By Michael Sutton – AusGAP Your Turfgrass Purity Assurance

Achieving a healthy turf surface is directly reliant on soil composition and optimum water levels. The connection that occurs between water, soil and plant is imperative in the establishment of new turf and in the continued success of an established surface. Water, soil and turf must be united and work together to ensure healthy growth in any situation.

Simply put, water and soil are the main natural resources that act as factors of life in a turf environment. Turf needs soil as a growing medium and nutrient contributor, along with waters metabolic process to replace water loss via transpiration and as a diluent and carrier of nutrients needed by the plant.

When one of these components are out of balance, the performance or growth of turf can be compromised. An important aspect to examine in troubled areas of turf is the movement of water through the surface into its root zone. Correct volumes and occurrences of this process are crucial in supporting the turf profiles transpiration cycle. Accessibility of moisture within a turf root zone and the level of moisture in the soil are important factors that can influence turf performance and appearance.

It is important to maintain the association between water, soil and turf to enable the best growth and production. Knowing a soil type and how much water it requires, how it supports turf growth and how it aids in creating a superior turf are important in maintaining this association between water, soil and turf.  

More often than not, people will evaluate turf watering requirements by the colour of the grass, this method however, does not work sufficiently. Turf that is watered correctly does not always have less colour than an overwatered turf. When turf is underwatered, it can create detrimental long-term effects to the plant as well as influencing the colour.

Once you have determined the soil type, an approximate range of the soils water holding capacity is necessary. Key factors in watering frequencies and amounts are:

Soil Types

The type of soil that the turf is grown in is an essential aspect and should be examined and determined before watering established turf or the laying of a new turf area.

The first thing required is to determine the soil type. This will assist in a number of things, but most particularly the amount of water the turf will need. The main five (5) soil types are:

  1. Clay
  2. Clay Loam
  3. Loam
  4. Sandy Loam
  5. Sand

The easiest way to test what type of soil you have is by placing a small amount of site soil in the palm of your hand and then adding enough water to make it into a pliable ball. The following outcomes will determine the soil type:

  1. If the soil won’t form a ball, doesn’t stain your hands and has a gritty feeling, it is SAND.
  2. If the soil forms into a ball that can be rolled into a cylinder that breaks when gently bent and has a gritty feeling, it is SANDY LOAM.
  3. If the soil forms into a ball that can roll into a cylinder that doesn’t break when gently bent and doesn’t feel gritty, silky or sticky, it is LOAM.
  4. If the soil is like LOAM, feels sticky and can made to have a smooth outer layer, it is CLAY LOAM.
  5. If the soil features are sticky, with a very smooth outer later, sticking together stronger than anything else, it is CLAY.

Once you have determined the soil type, you will be provided with an approximate range of the water holding capacity.

Soil water holding capacity

The total water holding capacity will differ for each of the soil types, as well as the plants available water content (Table 1).

Evidently, soil texture influences water holding capacity, with Table 1 below revealing that loam soils have the most plant available water. Sands have the smallest moisture retention, with clays having the highest. It is important to note that a portion of moisture in all soil types is held too tightly to be available for plants to uptake.

Table 1: Suggested Total, plant available and unavailable water holding capacity of different soil texture types.

Important notes about water holding capacity:

  • Organic matter can improve water holding capacities of sands. Often very high sand content soils or root zone mixes can be assisted from the addition of a well-decomposed organic amendment. Too much organic matter, however, may be unfavourable and reduce soil aeration creating unnecessary moisture held within organic matter, which can create a waterlogged soil.
  • Another factor that can increase soil-water content is the control of the water table within 600mm to 1.2m of the soil surface. Water will rise above the free water table by capillary (adhesion and cohesion forces) action, this zone is called the capillary fringe. Fine-textured and organic soils have the greatest capillary rise, and this can be used to sub irrigate turf in some situations.

Soil Infiltration

Soil infiltration is the movement of water into the soil surface. Consequently, soil surface conditions are of prime importance. Other elements that effect infiltration are soil texture, structure, slope, and current soil- water content.

