Author: Emily

Perfect Rows: The Mystery Behind Those Holes on Your Tree

Emily Clark WatersonLeave a comment
A closeup of small circular holes in a line on gray tree bark
Sapsucker damage often appears in straight rows or regular patterns on tree bark. Photo: Miri Talabac, UMD Extension

What’s happening to my tree?

This is a question that we often receive at HGIC through our Ask Extension program. Many clients who write in for help think the holes may be from wood-boring insects, but SURPRISE – they are actually from a type of woodpecker! Who knew they could be so neat and precise? Boring insect holes will appear deeper and more random on the trunk or branches of a tree.

These holes are feeding wells of Yellow-bellied Sapsuckers, a native North American bird in the Picidae woodpecker family. This small forest woodpecker frequents mixed-evergreen and hardwood forests (and home yards) in Canada and the eastern U.S. Most of Maryland is within their wintering range. In spring, they migrate northward (and sometimes to parts of western Maryland) for the summer months.

What are Yellow-bellied Sapsuckers?

Yellow-bellied Sapsuckers are about the size of an American Robin. Despite their name, they don’t really have a yellow underside; it’s more white to creamy yellow-ish. Males have a more prominent red cap and a red throat, while females have a red crown with a white throat. Both sexes have vertical white wing patches along their folded wings, which contrast boldly against black plumage.

A bird with black and white feathers, a red cap and creamy yellow breast. Female sapsucker.
Photo: female (c) John Bruin, iNaturalist,some rights reserved (CC BY-NC)
A bird with black and white wings, white breat, and a red cap and throat. Male sapsucker.
Photo: male (c) scaup, iNaturalist, some rights reserved (CC BY)

The short beaks of these birds help to drill fairly shallow wells to feed on the sweet sap, which in early spring begins to flow into tree canopies. Sugary sap, along with some protein from the occasional insects that get trapped in the oozing sap, helps to give the birds the energy they need for surviving the winter and making it to their summer nesting grounds. According to Cornell Ornithology, later in the season, they may also consume some of the cambium bark of trees. But why the perfect rows? It’s simply more efficient. They move from one shallow hole to the next to keep the sap flowing without damaging the inner structure of the tree.

Welcome to the Sap Diner!

Bark damage on a tree showing many circular holes approximately 1/4 to 1/2 inch in diameter. They look similar to a hole made with a hand drill.
Rows of holes line the trunk of this tree resembling a Connect Four game grid, just waiting for some Sapsuckers to come and play! Photo: Home and Garden Information Center
Bark damage on a tree tunk showing larger flat rectangle pecking marks.
Tree bark resembling your typical waffle. Photo from Ask Extension, Home and Garden Information Center

You may have noticed two different types of patterns on trees, and this has to do with the birds feeding at different times in the season. Some bark damage looks more like the perfect grid of waffles waiting for the sweet syrup to fill the wells, while other damage is the straight holes of a Connect Four game grid. In early spring, the same time we tap Sugar Maples to collect sap for maple syrup making, sapsuckers drill deep holes to reach the sweet sap that is starting to flow in the inner sapwood of the tree. Later in the spring, after the tree produces leaves, the sugar is in the outer part of the trunk, bringing nutrients down to the tree’s roots, allowing the sapsuckers to drill shallower holes to access sap.
Rows of holes line the trunk of this tree resembling a Connect Four game grid, just waiting for some Sapsuckers to come and play! Photo: Home and Garden Information Center

A graphic titled: Tree Stem Basics: Yellow-Bellied Sapsucker Showing a cross-section of a tree trunk depicting bark on the outer ring, next layer: phloem, then cambium. The inner (4) rings are xylem with the center of the trunk (heartwood) showing but not labeled. A Sapsuckers beak on the leftside of the tree is inserted in the xylem layers and this is showing early sping: sap wells drilled into sapwood. A sapsuckers beak on the right side is inserted into the phloem layer and this is in late spring that sap wells are drilled into phloem.
Graphic: Joe Boggs, Ohio State University Extension

Yellow-bellied Sapsuckers are considered a keystone species, meaning without their existence the ecosystem would be vastly different. Those sap taps don’t only feed the sapsuckers, but dozens of other species!

