On mulch!

May. 28th, 2011 01:17 pm
moonvoice: (totem - wombat)
[personal profile] moonvoice posting in [community profile] oz_native_gardening
Mmm, delightful mulch! Australian natives do remarkably well when mulched with an appropriate mulch. For a relatively inexpensive outlay, mulch has long-term rewards and benefits for the plants, as long as you do your research and know what to look for.

Here's why mulch is awesome:

1. It slows evaporation, thus retaining precious water, especially in arid environments.

2. It keeps the roots cool, which prevents heat stress. Many Australian natives have grown used to a bed of leaf litter on their roots thanks to undergrowth and the heavy shedding habits of many eucalyptus and shrubs; mulch mimics this and keeps roots happy.

3. It either stops the establishment of weeds (or drastically slows it down). And prevents the growing of invasive grasses.

4. A good mulch breaks down over time, adding humus to the soil. This improves soil structure.

5. Reduces run-off and erosion during heavy rain. That speaks for itself really.

6. It makes a garden pretty. What's the point in having a garden if you can't enjoy it's beauty? Mulch, which comes in many colours, often dark and very flattering to the greens found in Australian native plants, is a unifying product that makes plants and soils healthier, while creating a greater sense of wholeness in the overall garden.

7. It improves water filtration by slowing water movement across the soil. This gives water time to soak in, especially in soils that might suffer from drainage problems.

8. Consider 'living mulches' - Australian native groundcovers. These have the added benefit of providing flowers. :) A good example is Hemiandra pungens. (This is also drought tolerant, full-sun and shade tolerant, and has the added benefit of being STUNNING):





However, with mulch, it's important to remember a few rules to make sure you're using it to its best effect:

What to know about mulch:

1. Don't apply to thinly or thickly. Too thick, and water will not be able to saturate adequately into the soil. Too thin, and you won't get adequate weed-preventing and soil-insulating benefits. A good rule of thumb is:
- Organic mulch: 7.5cm thick
- Non-organic (like scoria): 2cm thick.

The best way to test this is simply to apply the mulch, water the garden for ten minutes from above, and check how far down the water penetrated. It gives you a good idea how thick your mulch will need to be for your garden. :)

2. Only replace mulch when it has obviously decomposed into the soil. With an organic mulch type, this is usually about once every two years, and less, with subsequent applications. The reason for this is that otherwise you'll end up with layers that are too thick.

3. Avoid fine mulches of small, similarly sized particles. This means sawdust!!! Please, please don't mulch with products like sawdust, even if it's 'jarrah sawdust' and looks awesome. Sawdust can be great for pathways (it's pretty, if messy), but not really good as a mulch product. The reason being that over time, sawdust forms a thick, impenetrable mat around the plants, and literally won't allow water through without being manually broken up on a regular basis. The same applies to non-organic mulches like scoria and granitic sands. Basically, the chunkier and bigger the pieces of matter (or more variable the pieces), the more likely your mulch will happily let water through.



So not this (jarrah sawdust):





But this (coarsely ground, native wood mulch):





4. Mulches with a lot of leaf litter shed and repel water. Avoid these. Especially mulches made of eucalyptus litter. These mulches will only really be useful if they're left to compost for about a year, or if they have had their oils leached out or have been pre-composted. Basically, don't be tempted by the shire's offer of free mulch based on eucalyptus leaf litter from pruned branches. It looks like regular mulch, but it's not going to help at all. Also, eucalyptus oil is flammable...so...yeah.

5. Vary your mulch from time to time to encourage different nutrient uptake in the soils. Don't be too loyal to any one brand, basically.

6. Don't pile mulches against the trunks and bases of plants - this kills them. It promotes collar rot and fungal attacks, these weaken and can kill trees and plants. Besides, not piling up mulch around the bases of plants allows more water to penetrate near the stem.

7. Ensure that your mulch is dieback free. Die back is a fungal infection (Phytopthera cinnamomi) that kills a lot of banksias, eucalyptus and other Australian natives. Make sure you call around and look for a dieback-free mulch, your native garden will thank you for it. A lot of nurseries that specialise in selling native plants, will often specialise in providing dieback-free mulches.

8. Mulches designed for exotics usually aren't designed for natives. Yeah, this is very unfortunate. If you have a garden that is mixed exotics/natives, then you'll probably need to pick a mulch that won't be too nutrient heavy (i.e. something that is slow to break down, like bark chips).


Remember that you can always use the prunings from your own natives to contribute to the mulch along your floor. I'm an extraordinarily lazy gardener in the sense that I pretty much just let prunings fall wherever, to form part of the mulch bed. I might cut down the larger branches into smaller pieces, but nothing gets put in the bin. It's nitrogen-low mulch that will decompose over time, and while it may look a bit scrappy in the short-term, it makes the garden happier. :)

With mulch, don't be afraid to shop around, and don't always go the cheapest option. If money is an issue, you can consider buying mulch in bulk (which often drastically lowers the cost), or you can simply mulch around new plants, and mulch other areas as necessary. That said, do keep in mind that mulching natives will save money in the long-term; you'll require less fertiliser, less watering (sometimes NO watering, depending on what your species selection is like), and sometimes one healthy application is all that's needed for many years. It also prevents soil erosion, and in areas like Perth where there can be large amounts of dust and sand, stops dust and sand accumulation on windows and sliding doors.

Try to avoid using newspaper underneath mulch as a weed suppressant. A really good mulch will go a long way to deterring weeds, and newspaper attracts termites. Very thick layers can support whole colonies of termites. Don't be afraid to use your mulch in tandem with a wetting agent, so that your soil remains particularly water absorptive. Remember that no mulch is going to be 100% better than any other, so consider the requirements of your garden carefully before making a decision.
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