  • Sandy soils may have infiltration rates in excess of 25mm per hour, while clay soils are often less than 2.5mm per hour (Table 2 below).
  • A well-structured soil will provide large macropores (> 0.10 mm diameter pores, also called non-capillary pores or aeration pores) for infiltration, compared to a tight clay or compacted soil with few macropores.
  • Organic matter often aids infiltration by providing a better-structured soil.
  • Cracks that develop upon drying can markedly increase initial infiltration rates after irrigation. These are especially beneficial on heavy clay soils.
  • A sloped surface will exhibit a much lower infiltration rate which can complicate watering, particularly on rolling terrain.
  • Thatch can reduce infiltration if it becomes hydrophobic (water-repelling) in nature. Observations made in hydrophobic sands that have very low infiltration rates, are usually caused by organic coatings on the sand particles that repel water.
  • When water is applied to a dry (or partially dry) soil, the initial infiltration rate is high and then gradually decreases as water content increases.

Table 2: Representative infiltration rates for different soil textures. Surface conditions can cause these values to vary.

Techniques to improve infiltration rates depends on the particular factor that limits the soils infiltration rates:

  • On soils with poor infiltration rates, a good aeration/cultivation program can be very beneficial.
  • Allowing the soil surface to dry between irrigations can increase the initial infiltration rates by causing soil cracking.
  • On heavy clay soils, irrigation programs to apply a long run of water initially, followed by shorter runs with time in between for infiltration to occur. This is called pulse irrigation and would be in contrast to irrigating at very low rates (to match saturated infiltration rates) over long periods, or at higher rates that can cause runoff.
  • Application of organic matter to the soil surface of badly structured soils can improve infiltration. The easiest way to add organic matter is by growing a healthy plant and returning clippings. Well decomposed organic materials applied as topdressing may be useful. However, these should be applied in conjunction with a good core aeration program to prevent surface layering.
  • Breaking up any surface layer, whether from compaction, or a distinct textural change, will improve infiltration. For example, profiles containing a silt-loam soil laid over a sandy root zone mix will result in slow moisture penetration as the silt loam establishes the infiltration rate.
  • If a hydrophobic sand is the cause of poor infiltration, wetting agents may be beneficial to rewet the surface and aid in water absorption.

Readily Available Water (RAW)

Soil readily available water (RAW) is the water that a plant can easily extract from the soil (see Figure 1.).

RAW is the soil moisture held between field capacity and a nominated refill point for unrestricted growth. In this range of soil moisture, turf is neither saturated or at wilting point (heat stressed).

Turf roots will continue to take water from the soil after the refill point is reached. However, this water is not as readily available to plants and the crop finds it difficult to extract. If the soil dries to the permanent wilting point, the plant can no longer remove any water from it (some water may still be present but is completely unavailable).

The drier the soil, as shown by wilting point, the more water needs to be added to bring the soil back to field capacity.

Turf Soil Profile

The depth and quality of soil beneath turf dramatically effects the water retention properties and its capability to endure dry periods. It recommended for consistent turf appearance and durability that a minimum depth of 100mm of quality soil within the profile of most turf varieties consisting of:

  • Quality loam with sand, silt and clay components; and
  • Organic matter/humus.

When laying new turf, a quality underlay with a minimum depth of 100mm to suit your soil type is recommended. Additionally, organic matter or wetting agents can be applied to turf after laying and during profile renovations, to aid in improving soil retention properties.

It is recommended to ask a turf professional for further information on turf profile improvements, underlay and requirements, etc., prior to install or at time of turf purchase.

Seasonal Changes and Climate

With regular watering and basic care, you can create immaculate turf areas no matter the season. As stated previously, one of the first things you have to determine is how much water your soil can absorb before run-off occurs. This can be accomplished, by timing the interval between watering commencement to the point where no more water can be absorbed (i.e., run-off).

