A tree pit guard is a low fence or border that is installed around the edge of a street tree pit. Installing wood, brick or iron tree pit guards around street trees is an effective way to protect them from the pedestrians, cars, dogs and pollution that threaten their health. A good tree pit guard should:

• Keep people from stepping on the soil around your tree. Repeated foot traffic compacts the soil and keeps air and water from getting to the tree's root system.
• Protect your tree trunk from damage caused by car doors, bike locks and other sidewalk traffic.
• Keep dogs from using your tree pits as a bathroom. Dog urine is acidic and can burn plants and tree roots. Dog feces are ugly and high in nitrogen. Both are harmful to trees.
• Prevent trash, chemicals, salt and other pollution from flowing into the tree pit.
  
  See examples of good tree pit guards.>>

Tree Pit Guard Regulations
In Washington, D.C., you do not need a permit to install a tree pit guard, but you must follow these guidelines:

• Your tree pit guard must never prevent car doors from opening. Tree pit guards that are shaped like planter boxes not only encourage people to pile mulch and soil into them, but they often prevent parallel-parked car doors from opening. It is illegal in D.C. to install tree pit guards that are more than 4 inches high on the curbside.
• Your tree pit guard must not restrict the growth of your tree. Make sure your pit guard will not girdle the tree trunk as it grows. Also take care to protect the tree roots when you install your tree pit guards. Don't forget, a tree can grow to be at least two feet in diameter!
• Your tree pit guard must never raise the level of soil around your tree. Filling up your tree pit guard with soil or mulch will suffocate your tree's roots and rot the bark on the tree's trunk. NEVER let soil or mulch touch the trunk above the level at which it was planted.
• Your tree pit guard must never become a trip hazard to pedestrians. Make sure your tree pit guard is large enough to be easily seen, and maintain it well so that loose bricks or timbers don't become a safety hazard.
  
  See examples of bad tree pit guards.>>

For a list of companies that can professionally install ironwork tree pit guards around your trees, click here.

How to Build a Timber Tree Pit Guard
Most treepits are 3 feet by 9 feet. Here are instructions on building a timber tree pit guard for your tree like the one in the photo above. Here's what you need:

• 5 4x4x8-foot pressure treated timbers (Adjust for extra large or extra small tree pits.)
• 10 galvanized 6-inch nails/spikes
• Electric drill with a drill bit just smaller than the width of your nails/spikes
• Circular Saw or Mitre/Chop Saw (Handsaw is OK too.)
• Extension cords or batteries
• Steel mallet or heavy-duty hammer
• Tape measure
  Pencil
• Safety goggles, dust mask and gloves

How to make it:

1. Measure the inside edge of the tree pit, length and width. The average D.C. tree pit is about 3 feet by 9 feet. Remember the adage: Measure twice, cut once.
2. Using 4x4x8 pressure treated lumber and the measurements of your tree pit, cut timbers as shown above. WARNING: Pressure treated wood is treated with chemicals to prevent rotting. Always wear gloves and a dust mask when handling or cutting pressure treated wood.
   
   The tree box is built like a log cabin, where the corner timbers overlap each other and create a solid joint. In order to allow this overlap, you will need to cut six timbers 3-1/2 inches shorter than the length or width you measured. (Believe it or not, a 4x4 timber is really 3-1/2 x 3-1/2 inches!). However, your seventh timber will be the full width of the tree pit, as shown above in grey
3. Once you have cut all the wood to size, you will need to bevel the upper curbside edges, so cars parked along the curb can open their doors without problem (See above). Using a miter box and handsaw or an electric miter saw, cut off the ends of the two upper widthwise timbers at a 45-degree angle.
4. Lay the wood in place around the inside of the tree pit to see how it fits together.
5. Using the electric drill, drill holes at each of the places indicated above. It helps if someone holds the wood steady while you drill through both upper and lower
   timbers at once.
6. Then use a steel mallet or heavy-duty hammer to hammer the spikes or nails into the holes.
7. Once you’ve finished making your tree box guard, be sure to complete your job by weeding your tree pit and applying 2 inches of fresh mulch. Just be careful to NEVER fill your new tree box guard with soil or mulch. Raising the level of the soil in the tree pit will strangle the trunk and smother the roots, keeping your tree from getting the air and water it needs to thrive.
8. Affix a dedication plaque to the front so everyone knows your tree is cared for and loved!