Spring approacheth here in New Hampshire, though in spurts. Today the high was 56F, and very windy, and tomorrow and Friday we’re looking at a forecast of 12 or more inches of snow, with a high temp of 20F on Friday and a low of 1F on Sunday. So — not yet.
In years past, I might have been getting prepared to “clean up” my garden, which would have entailed raking leaves left on the ground in the fall, cleaning up “brush,” cutting back perennials and grasses. But now there’s a wider awareness that while some insects like the monarch butterfly migrate, many beneficial insects overwinter right here in the messiness that we call brush, i.e., leaves, stems cut and left standing, cut stalks, mulch, etc.
Helping insects and other arthropods survive also helps birds survive — once their young are born in the spring, 96% of birds, even most of those who are normally berry and seed eaters, feed their young insects, including many caterpillars. A single pair of breeding chickadees has to find more than 6,000 caterpillars, in a fairly small area around the nest, to raise one clutch.
(Yes, it’s true that slugs, snails, weeds, ash borers, ticks, and pathogens also overwinter in leaves and brush. It’s not a perfect system, but we can address those problems, if they become problems, in an environmentally appropriate way. A common permaculture catch-phrase is “You don’t have a slug problem; you have a duck deficiency.” Which doesn’t mean you necessarily need ducks if you have slugs, though they’re pretty appealing in some ways. It means we can think creatively about what our fundamental situation is, which helps us think about how to move forward.)
Many of these overwintering insects, whether in adult, pupae, larval, or egg form, are very easy to overlook — we don’t notice them — they’re hard to find even if you go looking for them — and we don’t think about them and their life cycles and how they depend on a certain amount of debris, brush, and non-intervention from well-meaning humans.
Some, like the mourning cloak butterfly (Nymphalis antiopa) as well as Eastern Commas, Question Marks, and Milbert’s Tortoiseshells, overwinter as adults camoflauged in leaves and in tree bark, and many butterfly and moth species overwinter as dried-leaf-looking chrysalises and cocoons on standing plants, including swallowtails (Papilio species), sulphurs (Colias species), elfins (Callophrys species), skippers (Hesperiidae), luna moth (Actias luna), and cecropia moth (Hyalophora cecropia). Wild bees usually overwinter as pupae underground or in cavities such as hollow plant stems or holes in wood bored by beetles, and adult queen bumblebees spend the season underground in rodent holes with an insulating layer of leaves over them. Hummingbird clearwing moths and soldier beetles also spend the winter in burrows in the soil. Young spiders often overwinter in egg cases hidden in log piles or under ledges (or in our houses). Wooly bear caterpillars and adult ladybugs, assassin bugs, and damsel bugs overwinter in leaf litter, and if you look under rocks and logs, flower pots, and birdbaths, you’ll probably find someone waiting for spring, hoping you don’t destroy their hiding place.
So, what does one do in the garden in the spring to tidy up? And when does one do it so as not to bother the sleeping creatures?
If you want a rule of thumb as to when — or an urban legend, as Doug Tallamy, whom we’ll get to later, brands it — you can begin to move leaves and brush and start cutting things back after three consecutive days of temperatures over 50F (some say 55F, or 59F); or after seven consecutive days with these temps, if you listen to others. Some suggest waiting until “late spring,” which strikes me as unassailably vague. Or, if you have great eyesight and a lot of time, you can watch each plant/stem/leaf pile to see who’s flown or crawled and who hasn’t emerged before you cut or move anything. Or you can take advice from Tallamy and his ilk and not remove anything at all — not leaves, stems, stalks, nada.
Jessica Walliser, in her March 2016 article “Spring Clean Up Done Right,” (at Savvy Gardening), discusses hollow plant stems that we hopefully remembered to cut to between 8-24 inches high in the fall so that little bugs could spend the winter in them:
“Lots of beneficial insects, including pollinators like tiny native bees and pest-munching predators like syrphid flies, lacewings, and parasitic wasps, spend the winter hunkered down in hollow plant stems either as adults or pupae. Cutting down the dead plant stems too early in the spring will disturb them before they have a chance to emerge. Wait as long as you can to do your spring garden clean up.”