Birds:

  • Hummingbirds: The sap wells are critical sources of food in the early spring for migrating Ruby-throated hummers since many nectar-producing flowers aren’t in bloom yet.
  • Warblers: At least 7 species of these migratory songbirds frequent the sap wells.
  • Woodpeckers: Other woodpecker species use the sap wells and the insects they attract as a food source.
  • Many other songbirds: They visit these backyard feeding stations for a sugary treat as well.
A tree trunk with many circular holes and a hummingbird feeding on 1 side while a Sapsucker feeds on the other side of the trunk.
Ruby-throated Hummingbird (left) and Yellow-bellied Sapsucker (right) sharing sap wells by Pam Campbell; Cornell Lab of Ornithology | Macaulay Library

Mammals:

  • Any of the tree-dwelling mammals: Squirrels, chipmunks, mice, etc., lap up yummy sap.
  • Porcupines: They are known to strip bark off trees, and they also benefit from the ready-made sap source.
  • Bats: Some bat species stop by for the sugar and insects.
A squirrel on the side of a tree seemingly drinks sap from a sap sucker well.
A squirrel investigates the sap wells on a tree. Photo: Home and Garden Information Center

Insects:

  • Butterflies and Moths: The wells are a great food source of nutrient-rich sap.
  • Stinging insects: Bees, wasps, and hornets are often seen buzzing around the holes.
  • Ants, beetles, and flies: They will crawl into the holes and usually become a snack for other visiting birds.

Wait, what about my tree?

So now that you know what those holes are from, should you be worried about your tree? Yes and no. Many studies have shown that yellow-bellied sapsuckers tend to drill on already-stressed trees. This is why we may notice it more in our backyards and parks rather than on a hike in the woods. Even if you diligently care for your holly or maple (or other trees or shrubs), these plants may not be in their natural wooded setting and could be stressed from any number of factors:

  • drought
  • soil compaction from regular lawn mowing or foot traffic
  • lower levels of nutrients in urban/suburban soil (due to fallen leaves and other plant debris usually not being left in place to decompose and return nutrients to the ground)
  • newly-planted specimens and those still getting established
  • increasing heat (especially when temperatures remain warm overnight)
  • insect or disease damage

However, severely-stressed trees also have poor sap flow, so you will likely also see drilling on fairly healthy trees. Sapsuckers prefer species that tend to be higher in sugar (maple, birch, apple) or trees with smooth outer bark (holly, beech, cherry). Younger trees also have less furrowed bark, so those may be more attractive. This doesn’t mean you shouldn’t plant these trees in your yard. They all add wonderful shade, fruit, or winter interest.

The bottom line is that heavy feeding from Yellow-bellied Sapsuckers could harm your young or stressed trees, but they don’t kill all trees. On a healthy tree, the damage may only be cosmetic, and the holes will seal over, unless the tree is entirely girdled. Many holes on a young or vulnerable tree could cause branch dieback, leaf wilting or browning, or further weaken potentially already-stressed trees.

So, what can you do? If the tree is young, you can protect the bark by loosely wrapping it with burlap or hardware cloth. This isn’t practical on large mature trees, though. In that case, its important to keep additional stress to the tree to a minimum.

