns.

If you find you must reseed, select resistant varieties. Studies have also shown that simply adding a small percentage of perennial ryegrass to bluegrass can greatly reduce the problem.

We are able to get free ash tree chips from local landscapers. Most of the chips are less than 1 inch, but there are occasionally large wood chunks. Are these chips safe to use? Will we be bringing the emerald ash borer (EAB) into our yard? We do not have any ash trees, but can these insects cause harm to other plants?

Using the chips is not likely to introduce the ash borer, but it is possible. When Genesee County was outside of the EAB quarantine zone, some trees became infested near the processing plant that was burning the ash chips.

If you live outside of the quarantine zone (note that virtually all of southeastern Michigan is in the quarantine zone), do not bring in ash chips on the small chance of accidental infestation. If you live within the quarantine zone, feel free to use the chips.

So far there has been no known instances of the EAB infesting any plants other than ash trees.