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Growing Grass Under Shade Trees

Uncle's Premium Shade Mix Grass Seed

Why grass will not grow under your shade tree.

Simply stated its "survival of the fittest." The trees out-compete turf grasses for all the resources necessary for life. Turf grasses grow best in full sunlight. Under trees, 95% of the sunlight is either reflected or used by the tree for photosynthesis. The quality of light reaching the ground under the tree is different than what is available in full sun. The grass plant reacts with a biological attempt to find more light.  Compared to grass plants grown in full sun, grass plants in the shade will be longer, thinner and less vigorous. These leaf changes will result in reduced tolerances to heat, cold, drought, wear, and disease.  Lack of vigor will affect turf density allowing weeds to move into the thin areas.

What would seem to be the most obvious resource in short supply would be light. While the area under the tree can be shady, it is rarely too shady, to grow turf. Little is required to germinate grass seed. The right amount of moisture, the right amount of heat and grass seed will germinate even with no light and no nutrient. Mother Nature designed her grass seeds to sprout in the deep shade of established grasses. Young grass plants can tolerate lower light conditions; however as grass plants mature more sunlight is required to maintain health and vigor. In full sun areas, grass blades reach to the sky to absorb the sunlight and thrive. In heavy shaded areas, the maturing grass plant is weakened by the lack of quality sunlight and suffers. Then, to complicate matters, an already weakened grass plant is forced to compete with an established shade tree for food and water.

How to keep the grass growing under your tree. 

  • Improving sunlight intensity and duration of quality light reaching the grass plant is important. The more time the grass plant has in full sunlight, the better it will perform. Pruning lower branches to raise the canopy will increase full sun exposure and allow more wind circulation helping to reduce humid conditions that can stimulate turf disease.
  • Shaded areas with restricted air movement may require treatment with Fungus Fighters to maintain a healthy turf. In addition, shade stressed grass plants are less tolerant of heavy wear, and traffic management may be needed.
  • Re-seed shady areas three times a year (spring, summer, and fall) rotating youthful, vigorous, low light tolerant grass plants into the maturing turf stand weakened by poor light conditions.
  • Use Uncle’s Premium Shade Mix. A blend of elite grass seed varieties with lower water and nutrient requirements showing improved shade tolerance and increased disease resistance.
  • Deep water shade areas!  We all know how difficult it is to keep the portion of the lawn in the sun moist where the only water consumer is the delicate root system of the turf. Imagine how much water it takes to sustain a full-grown tree having several acres of leaf surface from which water evaporates. In the spring, with frequent rains, the shade tree and grass are good neighbors, plenty for everyone. However, when spring rains stop and summer heat sets in, the trees get very unfriendly.  A large shade tree can use hundreds of gallons of water a day leaving a little moisture for the turf grass. Water heavy shaded grass areas heavily but infrequently in summer to reduce wet foliage. 

Compensate for unfair advantages. Make the soil under your shade trees less compact and increase its water holding capacity by core aerating and filling the aeration holes with PrimeraFC Field Conditioner.  PrimeraFC is a natural porous ceramic granule having incredible water holding capacity with the ability to relief compaction when tilled into the soil structure. Re-seeding can be done at this time using Uncle's Premium Shade Mix, at the heavy rate, covering seed with additional PrimeraFC.  Apply Loveland Golf Course Starter fertilizer to replace depleted nutrients and stimulate root growth. 

  • Uncle’s Tip: Fall overseeding for heavy shaded areas, under certain big trees, can be more successful when dormant seeded after the leaves have fallen in late fall or winter months. Weather permitting remove fallen leaves from the area to prepare the soil. 
  • Apply Uncle's Premium Shade Mix, at the heavy rate, covering seed using sphagnum peat or PrimeraFC.  
  • Apply Loveland Golf Course Starter fertilizer in April.
  • Avoid using pre-emergent herbicides over dormant seeded shady areas. Crabgrass loves the sun and heat, and you are not likely to have a huge problem with crabgrass in heavy shade.
  • Winter weather will not harm the dormant seed. Seed will germinate in the spring as soil temperatures warm. 

What about large tree roots?

Unchecked over the years, soil erosion, can expose shallow tree roots. Bare soil erodes quickly with no grass roots to hold soil in place. Top soil can be hauled in to cover  exposed roots, but too much soil can be damaging for the tree. Gasses must pass from the air to the roots and from the roots back to the air. Too much, soil pack can create real problems for the tree so, be careful! Some surface roots can also be removed. Large surface roots are more for anchorage and with expert help, you may be able to remove a few. Always contact an arborist for advice on removing tree roots.  

If all else fails, start a shade garden. Hosta, astilbe, hydrangea love the shade.

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