When to prune hydrangeas
Q: I have a hydrangea shrub that may need pruning, but how can I tell when to trim?
A: Pruning a hydrangea is largely an optional exercise, in that plants don’t require routine trimming to be healthy. If your shrub isn’t too large for the space, you don’t necessarily have to trim it. Timing depends on the hydrangea species, at least if you want to avoid forfeiting blooms that season. For the most part, hydrangea species are relatively easy to tell apart, at least during the growing season, if you need to identify the type first.
Hydrangeas are grouped into two categories based on when they bloom. Those that will be producing flowers on the growth of the current year are termed “new-wood” bloomers. Those that produce flowers on the previous year’s growth are “old-wood” bloomers. Few in the old-wood group can replace buds lost for any reason (trimming, deer browsing, or cold damage).
New-wood bloomers can be trimmed now (late winter/early spring). While not required for a good bloom, it might lessen summer flopping. Smooth hydrangea (hydrangea arborescens) and panicle hydrangea (H. paniculata) fall into this category.
The pruning of old-wood bloomers should wait until the flowers are fading or just spent, the timing of which will depend on the species but is generally in summer. Bigleaf Hydrangea (H. macrophylla) and its close cousin mountain hydrangea (H. serrata), along with oakleaf hydrangea (H. quercifolia), are in this category. Their flower buds lie dormant on the bare stems all winter, so if trimmed before bloom, they’re removed for good that year.
The only exception would be select cultivars of bigleaf and mountain hydrangea that are capable of reblooming, a trait termed “remontant.” When these are trimmed too early, the buds on old wood are still sacrificed, but the plant can flower on new wood later in the season. The past decade or two has seen many remontant varieties introduced to the market.
You can apply this pruning approach to most other flowering shrubs as well — spring-flowering shrubs bloom on old wood and are best pruned just after flowering, and summer-flowering shrubs bloom on new wood and can be pruned in early spring since their flower buds haven’t yet developed.
Q: Japanese stiltgrass is the bane of my lawn’s existence. What can I do this year to keep it at bay? A:
This invasive weed germinates two to three weeks earlier than another common grassy summer lawn scourge, crabgrass. That means control efforts need to begin sooner — right about now, in fact, or in the next few weeks for central and southern MD.
A pre-emergent herbicide targeted to grassy weeds is the simplest approach, though certain formulations are not permitted by some jurisdictions. These prevent germination of seeds, so if applied too late (after germination), they will not be effective. Pre-emergent
herbicides function by creating a chemical barrier to the emerging weed roots in the surface layer of soil. Desirable plants and established weeds already have roots safely below this layer. If the soil surface is disturbed by digging or aerating, the barrier will be broken and give seeds an opportunity to establish. Therefore, skip applications on any areas you intend to dig or renovate.
As with all pesticides, carefully read the product’s instructions since formulations vary. Most will not allow for turf reseeding the same season because there won’t be enough time for the herbicide to degrade before the seeding window closes. (Turf seeding is best done in autumn anyway, given the option.) Additionally, some products may provide the best control when applied twice over the course of the spring season, separated by several weeks. See what the label allows.
Pesticide-free options are
limited to physical removal as stiltgrass appears, plus preventive efforts that rely on keeping the soil covered and undisturbed so seeds are less likely to germinate. This physical barrier can be ground-covering plants or an organic mulch. Full-on smothering, however, is not feasible with a lawn unless you need to completely renovate a weed-infested area. You can essentially smother weed seeds with healthy turf, though. This entails maintaining a dense, vigorous lawn with practices you’ve likely heard us recommend before: using high-quality seed of disease-resistant varieties, overseeding annually to keep growth dense, minimizing soil compaction, mowing high, and using soil test results to direct fertilization or pH adjustment.
Ideally, any problem areas where the lawn routinely succumbs to weed invasion should be replanted with lawn
alternatives instead of continuing to fight the inevitable. There are several aggressive native plants that might keep stiltgrass from reinvading an area, but they will be less successful if the existing population isn’t reduced before planting.
Stiltgrass seeds can remain viable in the soil for years, so at the very least, until you can get a colony under control, keep it from going to seed in late summer and early autumn. Although not a singular solution, deer can bring seeds into a yard on their fur, so if you can exclude deer from passing through, that may also help to reduce its recurrence. You can learn more on our web page titled “Japanese Stiltgrass.”