  • Monitor for watering needs: Even mature trees need about 1 inch of water a week during the growing season when there isn’t sufficient rain. Maryland often goes through periods of high heat and drought, so it’s important to protect our mature trees by irrigating when we can. Don’t forget about the fall, even if the weather is cooling off. This is a critical time to support the roots before the ground freezes.
  • Add mulch: If there isn’t a mulch disc around the root zone, consider applying 2 to 3 inches of a biodegradable mulch, so its nutrients add to the soil as it decomposes. You can use shredded or chipped bark mulch, arborist wood chips, fallen leaves, pine needles, or another organic material. The organic matter that mulch adds discourages soil compaction,  improves soil moisture-holding capacity and moderates soil temperatures, and protects the tree’s trunk from mowing or weed-whacking injuries. Just keep the mulch pulled back a few inches from the tree’s bark and avoid “mulch volcanoes” around the root flare!
  • Add more native plants to your yard or help advocate for native plants in a local park: There may not be a solution to prevent sapsucker feeding, but making sure we have an abundance of food sources for woodpeckers and other wildlife to choose from helps our urban/suburban landscapes recover if and when we do lose a tree. Explore the Maryland Native Plants Program resources to help select plants best-suited to your conditions.

Keep in mind that Yellow-bellied Sapsuckers are protected under the Federal Migratory Bird Treaty Act of 1918. This makes it illegal to kill, capture, or harm them, and as a keystone species, why would we, especially now that we know all they do for our ecosystems?

If you notice neat holes or grid patterns on your trees or shrubs, consider all the wildlife you are helping through that one plant! I’m sure they are all thankful for it.

Sources and additional resources to explore:

UME HGIC: Woodpecker and Sapsucker Damage on Trees

Cornell Lab All About Birds: Yellow-bellied Sapsuckers – This link allows you to listen to the sapsuckers’ various calls.

Georgia Dept. of Natural Resources Wildlife Division: Out My Backdoor: How Sapsuckers Help Hummers

Ohio State University: Buckeye Yard and Garden Online: Rows of Holes on Tree Bark

By Emily Clark Waterson, Certified Professional Horticulturist & Coordinator, Chesapeake Bay Landscape Professional, University of Maryland Extension Home and Garden Information Center

Gardening with Life Changes: a reflection on growing in containers

Emily Clark Waterson2 Comments
Calico cat resting inside a large pot with plants and colorful garden decorations on a balcony
Zelda the cat loves to lounge amongst the plants in the sun, despite the attempted deterrence of forks, chopsticks, and watering bulbs. Photo by: Emily Clark Waterson

I imagine for many gardeners, life changes may also come with garden changes. For instance, maybe you relocate and the sunny plot you once had is now a tree-covered shady oasis. Maybe the time you were able to devote to your garden shifts with the expansion of your family. New babies are a welcome addition, but boy, do they take a lot of time! Believe me, I know! That first week the weeds took over. Your job may change and now you have a longer commute or different work hours. You may decide to introduce a new pet that loves to dig or doesn’t respect that new shrub you are trying to establish. I have experienced many of these changes, which have allowed for a variety of gardening scenarios. Each life change has brought a new gardening challenge to explore and I welcome them all!

How it started…

I started my mid-Atlantic gardening life in 2011 with about 1/3 of an acre in a typical suburban neighborhood. I grew up in Northern New York (mostly zone 3-4) and then spent a few post-college years in the Southwest, so I found it exciting to learn about the planting palette of the Piedmont Region. At the time, I was working at a local garden center. That employee discount was a big bonus! I transformed a lot of turf and compacted construction soil into vibrant garden spaces. They showcased native plants, various edibles, and some fun non-invasive ornamental species. I introduced multiple trees to the barren backyard. I built some raised-bed veggie gardens and I finally found a happy spot for rhubarb to grow, after relocating it about five times. (Rhubarb prefers cooler climates but there are some heat-tolerant varieties if you’re like me and can’t live without it!) I also added the all-important gardener’s gold: a compost pile.

Two 4 by 8 foot raised beds in wooden frames sit along side a fence in a backyard with a path around them lined with bricks.
Newly built raised bed vegetable gardens waiting to be planted. Photo: Emily Clark Waterson
Two toddler aged children sitting on the grass in a backyard holding beets
My forever garden helpers in 2017 with our beet harvest. Photo Emily Clark Waterson
A sunny garden bed with various trees, shrubs, and flowers with a fence in the background and grass in the foreground.
The full sun backyard garden bed was added to soften the corners of what was once a rectangular plot of grass. Photo: Emily Clark Waterson

How it changed…

A recent life change had me relocating to an apartment, resulting in a drastic reduction in my gardening space in 2023. But when life gives you a balcony, you start container gardening! I can’t live without dirt under my nails, or in this case, potting mix. Therefore, the balcony had no choice but to come alive with shades of green! It faced east and also received some shade from a large deciduous Magnolia. This was a change from the full sun, southern-facing backyard I was used to.

