To Use or Not to Use – Grass Clippings?

The clipping from your lawn can be a useful addition to the garden providing another source of nutrients as they decompose.   But…they may also be loaded with herbicides or fertilizers and thus become a bad addition to the garden.

If the lawn is watered often and fertilised frequently it will grow rapidly and need mowing often – usually every two weeks. This grass will contain lots of nutrients from the fertiliser and have thin cell walls due to its rapid growth. The combination of high nutrients plus thin cell walls makes it easy for Fungi and Bacteria to break it down rapidly, especially if the weather is warm as the naturally abundant Fungi and Bacteria will be very active.

As the Fungi and Bacteria need food to multiply they not only break down the grass clippings but they will draw in all available surrounding nutrients from the soil, especially the Nitrogen from ALL sources that would otherwise be available to the plants already growing in that garden.

This rapid take up of all nutrients means that the existing plants will be experiencing a temporary deficiency know as the Nitrogen Drawdown and so will not grow as well and may even exhibit some deficiencies; eg. The new leaves are pale, indicating a Nitrogen deficiency.

Some people say you should not put fresh grass clippings around a fruit tree as that will stop it flowering, and so fruiting.  This would be true only if you put a lot of fresh grass clippings from well fertilised grass that was watered often and was placed around the tree every time you mowed the lawn; ie. every two weeks.   The tree would experience Nitrogen Drawdown often with little chance to recover between fresh clippings being place around it again.

The Nitrogen Drawdown can be avoided by giving the tree a good complete balanced fertiliser application that is well watered into the soil so the roots can use the fertiliser before the grass clippings grab the nutrients first.  Placing a Compot near the tree and filling with organic waste will also boost the tree growth adding additional nutrients.

If a weed killer has been used on the grass within the past 5 to 7 days then the clippings will still contain active herbicide.  If those clippings are then spread onto the garden, any plant the grass clipping are placed near will be affected, either by killing them or retarding their growth, because the herbicide has not fully broken down by natural means. eg. sunlight, Bacteria, Fungi etc.


If you do not fertilise nor water often, and have not used an Herbicide recently, then yes it is useful to use the clippings as an Organic Matter supplement to add to your garden. Organic Matter is highly desirable as it holds moisture and nutrients giving the plants access to this water and nutrients while preventing the water and nutrients being washed down out of the plant root zone.

Fresh green vegetation should NOT be placed right next to the trunk of any plant including a fruit tree as the rapid decomposition will heat up and burn the bark often ring-barking the tree, thus killing it. Small quantities will not be harmful.

All the above is a simplified version of a very complex and interrelated reaction that is constantly happening within the soil all the time.   Any action that occurs will change the reaction and the results.   An action, such as disturbing the soil, can let in more water (from rain and/or irrigation), more oxygen and let more Carbon Dioxide out but also create a bare space that any weed seeds can drop into and establish themselves.

If you do use grass clippings (like Vicki) then covering the clippings each week with new clippings will usually smother any seeds attempting to grow from the last cover.   You will have to work out what works best for your individual circumstances, but hay, sugar cane mulch, straw or regular mulch are excellent alternatives for grass clippings.

Today’s Did You Know…?

When a person eats a root vegetable; eg. carrot; parsnip; they are actually eating the food stored by the plant that the plant needs to use for its next year’s growth, when it will flower, set seed and (I think) happily die.

A bi- annual plant (ie. one that grows in the first year and then sets seed the next year) may sometimes “bolt” so that it sets seed in the first year. This is because it has been grown out of its normal growing times so overlaps into a time zone when the days are getting shorter (or longer depending on the type of plant response to length of day- called Day Length). The plant is programmed in its DNA to respond to a combination of Day Length and Temperature so it then uses the stored food to flower, set seed & die.


The message from this is to read and obey the instructions from reference materials on when to plant seeds (or seedlings) in your climate area. A good indication is that your local nursery will have seedlings available at the correct planting time for your local area so make use of their local knowledge.