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Brains Trust

MULCH

When is the best time to mulch my garden?

Soil never wants to be bare, so whether you use your plants as a living mulch or cover the soil around your plants, always ensuring you don’t have exposed or bare soil reduces degradation. There are times though when a thick layer of mulch is not a great idea, like in winter with its heavy rainfall periods because young plants can rot if mulch is too thick and soggy around their bases. Mulch will hold moisture in the soil, so summer is a great time to ensure plants are mulched well. Just make sure your soil is well watered before spreading mulch and water again once it’s spread. Ensure mulch isn’t hard up against plants where they emerge from the soil, to reduce the risk of rotting and allow airflow.

What is a living mulch?

A living mulch is annual plants that can fill the gaps between your plants to cover any bare soil, but can also give the added benefit encouraging predator and pollinator insects. This is a great practice as it keeps the soil covered, retains moisture and feeds soil life. Some great living mulches are buckwheat – a nitrogen-fixing plant that is also popular with bees and nectar-feeding beneficial insects – alyssum is a wonderful ground cover that supresses weeds and is a favourite for beneficial insects like lacewings and hoverflies; and calendula, a great companion plant for carrots, peas, asparagus and tomatoes, but also an edible flower. The best thing about all of these living-mulch plants is that they self-seed readily, so you will only have to plant them once.

Is a green-manure crop the same thing as living mulch?

A green-manure crop is similar, but is grown with the intent to terminate it before it flowers and sets seed. A green-manure crop is turned back into the soil or ‘chopped and dropped’ to cover the soil and left to break down on top of the bed. Green-manure crops are a great way to add nitrogen and feed your soil. As well as adding nitrogen, they feed worms, open up compacted soils and are a great soil fumigant.

You can purchase a green-manure mix, but you can also make your own by keeping out-of-date seed, beans and legumes from your pantry – and even chook grain works well. Just remember to chop it down before it flowers and goes to seed.

What is the difference between organic and inorganic mulch?

Organic mulch is something that has lived before such as wood chips, hay, straw and plants, while inorganic mulches can be pebbles, rocks or even weed matting. Inorganic mulches will not break down so are good for areas that have permanence, while organic mulches will slowly break down and will add back to the soil, so better suited to vegetable and ornamental gardens.

I’ve heard arborist’s pine mulch will inhibit plant growth? Is this true?

As a general rule, no. Whether it’s arborist’s mulch or pine bark, pine mulch is slightly acidic, so it can lower your soil’s pH and make it a little more acidic. But overall, the benefit of mulching will outweigh any disadvantages and, in some cases, acid-loving crops such as berries will appreciate it.

Some people worry about pine mulch stripping nitrogen from the soil over time due to the tannins being released as it ages. However, my experience has shown that any organic mulch is beneficial and using a handful of blood and bone or aged chook manure will add back any nitrogen you may lose from adding pine mulch.

Our own observations of how our plants are looking is the greatest indicator. The same rules apply for sawdust, but always make sure it’s not from treated wood which contains copper chrome arsenate (CCA) which could leach into your soil.

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