A yard with low spots or heavy clay soil can quickly become a saturated environment, creating a challenging situation for landscape design and tree health. Most trees are not adapted to have their roots consistently submerged in water, which leads to root suffocation and eventual death. When soil air pockets fill completely with water, roots cannot perform the respiration necessary for survival. It is necessary to select species specifically evolved for these conditions. Fortunately, many native species thrive in poorly draining areas, offering an opportunity to create a robust and beautiful landscape. This guide provides recommendations for trees that tolerate or prefer wet soil, along with specialized installation techniques.
Understanding Saturated Soil
From a tree’s perspective, “wet soil” is defined by a lack of oxygen in the root zone, a condition known as anaerobic soil. Healthy soil is composed of roughly half solid matter and half pore space, ideally split between water and air. When soil becomes saturated, water fills all the pore space, pushing out the oxygen that tree roots require for metabolic functions and nutrient uptake. This oxygen deprivation leads to root stress and can cause root rot from pathogens like Phytophthora.
Prolonged saturation prevents the development of fine feeder roots necessary for absorbing water and nutrients, effectively starving the tree. To determine the drainage rate of your soil, perform a simple percolation test. Dig a hole about 12 inches deep and wide, fill it with water, and allow it to drain completely overnight to saturate the soil. Refill the hole the next day and measure how many inches of water drain per hour. If the water level drops less than one inch per hour, the soil is poorly drained and challenging for most non-wetland trees.
Recommended Deciduous Trees for Wet Areas
Deciduous trees native to floodplains and swamps have evolved adaptations to endure extended periods of soil saturation. The River Birch (Betula nigra) is one species, valued for its striking salmon-pink to reddish-brown exfoliating bark that provides winter interest. This fast-growing tree typically reaches 40 to 70 feet tall and 40 to 60 feet wide. It tolerates both heavy clay and standing water, though it prefers slightly acidic soil to prevent leaf yellowing.
Another excellent choice is the Swamp White Oak (Quercus bicolor), a large, stately tree growing 50 to 75 feet tall with an equal spread. This oak is highly adapted to wet, acidic soils and tolerates seasonal flooding and soil compaction. Its leaves are dark green on top and silvery-white underneath, creating a distinctive two-toned effect that shimmers before turning golden-yellow in the fall.
The Bald Cypress (Taxodium distichum) is a majestic, long-lived conifer that is deciduous, shedding its soft, feathery needles each autumn after they turn russet-red. This species is known for its tolerance of standing water and can grow 60 to 80 feet tall. It develops a stately pyramidal form when young and a broad, flat top as it ages. In wet conditions, it may develop characteristic root structures called “cypress knees,” which protrude above the soil or water line.
The Red Maple (Acer rubrum) is one of the most widely planted shade trees due to its tolerance for diverse conditions, including wet soil, earning it the nickname “swamp maple.” Growing 40 to 60 feet tall with a rounded canopy, this tree is known for its brilliant fall display, ranging from yellow to scarlet. Its ability to grow shallow, extensive lateral roots allows it to thrive in poorly aerated sites, though it performs best in acidic soil.
Recommended Evergreen and Smaller Trees for Poor Drainage
Finding evergreen trees that thrive in saturated soil can be difficult, as most conifers prefer well-drained sites. The Bald Cypress is an exception, offering a coniferous appearance for most of the year. Other evergreen options are generally smaller trees or large shrubs that can be trained. Arborvitae (Thuja) species generally prefer moist, well-drained soil and may suffer from root rot in standing water. However, some varieties of Eastern Arborvitae (Thuja occidentalis) show moderate tolerance to heavier soils.
For smaller, ornamental options that handle wet ground, several native dogwood shrubs are excellent choices and can be pruned into small, multi-stemmed trees. The Red Osier Dogwood (Cornus sericea) thrives in consistently wet to boggy soil, making it perfect for rain gardens and low-lying areas. While usually a large shrub, it features bright red stems in winter and reaches a mature height of six to nine feet.
The Tatarian Dogwood (Cornus alba) is similarly adaptable to wet soils and offers vibrant red stems, sometimes growing up to ten feet tall. Its colorful winter bark makes it a functional choice for smaller yards or near water features. These smaller, wet-tolerant dogwoods provide year-round color without the risk of failure associated with planting sensitive species in poor drainage.
Specialized Planting Techniques
When installing a tree in an area with poor drainage, the standard planting method must be modified to prevent root suffocation. The primary technique is “mounding,” or planting the tree high. This involves setting the top of the root flare three to six inches above the surrounding grade. This elevation ensures the root crown remains above the saturated zone, allowing for better oxygen exchange.
The planting hole should be two to three times the width of the root ball but no deeper than its height. This wide, shallow excavation encourages the tree’s roots to spread laterally into the native soil rather than diving deep into the poorly draining subsoil. Use only the native soil as backfill and avoid adding amendments like compost or peat moss into the planting hole.
Amending the soil in the hole creates a pocket of porous material surrounded by dense clay, resulting in the “bathtub effect.” Water drains easily into the improved soil but then hits the clay walls and accumulates, keeping the root ball constantly soaked. Instead, soil improvement should be done after planting by spreading a thin layer of compost and mulch over a wide area around the tree, which gradually improves the native soil from the top down.