But realising that gardeners prefer to cut down old plant stems before new growth starts she offers an alternative to delaying spring garden clean up:
- Toss cut perennial and woody plant stems onto the compost pile very, very loosely, or spread them out at the edge of the woods. Many of the insects taking shelter inside the plant stems will still be able to emerge when the time is right. When you cut off the plants, leave about 8 inches of stubble behind. These hollow stems will serve as overwintering sites for future generations of insects and the new growth will soon hide them.
- Another option (and the one I prefer) is to take the cut stems and gather them into small bundles of a few dozen stems each. Tie the bundles together with a piece of jute twine and hang them on a fence or lean them against a tree on an angle. Again, the insects sheltering inside of them will emerge when they’re ready. An added bonus of this method: More insects, especially native bees, will move in to the stems and possibly use them as brood chambers all summer long.
If you’re thinking of going the 3-7 consecutive days at between 50-60F route, be aware that the timeframe for those dates will vary widely from year to year. I looked a historical weather records for my town from 2018 to 2021, specifically at the extremes of the recommended times and temps, so three days of 50F (very early spring — iffy) and 7 days of 55F and 60F (quite late in the spring but less iffy); notice the variability of the gaps between the timeframes:
- In 2021, three consecutive days over 50F occured on 22 March; seven consecutive days above 55F on 26 March; and seven in a row over 60F on 27 March! Very early.
- In 2020, three consecutive days over 50F occured on 10 March; seven consecutive days above 55F on 19 May; and seven in a row over 60F on 20 May — almost two months later than in 2020.
- in 2019, three consecutive days over 50F occured on 15 April (those three were over 60F, too); seven consecutive days over 55F on 25 April; and seven in a row over 60F on 22 May.
- in 2018, three consecutive days over 50F occured on 1 March; seven consecutive days over 55F on 27 April; and seven in a row over 60F on 8 May (including a 90F day).
Native plant guru Doug Tallamy, whom I mentioned earlier, recommends in his blog post Leaf Litter: Love It and Leave It (30 March 2021) that we leave leaves forever and resist doing any spring cleanup, so as not to disturb anyone sleeping therein.
“Insects do become active based on a combination of day length and accumulated degree days. That is, there must be a certain number of days above a given temperature for the insect to complete its development within its chrysalis or pupa so it can emerge as an adult. There are also a number of species that overwinter as adults, as larvae, or as eggs whose activity is triggered by warm temperatures and lengthening days. The problem is that each insect species requires its own species-specific temperatures to become active and one prediction of some number of days above 50 does not fit all insects. Species of moths, butterflies, bees, beetles, etc. emerge all season long; some in the spring, others in the summer and others still in the fall. For example, at our house in southeast Pennsylvania, beautiful luna moths and Io moths do not emerge from their cocoons nestled within leaf litter until mid-May; various species of oak leaf-miners don’t emerge as adults until mid-July, and the velvet-bean moth doesn’t appear until the end of August at the earliest. “
August, hmm? Uh-oh.
My plan, and what I’ve done before, is to wait until we have at least seven consecutive days of 55F, which is usually at least mid-April here, and then be careful when cutting, placing stems and stalks that aren’t diseased in a loose bin (not really a compost bin) open to the air. I remove leaves (to the same open-air bin) carefully if they are suppressing plants or grass, but often it’s not necessary. I keep an eye out when pruning trees, shrubs, and woody perennials for any cocoons or chrysalises, leaving the branches they’re on for later. I’m sure I miss some overwinterers but I think I disturb many fewer than I used to.
You don’t have to clean up everything or even most things. Leaving the stems you cut back to 12-15″ (or 8-24″ per some advice) in the fall is fine in most places in the garden; soon those stems won’t be visible anymore as plants grow. Heather Holm, wild bee queen, talks about this and lots of other things with Margaret Roach at a Way to Garden — Bee Friendly Garden Cleanup, Nov. 2020
Xerces’ Nesting and Overwintering Habitat pdf (12 pp) is excellent (with photos!). It suggests waiting until “late spring” to remove leaves and such on the ground (and also suggests not cutting back the stems you left in the fall).
The Corner Pollinator Garden & Wildlife Habitat’s post “Pollinator Garden Spring Clean-Up” is full of great tips.
How to Help Bees and Butterflies Survive the Winter, Univ. of NH Extension, 23 Oct. 2019.
What to do With Fallen Leaves by David Mizejewski, National Wildlife Federation, 1 Sept. 2021.
Featured image is a rusty tussock moth egg case, 3 April 2012, which I found while cleaning up the garden