I scoured my local thrift stores for plant containers or something that could be repurposed as one. If I could drill a drainage hole, it would be fair game! Fun plates became container saucers to put underneath draining pots so they wouldn’t drip on my downstairs neighbor. Surprisingly, I found self-watering containers for a low cost at a dollar store. To further save money for plants and seeds, I used recycled food containers for seed starting. I optimized space by thinking vertically and splurged on a self-watering railing box. Adding hooks for some hanging plants was a must, too!

I’m a self-proclaimed native plant nerd, so there had to be some natives incorporated. I missed popping out my back door to my herb garden. Being able to clip whatever aromatic additive I wanted for an evening cocktail or our dinner was such a luxury. So, ignoring the eastern-facing orientation, I planted sun-loving Mediterranean herbs in various pots. I love fresh salad greens to harvest in the cut-and-come-again method. With the shadier location, this meant I was able to grow them all summer long in the railing box. Despite the lower light conditions, I tested a spicy pepper and a few cherry tomato plants as well. Guess what? They all grew!

A rectangular plastic container filled with soil with small seedlings emerging, sitting on a railing.
A repurposed food container and lid growing arugula seedlings. Photo: Emily Clark Waterson
Green lettuce plants growing in a black oval planter with soil and wood mulch on a balcony railing.
Having fresh green lettuce growing along the balcony railing was great to snip leaves off and have it grow back. Photo: Emily Clark Waterson
A view of a balcony with many potted plants and a tree in the background
A midsummer view of all the plants in the balcony garden. Photo: Emily Clark Waterson
Tomato plant reaching over a balcony railing to the roof line, held up with twine.
Due to the lower light conditions, the tomatoes grew a little spindly, but still produced. Photo: Emily Clark Waterson
A hand holding 3 red cherry tomatoes with a tomato plant in the background displaying many green tomatoes.
Tomato harvest with more on the way! Photo: Emily Clark Waterson

Challenges

Every gardener knows there is always something to learn from. Here are some challenges I faced:

Every gardener knows there is always something to learn from. Here are a couple of challenges I faced:

  • Cats – We love our cute kitties, who we rescued from a sewer drain at 4 weeks old, but cats and potted plants are a tough combination. Living in 900 square feet, it was important stimulation for them to explore the balcony and get some outside time in a safe setting where they couldn’t hunt wildlife or get hurt. Link liked to eat radish tops, and Zelda nibbled all the Carex (sedge) in my native plant container. (Yes, Link and Zelda – named by my 2 pre-teen boys who like to play video games.) Any open soil became a convenient litter box, so I learned to keep it blocked or covered. Chopsticks from the occasional takeout became repurposed soil blocking stakes. Any container not large enough or heavy enough had the potential to get knocked over (and many did). We learned to live with the nibbling, and I grew lots of wheat grass for them to keep them from eating MY plants. It didn’t totally work, though.
  • Heat and watering: Containers dry out much quicker than soil in the ground. I used many watering bulbs or those terra cotta watering spikes with bottles to help keep plants watered on the hottest days of the summer. If you have access to a hose bib, you can invest in a small drip irrigation system set on a timer, which would be more regulated for water hogs like tomatoes.
  • Plant waste: Where does it go to decompose? I didn’t want to add more waste to the garbage bags we had to haul out to the dumpster, and for environmental purposes, composting is preferred. I ended up using a 5-gallon bucket to collect spent potting mix, leaf clippings, and deadheaded flowers. On occasion, I added old potatoes, moldy fruit, or veggie scraps to balance the greens and browns. They slowly broke down, and if it didn’t get reused, at least it was easier to carry down 3 flights of stairs. My city had a compost collection service that you can sign up for, but unfortunately, they didn’t pick up from the apartment complex.