It’s important to note the two different groups of turf varieties, warm season and cool season turf varieties. Warm season turf varieties struggle in temperatures below 3° C (couch, kikuyu, buffalo, etc.), preferring warmer temperatures, where cool season turf varieties can tolerate temperatures below 0°C (rye, fescues, bent grass, etc.) but in contrast struggle during warmer conditions.

To help with this, below is a basic seasonal guide to watering turf for the most common of the types in Australia, warm season turf varieties.

Summer Watering

Watering your turf during the summer months of December, January and February could pose some challenges if you do not have an automated irrigation system. The Australian sun can leave soil profiles bone dry, leading to dried out or even grass death, due to water restrictions and drought events.

Most common turf types in Australia during this season can endure prolonged periods of time without water. They tend to lose colour and become brown and dry, but can redeem their appearance after irrigation, watering or rainfall reoccurs. This is because unirrigated turf surfaces in summer will enter a period of dormancy, where they shut down tissue growth to preserve moisture loss.

Once established, turfgrasses with some level of drought tolerance will not die when the turf plant reaches its permanent wilting point. When the period of drought ends, when it either rains or you recommence irrigation or watering of the area, the turf will be able to regenerate. However, keep in mind the ability to self-repair and recover from extended periods of little or no irrigation is only possible once a turf is fully established.

It’s important to not let newly laid turf go without irrigation while still establishing, especially during the warmer summer months. With limited root systems and drier soil, the grass may not survive extended periods of drought and can wither and die. In this instance, new turf will need frequent watering until it is fully established.

How often should I water turf in summer?

Turfs growth rate is directly related to how much water and fertiliser is used, and ultimately how much wear and tear it endures. If turf is continuously bearing foot traffic and activity – it will need larger water inputs than an area that has little or no foot traffic. The amount of direct sun or shade turf receives will also need to be considered, as turf in full sun environments will dry out quicker than areas protected by some shade, usually cast from a home, established tree/s, or a fence.

Established turf water requirements can often be met through natural rainfall or existing soil moisture storage, so minimal watering may be required. Australian turf varieties can be extremely resilient, adapting to our harsh climates.

During the warmer months developing a tradition of weekly watering, or sometimes twice weekly during peak summer periods (usually long hot February days), the turf will learn to survive with less applied water. Instead of watering every day for 10 minutes, it is much more effective to water turf once or twice a week for 30 – 60 minutes at a time, depending on method of irrigation.

Autumn Watering

During the Autumn months of March, April and May, turf may need lighter and less frequent watering. As the temperature begins to drop, now is the time to focus on reviving and repairing turf areas. Summer may have left your lawn lacking in density and colour, so now is a good time to repair those brown patches or even lay down new instant turf.

Warm season turf varieties slow considerably in growth during cold temperatures, so the more sunlight you can expose it to the better.

How often should I water turf in autumn?

Autumn is best to water turf in the mornings, as evening watering can encourage fungus growth due to the lower temperatures. Watering turf which has had an early morning frost settle on it can also help to reduce the effects of frost burn, which in some regions can severely discolour and dry out the leaf blade.

A good way to check soil moisture is to push a screwdriver into the soil, and if it doesn’t go effortlessly past 100mm, watering needs to be increased. Up to 40mm per watering application at one time is recommended.

Winter Watering

During the winter months of June, July and August, there are fewer daylight hours and an increase in shade and moisture. Warm season turf varieties will become dormant meaning that watering established turf in winter may not be necessary. The amount of winter rainfall in most Australian states will be adequate to sustain the growth of your turf during this time.

How often should I water turf in winter?

You may need to water your turf once a month, particularly if it has been a dry winter. If you do choose to water during this time its recommended that less, approximately once a month or longer, up to 40 minutes in duration is the best practice. Avoid over-watering as this could lead to waterlogging, fungal diseases and other environmental issues.

Spring Watering

The spring months of September, October and November bring extended daylight hours and wetter temperatures. It is the perfect time to conduct turf renovation maintenance to help encourage growth and vibrancy. In spring, turf areas may still have a lot of water retention from winter, so it’s best to water as needed.

