Climate Change, Lawn Thatch, and Ant Infestations
Garden Lawn under renovation by the GardenAdvice Team
Climate Change is Fueling Ant Problems in Lawns
As the climate warms, ant infestations in gardens and lawns are becoming more common. Warmer temperatures and milder winters create ideal conditions for ants to thrive and expand their colonies. In the UK, recent studies have noted a surge in ant populations partly due to rising temperatures – ants prefer warm environments and even benefit from extreme weather disturbances like storms or droughts, which can open up new habitat for them. This means that over the next few years, gardeners may face bigger ant problems as global warming continues. While ants are a natural part of the garden ecosystem and even help aerate soil, an overabundance can become a nuisance on lawns, especially when they form numerous soil mounds that disrupt the lawn’s appearance and usability.
Thatch Buildup Creates an Ideal Ant Habitat
Thatch is the layer of dead grass stems and organic debris that accumulates on the soil surface of a lawn. A thin thatch layer can benefit turf, but excessive thatch (more than ~1 inch) creates problems. One major issue is that thick thatch acts like a “thatched roof,” preventing water from penetrating into the soil. In older lawns that haven’t been maintained, this dead grass layer stays dry and warm – essentially a perfect, insulated shelter for ants to build their nests.
Ants typically establish colonies in lawns with a layer of thatch or dry dead grass, often compounded by a fungal condition called dry patch that makes the lawn surface hydrophobic (water-repellent). The dry, undisturbed environment under thatch is ideal for ant colonies, allowing them to expand without being flooded by rain or irrigation. Over time, these ant nests produce small heaps of fine soil on the lawn surface and can lead to uneven turf or patches of bare soil where grass struggles to grow. In summary, excessive thatch greatly increases the risk of ant infestation by providing ants with shelter and favorable nesting conditions.
The Role of Soil pH in Thatch Decomposition
Maintaining a healthy soil pH in your lawn is now more important than ever – not only for grass health, but also for controlling thatch and the pests that it harbors. Acidic soil (low pH) tends to inhibit the microorganisms (like certain bacteria and fungi) that decompose organic matter. When these thatch-decomposing microbes are less active, dead grass and leaf litter accumulate faster than they break down, causing a rapid buildup of thatch. This creates the dry layer that ants love.
For example, in one lawn analysis, an overly acidic lawn was found to have restricted grass growth, heavy thatch accumulation, and ensuing ant infestations – the thatch buildup essentially provided a dry roof for the ants. The good news is that correcting an improper pH can reactivate soil biology and reduce thatch. Microbial decay of thatch is most efficient when soil pH is in a neutral range (~6.5–7.0). Therefore, it’s advisable to test your lawn’s pH and, if needed, apply garden lime to raise the pH to an optimal range for turfgrass and soil organisms.
By keeping the soil pH balanced, you encourage earthworms and microbes to break down the dead grass layer more quickly. In turn, this deprives ants of their cozy habitat. In short, proper pH management helps your lawn naturally dispose of thatch and makes the environment less attractive to ants.
Treatments and Preventive Measures for Ant-Infested Lawns
Dethatching and Aeration:
Physically remove excess thatch by scarifying (raking) the lawn or using a vertical mower if the thatch layer is thick. Follow up with core aeration to alleviate soil compaction and improve airflow. Removing thatch takes away the ants’ shelter, and aeration helps water penetrate the soil. Regular annual scarification and aeration make the lawn less hospitable to ants and also promote healthier grass growth. Lawns that receive frequent mowing and maintenance tend to have fewer ant issues than neglected, thatchy lawns where ants feel “safe” to settle.
Adjust Soil pH and Fertility:
As mentioned, keep your soil pH in the optimal range. If your soil is acidic, applying lime will not only improve grass vigor but also accelerate thatch decomposition. A healthier, denser turf (supported by proper pH and fertilization) can outcompete moss and reduce bare spots, leaving less open ground for ants to colonize. Good lawn nutrition also helps grass recover from any disturbance caused by ant hills.
Proper Watering and Dry Patch Treatment:
Ants prefer dry, well-drained soil and typically avoid consistently damp areas. If your lawn has “dry patch” issues (areas where water refuses to soak in due to fungal waxy coatings in the soil), consider applying a wetting agent to rehydrate the soil. Regular watering of the lawn during dry periods can discourage ants – in fact, simply flooding active ant mounds with water can cause the colony to relocate, since ants do not like saturated soil. Just be careful to water in a way that the lawn grass can tolerate (e.g. avoid scalding hot water). Keeping the lawn adequately moist (but not waterlogged), especially in summer, can make your yard less attractive for ant nesting.
Biological Controls (Nematodes & Fungi):
For a natural, chemical-free treatment, you can introduce biological enemies of the ants into the lawn. One option is using a pathogenic nematode treatment specifically made for ant control. Products containing Steinernema feltiae (available as Nemasys No Ants in the UK) can be watered into the lawn where ants are active. These microscopic worm-like organisms enter ant tunnels and infect the ants, often causing the colony to die off or move away.
Nematodes are most effective when applied to moist soil in warm weather (typically late spring through summer) and may require repeated applications for full control. Another biological approach is the use of entomopathogenic fungi – certain naturally occurring fungi (such as Beauveria bassiana or Metarhizium anisopliae) are known to infect and kill ants and other insects. Research has shown that these fungi can cause high ant mortality in colonies, though results can vary. Some eco-friendly insect control products incorporate such fungi as the active ingredient.
When applied to the lawn, the fungal spores attach to the ants, germinate, and eventually kill the hosts, leading to a collapse of the infestation. Both nematodes and beneficial fungi are environmentally safe options that target ants without harsh chemicals; they essentially make the ants either die off or move on to new areas.
Targeted Ant Treatments:
In cases of persistent infestation, traditional ant control methods may be used carefully. For example, applying ant bait or powder directly into the nest can help eliminate the colony at its source. If you go this route, slice into the ant hill with a spade, then place the ant bait/powder deep into the nest tunnels (and cover it up) so that it reaches the queen and brood. This avoids spreading pesticide on the grass surface (which can harm your lawn).
Always follow product instructions and consider pet- and child-safety if using any insecticidal baits. As a gentler remedy, some gardeners have had success with household deterrents like diatomaceous earth, citrus oil, or soap solutions applied to ant areas, though these may only provide temporary relief. Boiling water is sometimes suggested but not recommended, as it will scald your grass along with the ants and leave brown patches.
Ongoing Lawn Maintenance:
Prevention is better than cure. Going forward, maintaining your lawn in a healthy condition will naturally reduce problems with ants. Regular mowing (so that the lawn is frequently disturbed), annual dethatching, and keeping the lawn well-fed and watered will all discourage large ant colonies from settling in.
Also, minimize bare spots and patch up any areas of thin turf by overseeding – thick grass coverage leaves less open soil for ants to excavate. If ant hills do appear, brush them out on a dry day before mowing so you don’t smear soil on your grass. Level any large mounds in the winter when ants are less active by removing the excess soil and re-turfing if needed. By combining these cultural practices with occasional biological treatments, you can keep ant infestations at bay even as the climate continues to warm.
