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Removing moss and hydrocotyle from lawns

I am having terrible trouble with my lawn this year. I have big patches of moss and hydrocotyle all over. I have spent many hours (and dollars) preparing, laying and caring for it and I am not doing anything different this year. Can you help me as I do not know what to do?


The first thing to understand is that moss grows in conditions that grasses do not enjoy. Because most grasses fail to thrive in winter, moss is able to establish and dominate a lawn in a short period of time. Moss can also tolerate long periods of drought in a dehydrated state — it rehydrates and grows again with rain in autumn.

The best thing to do is to remove it and improve conditions to prevent it from reappearing.

Increase the amount of sunlight — reduce shade, if possible, by pruning overhanging trees and shrubs.

Improve drainage. Unlike grass, moss does not require a good supply of oxygen in the soil to survive. Improve drainage by digging a drain back-filled with scoria, re-contouring the area with top soil to elevate it, or digging a sump and back-filling with scoria. Aerate the lawn to improve drainage using a garden fork.

Apply lime. Mosses enjoy acidic soil conditions. Lime will not kill moss, but will encourage better grass growth.

Remove thatch — a build-up of old grass, which forms a spongy layer that increases water retention and reduces grass vigour. Remove by raking.

Mow grasses in shady areas on a higher setting. This will increase the amount of leaf exposed to all available sunlight. Mowing too closely reduces grass vigour, and so eventually moss and weeds will take over.

Regularly feed lawns. Use a specially blended lawn fertiliser high in nitrogen such as Yates Gro Plus Lawn Food. This will encourage fast, lush growth. Apply in autumn and spring and water in after application.

Sow a type of lawn seed that grows happily in shady areas — fescue grasses are best.

Apply Sulphate of Iron. Iron compounds are effective moss killers and work quickly to stimulate grass growth. Sulphate of Iron comes in a handy 500 g pack. Mix it with water in a watering can, and apply. Over time, the moss will turn black and can be raked out of the lawn. Over sow with a suitable lawn seed. Some lawn fertilisers contain iron compounds to control moss such as Yates Moss Killer and Fertiliser.

There are many chemicals that control moss — Yates Surrender controls moss, algae, lichen and liverworts in lawns. Yates Moss Killer is also effective, giving long lasting control.

Chemical control will give only temporary results. Conditions need to be improved to encourage permanent good grass growth. To be effective, a combination of chemical control and cultural practices will be needed to achieve the desired effect of a green carpet.

Hydrocotyle can be controlled using Yates Hydrocotyle Killer or Woody Weedkiller. Spray on a fine, still day. Spray drift can cause damage to other desirable plants and some burning may occur on fine turf grasses. Avoid using clippings for compost or mulch for six months after treatment.

UnitecAdvice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH

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Last updated: June 27, 2005