How often should I water turf in spring?

In Spring the application of minimal watering over and above any naturally occurring spring rainfall should be limited. A deep soaking once a week is usually sufficient if no rainfall, depending on your location and climate. To check if your turf needs watering, push your finger into the soil profile, if the soil is damp, no water needs to be applied.

Avoid over-watering as this could lead to waterlogging, fungal diseases and other environmental issues. Up to 40mm per watering application is recommended.

Watering Efficiency

It’s essential that turf is given the water it needs to grow, but in an environmentally responsible way. Drought conditions and the continuing uncertainty of water restrictions around Australia, has led to an increased importance for watering efficiently. The use of water tanks, grey and bore water reserves to irrigate turf, are ways of decreasing the demands on local water supplies.

Efficiently watering turf comes down to four (4) key factors:

  1. Understanding your watering procedure output.
  2. Watering at the right time of day to limit evaporation.
  3. Avoid unnecessary runoff.
  4. Use of the correct method or equipment.

Understanding your watering procedure output

Before turf is watered efficiently, knowing that the existing watering procedure output is adequate can be established as follows: 

Step 1 – Check the water distribution for uniformity. You will need 4 containers; like catch cans, milk cartons or soup cans that are all the same size.

  • Place the 4 containers in a grid pattern on the turf area you are checking.
  • Apply water or run irrigation sprinklers for at least 10 minutes. If you have several irrigation stations that cover the area, run each station for the same amount of time.
  • Check each container to see if the amount is the same.  If you are not using the same size container or used a tin can and cannot see through to check the water level. You can pour the water into a measuring jug/cup, noting the volume each container contained.

In the case that there is uneven coverage, dry spots in the turf area can appear. Adjust turf watering technique and/or sprinklers until it covers the area evenly. 

Step 2 – Determine the amount of water to apply.

  • Empty the water from the 4 containers and measure 13mm up from the bottom of the container.
  • Place the 4 containers in a grid pattern on the turf area.
  • Apply water or run irrigation sprinklers on and start a stopwatch.
  • When your containers are filled to the mark, stop the stopwatch and turn the sprinklers off.

Now you know how long it takes to water turf areas. If it is recommended to water 25mm each week, then you would water three times a week for the amount of time it took to reach the 25mm mark on your containers.

Watering at the right time of day to limit evaporation

Watering time will have a significant effect on how efficient the technique or type is. Certain times can contribute to water loss and waste. For example, watering in the heat of the day when the sun is hottest or on a windy day, will result in more water lost to evaporation and there may be no need to water after rain event.

The ideal time of day to water is in the early morning, this will allow time for the water to absorb and provide moisture to the grass for the heat of the day. Keep in mind that it isn’t recommended to water in the late afternoon or evening, as the water may sit on the lawn overnight, creating an opportunity for fungi and other turf diseases to develop.

Avoid unnecessary runoff

Runoff is the result of applying water too quickly and can be dependent on the soil type. It may be a result of the soil profile not being able to absorb the amount being applied where it pools and runs off. At that point, stop watering and allow the water to soak in. Once the water has soaked in, resume watering to give the soil profile the necessary water requirement.

Soils with high clay content, as well as compacted soils tend to have an inability to absorb water quickly. With these soil profiles, you will almost certainly need to break up your weekly watering to ensure the soil absorbs the water. In these soil types aeration will aid water absorption, as this loosens the soil and gives water easier access to the turf root zone.

Runoff can also cause pollution issues when it drains into local waterways, as it can carry fertiliser, animal waste, and other nutrient-rich pollutants.

Use of the correct method or equipment

The method or equipment used has a definite effect on the efficiency of water applied to turf. For example, swinging sprinklers are the least efficient as water shoots up into the air and not directly towards the ground. The use of sprinklers that direct water spray with large droplets directly to the ground are more efficient.

Well maintained in ground irrigation systems are the most effect way to ensure that your turf is receiving the required amount of water it needs.