To Use or Not to Use – Grass Clippings ?

Lawn Clippings
Lawn Clippings

To Use or Not to Use – Grass Clippings? That is the big question for many gardeners. Personally I find them a useful addition to the garden providing another source of nutrients as they decompose, a cheap and free garden cover and they turn into beautiful soil right where you put them on your garden bed without the usual turning required if you put them into a bay compost system or other above ground composting system.  

But…and there is a But….They may also be loaded with herbicides or fertilizers if you have sprayed your lawn to remove weeds or fertiliser to improve your grass growth, if your thing is to have a beautiful lawn. Thus they can become a bad addition to the garden.

Nitrogen Drawdown

Fertilising the Lawn
Fertilising the Lawn

Nitrogen Drawdown occurs when Fungi and Bacteria rapidly multiply from the presence of easily accessible Nitrogen in the soil forcing them to draw in all other available nutrients from the surrounding soil especially the Nitrogen from ALL sources that would otherwise be available to the plants already growing in that garden.

This occurs when 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 produce grass with 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.

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 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.

How to avoid Nitrogen Drawdown

Nitrogen Deficiency
Nitrogen Deficiency

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.

Nitrogen Cycle

Nitrogen Cycle representation

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 me) 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. However from several customers (and myself), sugar cane mulch appears to attract rats. This may not happen in all gardens but it is something you need to be aware of in case you already have a rat problem in your garden.

Today’s Did You Know…?

Multicoloured Root Vegetables
Root Vegetables

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.


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