Leaving the Leaves—Is It Really Beneficial?

Photo: Xerces Society Leave the Leaves sign.

Compiled by Ruth Gonzalez for Reems Creek Nursery based on a Xerces Society interview with Dr. Max Ferlauto

https://reemscreek.com/leaving-the-leaves-is-it-really-beneficial/

The short answer is YES.

We’ve heard the term “Leave the Leaves” for a few years now – but what does that mean and why? An astonishing number of insects are nurtured in just one square meter of leaves.

Dr. Ferlauto conducted a study across 20 yards in suburban Maryland – where half the yards kept their leaves and the other half removed their leaves. Then they set up insect emergence traps from April through July to measure how many insects emerged in the various yards. They discovered that insects were still emerging in July and the number of emerging insects they collected in the yards where the leaves were retained is astounding.

How many? 18,000 in one square meter! That’s a shocking number and it forces you to take a second look at the concept of “Leaving your Leaves”.

In the study – what kind of insects did they find in ONE SQUARE METER where they retained the leaves?

• 20 butterflies & moths

• 300 parasitic wasps (generally beneficial insects)

• Over 100 spiders

• Over 300 beetles

• Thousands of flies

In the study – When you remove leaves you reduce insect populations:

• Butterfly and moth emergence reduced by 45%

• Spider population reduced by 56%

• Beetle population reduced by 25%

It is a complex issue with options for everyone. Dr. Ferlauto suggested that every square meter where the leaves are left will have a positive impact on insect populations.

The best case scenario is to leave the leaves where they fall – especially under trees. Next best is to move the leaves to another area of your yard. Leaves can smother grass, so this is a consideration for most of us with lawns. Shredding/mowing is not a good option because insects die in the process. Leaves placed near your vegetable garden will host parasitic wasps who will help protect your vegetables.

Here is an example: The luna moth makes its cocoon in the leaf of a sweetgum tree. That leaf falls to the ground, and the cocoon overwinters in the leaf layer – which provides a soft landing and winter shelter for the cocoon. [Bee City USA-Asheville Note: Luna moths are wonderful insects, but the adult does not have functioning mouth parts and therefore does not nectar on flowers or pollinate them. The adults only live a few days, long enough to reproduce.]

Other tidbits:

• A shallow layer of leaves – no more than 6” high – is best for insects.

• Most insects can’t complete their life cycle in a compost pile – it is too deep and maybe too hot.

• Soil carbon accumulates where leaves are left – which positively impacts climate change.

Challenge: Can you dedicate just one square meter of your yard to “leaving the leaves”? All our yards together add up to turning the tide.

*This article is a synopsis of a Xerces society interview with Dr. Max Ferlauto, state entomologist with the Maryland Department of Natural Resources, on Bug Banter with the Xerces Society. Link to the full interview: https://xerces.org/bug-banter/leave-leaves-or-lose-insects

The Leave the Leaves sign pictured above is available through the Xerces Society.