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Big City, Big Trees
Tree Bed Care
Give a Tree a Chance!
Urban trees have it hard. They must endure drought, lack of growing space, and infertile, compacted soil. People pile trash around them, slam car doors into them, and let their pets use them as litter boxes.
But trees do so much to improve our lives, from cleaning the air we breathe to giving city dwellers contact with the natural world. Paying attention to tree beds—those small sidewalk openings for street trees—can do wonders for the health of street trees and the beauty of your block.
Here are some ways to give a street tree a fighting chance.
1. Give Tree Beds a Spring Tune-Up
The soil in an average tree bed is in poor condition—compacted, infertile, tainted with road salt, and often very alkaline.
Follow these steps to improve the soil:
- Salt used to de-ice sidewalks can severely damage trees—use sand instead. In spring, flush the tree bed with lots of water to help remove salt deposits from the soil.
- Mix in a thin layer of compost annually (maximum: 1/2 inch in depth).
- Use a hand cultivator (a tool that looks like a three-pronged claw) to loosen and aerate the top 1 to 2 inches of soil. The majority of a tree's roots are in the top 18 inches of soil, so be gentle!
- Add a 2- to 3-inch layer of mulch, being careful not to pile it against the tree's trunk. Mulch smothers weeds, helps retain moisture, and makes good compost when it decomposes. Replenish the mulch as it breaks down, and replace all of it each spring or if it becomes tainted with trash or animal waste.
2. Water
The area of exposed soil in a tree bed is relatively small, so even without a drought, a street tree is at a great disadvantage for receiving and retaining its full requirement of water. You can help by watering newly planted trees with about 10 to 15 gallons of water a week. Mature trees benefit from receiving 8 to 10 gallons of water a week during the hot season or periods without rain. The key is to water slowly: Set a hose to trickle water into the bed for an hour; or prick a few holes on one side of a clean garbage can, set next to the tree bed, and fill the can with water. A layer of mulch also helps conserve moisture.
3. Keep the Tree Bed Clean
Removing trash and animal waste from the tree bed tells passersby that someone cares, which is likely to discourage them from littering themselves. It's true, picking up trash isn't as glamorous as picking flowers—but your tree will love you for it. Consider posting a small sign (tied—not nailed—to the tree) asking people to curb their dogs and not to litter.
4. Install a Tree Guard
You can hire a metalworker to install a guard around a tree bed or create your own. (The City no longer tickets people who install tree bed guards.) Guards help protect your tree from animals, foot traffic, and damage from cars and bicycles. Make sure the guard never touches the tree—monitor for this as the tree grows. Also make sure the guard allows water to flow into and out of the tree bed.
For more information on tree bed guards, check out our Tree Bed Guard tip sheet.
To Plant or Not to Plant
Tree beds offer great opportunities for city dwellers to exercise their green thumbs. Annuals, perennials, and bulbs can be beautiful additions to a tree bed as long as you remember that the tree's health comes first.
Flowers and plants bear witness to others that you are taking care of your street tree. Wilting flowers in the tree bed also provide a good reminder to water.
If you're not careful, though, planting in tree beds can do more harm than good! How? Overcultivating the soil damages tree roots, and raising the level of the soil in a tree bed to make room for flowers can actually kill a tree. It may take several years to show, but the damage to the tree is real. Moist soil or mulch mounded against the base of the tree can cause the bark to rot, provide an entry point for pests and diseases, or create a home for rodents to eat away at the tree base. Rotten or damaged bark at the base of the trunk can "girdle" a tree, strangling it to death. When a girdled tree dies, it can topple over from the base, often causing a lot of damage. Excess soil in a tree bed can also choke roots. Roots need oxygen, which they get from air trapped in soil. When too much soil is piled up, the air is squeezed out. Without oxygen, roots die, and without a strong, healthy root system, the tree will die.
Here's how you can plant in the tree bed without harming your street tree.
- Plant flowers or groundcovers with small root systems. That way you won't disturb the tree's roots to a great depth when you plant. Try small annuals like impatiens, or perennial groundcovers like bugleweed (Ajuga reptans) or periwinkle (Vinca minor)—avoid ivy. Small bulbs are good too: Try crocus, miniature daffodils, or glory-of-the-snow (Chionodoxa species). Stay clear of large shrubs and water-hungry plants. See the Tree Bed Plants tip sheet for more ideas.
- Don't raise the level of the soil by more than 1/2 inch. Instead, with a hand cultivator gently loosen the soil to a depth of 1 to 2 inches, removing soil if needed to accommodate your groundcover's root-balls.
For Newly Planted Trees
- If you see a newly planted street tree with burlap, tape, or wire wrapped around its trunk, remove it immediately. Left in place, the burlap can keep the trunk wet and cause rot, and tape or wire can girdle the tree.
- One year after a tree is planted, remove the guide wires and stakes attached to the tree at breast height so the tree can move freely (freedom of movement improves tree strength) and so the guide wires don't strangle the tree.
Take care of street trees—for a healthier city and a healthier you!