Approaches to creating great-looking decks
We wait years for trees and shrubs to mature, yet it’s often standard practice on construction sites to take out existing specimens, then spend thousands of dollars replacing them. While it may seem easier to wipe the landscape clean and start from scratch, existing plants can be more of an opportunity than a hindrance. Working an established tree into the design can turn an ordinary deck into a work of art. Sure, crews may need to tread a little more lightly and redirect their traffic patterns, but your client will have a better finished product and appreciate the landscaping dollars saved.
Protecting Plants During Construction
Broken branches and scarred bark are obvious forms of damage common to greenery on construction sites. But damage to plants below ground, though less immediately apparent, is also a concern. Soil compaction and damage to the roots by heavy equipment and intense foot traffic is the number one construction-related cause of tree and shrub failure. Soil compaction means less air and diminished permeability in the soil, which deprives roots of essential oxygen and water. It can take affected trees and shrubs years to decline, but they’ll eventually turn up dead as a doornail.
You can take simple steps to avoid inadvertently killing your customer’s prized azalea or dooming the tree you’re building a deck around. Before the project begins, use flagging tape to identify trees and shrubs in the work area that are keepers. Include plants anywhere your crew will be, not just where the project will be built. Don’t forget about parking and material-storage areas.
Next, establish a safety zone around each plant. It’s a good idea to put up temporary fencing (snow or silt fencing works fine) to prevent damage to trunks, stems, branches, and roots. One rule of thumb is to fence off at least a 1-foot radius for each inch of tree trunk diameter. Another good guideline is to place the barricade just outside the tree’s drip line (an imaginary vertical line that extends from the edge of the tree’s canopy to the ground). Because shrubs have less extensive root zones, a 3-foot radius around each plant should suffice.
To help minimize stress to plants during a long project, apply a 3-inch to 4-inch layer of wood chips in the safety zone and be sure plants get adequate water, especially during dry periods. This will help reduce compaction and retain soil moisture. There’s no need to use expensive mulch — you can often get wood chips for free from tree-trimming crews.
Also, don’t rinse out paint, stain, or other chemicals onto the ground; they can be lethal to plants. Likewise, warn your customer to choose a plant-friendly cleaner when it comes time to clean the deck. Many oxygen-bleach deck cleaners are reported to be safe to use around plants.
Designing Around a Tree
Great care must be taken when working trees into a deck’s design. Soil compaction should be kept to a minimum. If you’re raising the grade, a drywell must be built to keep the new soil away from the tree and ensure proper moisture and air exchange at the tree base.
Trees naturally flare at the bottom of the trunk. If the flare gets covered so that the tree resembles a telephone pole sticking out of the ground, the tree is headed for trouble.
For areas where the grade needs to be lowered, a retaining wall should be built around the tree (no closer than the drip line) to maintain the original soil level and leave the roots undisturbed.
If you face either of these situations, it may be a good idea to consult with an arborist certified by the International Society of Arboriculture.
When building a deck around a tree, don’t place the deck tight to the trunk. Give it plenty of growing room — leave 3 inches to 4 inches of clearance all the way around. If a tree is located in the center of the deck, consider circling it with a decorative bench. This will provide seating and prevent children, pets, and unsuspecting adults from having any mishaps at the gap. Alternatively, a guardrail or decorative containers could be installed.
To keep weeds from sprouting under a deck, lay in a thick layer of gravel to deprive weeds of light and keep seeds from reaching the soil. Organic mulch is not a good substitute for stone, as it retains moisture and will eventually compost. A few weeds may still poke through. I prefer to avoid chemicals when possible, so I’d suggest that your customers simply pull the weeds that make it through the gravel. They could also put down an annual dose of pre-emergent herbicide.
It’s almost inevitable that building a deck will cause some plant damage. Any dead, damaged, or diseased limbs or stems should be removed. Branches should be cut flush just at the branch collar (the swollen area where the branch connects to the trunk).
To prevent the weight of a large branch from creating a splintering break, use the three-cut method to prune. The first cut is made half-way through on the underside of the branch about 6 inches from the branch collar. The second cut is made clean through from the top, about 2 to 3 inches out from the first cut, removing the weighty branch. The third cut removes the remaining nub at the branch collar. Don’t treat pruning cuts with paint, tar, or any other products. It’s best to allow plants to heal naturally.
Consider removing any branches lower than 6 feet above the deck to prevent people from hitting their head. If you’re at all unsure about making a cut, call in a certified arborist.
It’s typical for deck construction to create some lawn damage. Worker traffic compacts the soil. Lumber piles kill grass. And trucks can make big ruts.
Ruts may need to be filled with topsoil. Areas with compacted soil or shade-killed grass need to be aerated and dethatched. You can rent machines that do this. After that, rake in a thin layer of compost, put seed down, and rake again, lightly, to make sure the seed is in contact with the soil and compost. Then, keep the area moist until the lawn is established. Putting down a thin layer of straw mulch, to keep the soil moist and protect seedlings from erosion and birds, is also not a bad idea.
Jennifer Benner is a horticulturist in Roxbury, Conn.