Q: I’ve heard that not all of our praying mantis types are native. They’re all good for garden pest control though, right, or are some bad instead?
A: Maryland is currently home to five species of praying mantis, but only one is native, which is the Carolina mantis. The others are the European, Chinese, narrow-winged and Asian jumping mantids, with the latter being the most recent introduction. While non-native, the other mantids have more-or-less been integrated into our ecosystem for some time now, so they don’t necessarily need management or removal. Evidence of this includes the fact that insect-eating birds and other predators will readily consume them, and their eggs can also be parasitized by the tiny wasps that presumably evolved to have a relationship with our native mantis. In the grand scheme of things, other invasive species deserve more attention. Plus, at least they also eat various other non-native insect pests.
If you prefer to support native mantids found in your yard, make sure you’ve identified them correctly. Maryland Biodiversity Project has image galleries for each mantis species and provides a few ID tips for telling the difference between them, at least for adults and egg cases (called ootheca). Put “mantids” in the search box to see the species list.
Mantids are generalist predators, so can consume pest insects and beneficials like pollinators alike. They’re opportunists, nabbing anything they can subdue (including each other), so are neither universally good nor bad. Gardeners generally consider them helpers since they do consume pests, though we don’t know to what extent the non-native species may be depriving the native species of a food source due to competition. (Given how many other non-native insects exist in our area, I imagine this impact isn’t that significant, especially when compared to the greater problem of habitat loss and degradation.)
Q: When do I trim spirea? Like hydrangeas, I find this group confusing because I keep finding different answers to that question.
A: Aha, this is because they have the same duality as hydrangeas do — as a group, they can either be new-wood flowering or old-wood flowering, depending on the species. This simply means that it’s either the older growth (stem wood produced the year before) or newest growth (stem wood produced the current year) that forms flowers. Since the timing of this growth differs, that means the timing of pruning needs to be different as well so you don’t remove flower buds.
Shrubs like bumald and Japanese spirea (spiraea x bumalda and S. japonica, respectively) flower on new wood, so in winter there are no flower buds present because they will be forming on growth made later that summer. These can be cut back as desired in late winter without loss of bloom. The majority of commonly-grown cultivars belong to this group.
Spring-blooming species like thunberg spirea (S. thunbergii), Bridalwreath (S. prunifolia), and the assorted similar, bridalwreath-esque species like nippon (S. nipponica), reeves (S. cantoniensis), and vanhoutte (S. x vanhouttei) spirea cultivars all bloom on old wood in early to mid-spring. If trimmed in autumn or winter, those buds will be sacrificed and won’t regrow until the summer (to open the following spring). The health of the shrub won’t be impacted if you get the timing wrong, it just won’t bloom that year. Instead, trim varieties in this group as needed just after the flowers fade.
I encourage Maryland gardeners to try our native spireas (S. alba and/or latifolia, plus S. tomentosa), especially if you have a meadow type of natural area or mid-size perennials they can mingle with in a garden bed. Picture astilbe-ish flower clusters in white or pink on a relatively slender upright shrub. They both bloom on new growth, which allows you to do your annual meadow mowing while still allowing the shrubs to bloom later in the summer.
University of Maryland Extension’s Home and Garden Information Center offers free gardening and pest information at extension.umd.edu/hgic. Click “Ask Extension” to send questions and photos.