August 15, 2012

Heads Up!: Chinese Elm Summer Limb Drop

The first time we saw our property before buying it, we pulled into the cul-de-sac, walked straight through the 960 sq. ft. home as others chatted with the realtor, and stepped into the backyard. One look at the mature shade trees and the huge blank slate of a yard and we said, "This is the place!" It's been ten years and we've thoroughly enjoyed those beautiful trees, the shade they provide, the leaves they add to the compost pile, and the birds they attract to the homestead.

Unfortunately, large, mature trees also mean lots of mess, lots of maintenance, and the occasional hassle of, and sometimes damage from, a large limb dropping off a tree. This often happens in the middle of a wet, windy, January storm, but other times it happens out of the blue on a still, hot summer afternoon, as it did yesterday.

Chinese Elm branch on top of a tomato patch

There was about half an hour of daylight left yesterday evening when we heard a very loud, fast scraping sound on the roof followed by a huge thunk and vibration of the ground. One look out the bedroom window confirmed what we suspected--a huge branch had dropped off our very tall Chinese elm tree. This is not the first time we've lost a branch from the elm, but it's the first time I can remember this particular tree losing one under these circumstances.

4-5 inch diameter Chinese Elm branch in the patio

There's actually a name for the phenomenon of trees randomly dropping branches on calm, warm days between May and October: it's called summer limb drop (also known as summer branch drop or sudden limb drop). Arborists have all kinds of theories about what causes it, but there isn't consensus.

Many tree people believe it's caused by an uptake of large amounts of water in an attempt to keep the tree hydrated during a heat spell, followed by an inability to get rid of that water quickly enough, causing internal cell failure and then branch breakage. Whatever the cause, it's impossible to predict. Some trees--such as elms, oaks, eucalyptus, and Bradford pears--are more prone to summer limb drop. Our black walnut has unexpectedly shed several big limbs in the summer months over the last ten years, which is always alarming due to its location over the back lawn, garden and play area.

In this case, we called in an arborist to confirm the diagnosis, and the assessment was as expected--our Chinese elm is a lovely, strong tree and we just have to expect the occasional branch to break off this time of year. We were reassured that summer limb drop typically happens with smaller branches, not the very large main branches that could otherwise do serious damage to a house.

Chinese Elm shading the house

Large or extra large branch, we're simply thankful that nobody was hurt yesterday (unless you count the five flattened tomato plants and cages.) The kids play in the yard constantly this time of year, so the idea that it's normal to randomly lose what I consider to be pretty big branches off our backyard trees on a calm summer day is more than a bit scary, but I suppose it's the price we pay to maintain an urban forest.

We've considered removing the tree entirely and replacing it with a slightly smaller variety that's not prone to limb drop, but the elm is a healthy tree that's responsible for a fair amount of energy savings in the summer and it would take years for another tree to grow tall enough to shade the house. What would you do? Live with the chance that another big branch will drop and possibly hurt someone, or take out a mature tree that is providing all kinds of benefits on the homestead?


  1. Leave your Chinese Elm where it is. They are lovely when mature and I just had a summer limb drop off our 80 year old Elm today. It's heart breaking with the California drought in it's 4th year as we NEED the shade on that side of our house (southwest). Plus I just love full green trees more than anything else in our yard. We had it trimmed last year and tree guy did an uneven job so maybe the limb falling in the still of summer had something to do with that. Hope you kept your Chinese Elm....they are one of my favorite trees.

    1. Yes, we did keep our Chinese Elm. We rely on ours to shade our house, too. It's been happily filling the front patio with leaves all summer, and hasn't dropped a limb since I wrote this post four years ago.

  2. I'm glad I found your post! We just had about a 4" diameter limb drop on our Chinese Elm. We've had an unusually wet Texas summer. Your explanation saved me a call! Thank you.

    1. Glad you found the information helpful!