How it’s going…

Another life change has now brought me back to a yard. Since we are renting for now, I will continue container gardening, but with much more space! [Insert grow bags!] And just in time for our Grow it Eat it Year of Container Gardening! I’m excited about what this growing season will bring!

Thus far, I have overwintered spinach from the balcony garden; how it survived multiple freezes and probably fully frozen potting media, I have no idea, but that’s why plants are so cool! We’ve planted arugula and some mixed salad green seeds that are starting to show signs of life, peas that can climb our porch railing, and plenty of culinary herb transplants from the local garden center. I needed something instant to harvest!

A container sitting on porch steps showing a small Thai basil plant in the back and basil seedlings in the front.
Thai basil transplant and basil seedlings are popping up. April 18, 2026 Photo: Emily Clark Waterson
Herbs in a container with a road in the background.
The sage overwintered but we just added thyme and oregano. Chive seeds were planted in the empty space. April 18, 2026 Photo: Emily Clark Waterson
Overwintered spinach made the move with us and is reviving its growth in the railing box. Arugula seedlings are just starting to come up as well. Date: April 18, 2026 Photo: Emily Clark Waterson

We have a bit more sun now, and the kitties are confined to their screened-in “catio”, so some challenges have been addressed. My native plant container that Zelda liked to lounge in succumbed to heat and lack of watering while on vacation and then the freezing temperatures over the first winter, so I replanted with more drought-tolerant native shade perennials late last fall. Happy to report that they all survived and are returning vigorously! I’ve added a container variety of thornless raspberry, Bushel and Berry® Raspberry Shortcake®, to experiment with and excite our kids. Tomatoes, carrots, Thai peppers, and container-sized cucumber varieties are to come! We’ll see what our yields will bring and what interesting native plants I can add to aid in pollination and beneficial insect populations. Now, to just keep the cats from eating the house plants….

A container with various green plants in different textures with a white picket fence in the background.
The re-planted native plant container features: Zigzag Goldenrod, Appalachian Sedge, Woodland Stonecrop, Christmas Fern, Alumroot, and a hidden Common Blue Violet. Photo: Emily Clark Waterson
A close up of flowers on sedge blades with a ceramic green bird in the background.
The Appalachian Sedge in bloom! You can see the violet blooming in the background. Photo: Emily Clark Waterson
3 containers with different young shrubs inm a corner of a yard against a white picket fence.
The new Raspberry Shortcake in the white container (right) and young native woody plants: Red chokeberry (center), and saplings of Spicebush and Redbud (left). Photo: Emily Clark Waterson

Takeaways:

  • Just because you don’t have a plot of land doesn’t mean you can’t grow something!
  • Lack of full sun does not equal zero veggies – I had that cherry tomato producing well into late October!
  • Challenges provide good, thought-provoking scenarios that keep you interested in growing! Don’t give up if a few plants die.
  • Cost doesn’t have to be a deterrent either – a gallon milk jug with drainage holes and the top cut off worked great for leafy greens.
A wicker basket with many red, orange, and green tomatoes, and 2 purple peppers.
The last harvest from the balcony on November 10, 2025! Photo: Emily Clark Waterson
An apartment building showing 2 balconies with a finger poiting to the top floor. Plants can be seen growing and trailing over the edge.
Our balcony was on the 3rd floor. The vine is a stowaway Creeping Cucumber that must have traveled with another potted plant and ended up growing down to the 2nd-story balcony! Photo Emily Clark Waterson

Wherever life takes me next, I know my garden will follow. We’ll continue to grow and adapt to our new environment, and no matter what, harvest something we can eat!

Happy Spring!

Additional Resources:

By Emily Clark Waterson, Certified Professional Horticulturist & Coordinator, University of Maryland Extension Home and Garden Information Center.