Landscaper Pro Advice:  Dealing with Shade

Shaded turf areas can be a big problem.  Most turf managers will need to manage and improve these at some stage.  Lawns are often close to houses, garages and sheds, or surrounded by trees and shrubs, and this will affect the health, vigour and the density of the sward.  It can be difficult to make the turf look good and present problems with moss, weeds and turf stress.    Unfortunately, in many instances it is impossible to remove the structures responsible for the shade and the grass plants must continue to grow in reduced light.  But you will be pleased to learn that there are strategies that turf managers can utilise to maximise grass health and presentation.

How does shade affect grass growth?

Most cool season Northern European grass species need 4-5 hours of direct/filtered sunlight each day and will be affected by the intensity, quality and duration of sunlight they receive.  Shaded conditions reduce the light reaching the plant and so the level of photosynthesis that can be achieved by the turf and therefore lowering carbohydrate production.  Carbohydrates are essential to plant growth as they provide building blocks for structural components such as cellulose (important for building cell walls) and they deliver energy for plant growth.

Where carbohydrate production is reduced as a consequence of shade, growth is weakened.  Grass plants have fewer tillers, less rhizomes and reduced rooting and will often display symptoms of elongated growth, a finer leaf texture and softer growth that is less tolerant of wear.  The result is a less attractive sward, lacking vigour and with a heightened susceptibility to drought, cold, heat and disease infections.

Structures and/or vegetation that cast shade often also serve to reduce air movement resulting in a rise in relative humidity and an increase in soil and leaf wetness following rainfall or irrigation as well as extended dew retention.  As a consequence, shaded turf is also more vulnerable to moss and algae invasion as well as disease infections.

Top tips for dealing with shade

In the first instance always ensure that shade is minimised as far as possible:

• Always think carefully about the growth habit and canopy size of trees and shrubs before introducing them into a garden or around a grass area. This is particularly important in small spaces.  Some species have small leaves which allow sunlight to filter through (e.g. many species of birch) whereas others have very dense, thick canopies which will prevent any light penetrating to the underlying grass (e.g. oak and beech).  Evergreen conifers are even worse as they cast shade all year round and not just through the growing season like deciduous species.

• Shallow rooted trees should be avoided at all costs, as they will compete heavily for water and nutrients potentially weakening growth and making the shaded environment even more difficult for the grass plants to cope with. Species such as willow and poplar can be particularly problematic, especially where subsurface drainage is installed as they will block pipes in search of water.

• Remove physical structures or large vegetation from the eastern and southern horizons as these will primarily be responsible for casting shade. If removal is not an option, selective pruning can make a significant difference, especially if the canopy can be lifted and thinned to increase light penetration and air movement.  Professional advice on the correct strategy for pruning and removal can be sought from a tree surgeon.

• Portable objects such as play equipment should be moved on a regular basis to spread wear and also to prevent the turf becoming too stressed as a consequence of shade.

Where shade cannot be avoided, the following strategies will help the grass plants to cope with the less than favourable growing environment and maintain levels of sward health and presentation:

• Always remove debris dropped by trees and other vegetation as soon as possible as this will smother the underlying grass as well as adding to the organic debris formation at the base of the sward.

• Always increase the height of cut of turf growing in the shade and mow less frequently. This increases the leaf surface available to capture sunlight and will allow the plants to increase root depth to access vital water and nutrients.  The extent to which cutting height should be raised will depend on the sward species composition and the time of year but allowing 10-25 mm of additional growth should be adequate.

• Fertiliser applications should be applied with care to avoid the creation of soft growth vulnerable to wear and disease infections. Aim to apply a reduced rate of a controlled release fertiliser product in spring, approximately 4-weeks prior to trees coming into leaf.  If required, a second application can be made in autumn, just prior to leaf fall, when a high potassium product should be used with the aim of hardening off the turf (see Landscaper Pro: Stress Control and Landscaper Pro: Pre Winter).

• Apply water only when required to keep the surface as dry as possible. Where required, especially where surrounding trees are competing for water, apply infrequently but deeply.

• Always aim to remove morning dews using a soft brush or switch to help the turf dry out and reduce its vulnerability to disease infections.

• Check soil pH. Debris dropped by trees and other vegetation, especially pine needles can lead to a reduction in soil pH.  If the soil pH is below the recommended level (5.0) grass growth will be even weaker and conditions will tend to favour the development of moss and algae.

• Renovate using shade tolerant grass species and/or cultivars (see Landscaper Pro: Sun & Shade). Creeping red fescue (Festuca rubra) and Chewings fescue (Festuca rubra commutata) tend to perform well in shade whereas many ryegrasses struggle.

• Control moss to minimise competition with the grass plants for light, water and nutrients.

Shade is a common problem for turf areas, affecting aesthetics and turf health.   Whilst every step should be taken where possible to increase the sunlight reaching the turf, some action can be taken to improve turf quality and reduce the effect shade has on the grass plant.