Inorganic mulch used (on left) for a fantastic effect – Tarry garden
Champion 2018 Spring Garden Competition

Thinking of sprucing up your piece of paradise in preparation for the 2019 Spring Garden Competition? Mulching might be the ‘icing’ on your garden ‘cake’ to make it look very spiffy for the judges come September. BUT choosing the ideal mulch is a very tricky decision. In this post I will outline the different types of mulch, the advantages of mulching, the disadvantages of mulching and my conclusion on what to choose.

There are three basic types of mulch:

  1. Inorganic mulch such as aggregate – gravel, decorative pebbles, crushed rock sand etc stuff that does not break down (as seen in image above).
  2. Organic mulch such as eucalyptus leaf litter, wood chips, pine bark chips, compost, lawn clippings, pea straw, stable straw, lucern hay, seaweed, manure, sugar cane mulch, paper etc – stuff that does break down.
  3. Living mulch this is any dense growing ground cover plants.

The advantages of mulching and the primary reasons to mulch:

  • Is to mimic growing conditions in a natural habitat;
  • Retain moisture by reducing evaporation – therefore more efficient use of water resources;
  • An effective and safe way to reduce weeds;
  • Using organic mulches will result in the soil benefiting from the addition of nutrients (ie nitrogen and other trace elements) as the mulch breaks down over time. This helps to create good soil structure, microbes and biological activity in the soil enhancing micro-organisms which will in turn, promote good plant health;
  • Protects the soil surface from compacting and erosion in heavy rain events (an important consideration on the Coffs Coast);
  • Using a living mulch (ground cover) will add diversity to the garden by adding additional texture, form and versatility.
  • By mulching, the garden looks pretty good too, it has to be said!

The disadvantages of mulching:

  • The soil needs to be wet/damp before the mulch is applied. Recently in Coffs there hasn’t been a lot of rain so it would be best if the ground was given a good soaking before mulching;
  • By putting too deep a layer of mulch where it becomes hydrophobic – that is the water doesn’t penetrate to the soil and the mulch repels water rather than letting it soak through;
  • The use of green material (lawn clippings) for mulching can be detrimental to soil health as it will break down the soil’s nitrogen supplies as it is used up in decomposition. By adding extra nitrogen (eg Blood and bone) to compensate for this before the application of the mulch is the way to go.
  • Sometimes the use of heavy layers of cardboard or paper may not be such a good idea as it may attract nematodes and be colonised by termites;
  • As organic material breaks down it coats the soil with a wax-like substance making the soils (and especially sandy soils) water repellent. Applications of soil wetting agents are very effective and well worth using to overcome this problem, if you have it;
  • One thing to bear in mind is NOT to use mushroom compost for acid loving plants eg azaleas, rhododendrons, hydrangeas, camellias, blueberries and some vegetables like sweet corn, cucumbers, beans, broccoli, zucchini and onions;
  • As organic mulch needs to be topped up every year or so it can be a bit expensive if you’ve a large area to cover;
  • Inorganic mulch can look a bit shabby over time as debris falls on top and this material can be difficult and time consuming to remove.
  • Living mulches require a lot of time to grow so patience is needed for this method.

Living mulch of Grevillea porinda Royal Mantle – Clague garden
winner Block over 4001 square metres 2018 

Mulching tips:

  • Prepare the area well by removing any grass, weeds and dead plants from the garden;
  • Plant new plants before applying the mulch layer;
  • Good mulching times are in mid spring or early summer (now is ideal);
  • If you are going to install a drip watering system, this should be done before the mulch is applied;
  • Do not pile mulch up against the stems and trunks of plants – this will encourage rot and perhaps the death of the plants;
  • If you are wanting to mulch Australian Native plants as a general rule these plants do not like nitrogen so an inorganic mulch might be best for this application. Rainforest plants are the exception of course, as they enjoy deep green organic material.
My conclusion?

Don’t really have one……… there are positive reasons for mulching including weed suppression, appearance, moisture retention and by the same token there are reasons for not mulching too – cost, work involved, imbalance of nutrients. So I guess it is really up to the individual and the garden itself.

There are many different mulches available from your local nursery or landscape supplier – Cypress chip/mulch, Hardwood chip/fines, Native Mulch, Pinebark (various sizes), Pine Sawdust, Red Diamond Chips, Tea Tree Mulch, Uni Mulch and lots and lots of Aggregate – river pebbles, gravels, volcanic rock etc.

My advice would be to have a good think about where you are going to mulch, what plants will be growing there, how much $ you’ve got to spend and what is practical for you to apply – not much point getting a tip truck full of heavy aggregate if you’ve a dodgy back.

If you are preparing your garden for the competition it would be best to get the mulching done now (if you haven’t already done it) rather than the days leading up to judging time. It settles well into your landscape and doesn’t have that ‘instant’ covering up look.


Happy mulching!