Mulching: A Complete Guide

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Everything You Ever Wanted To Know About Mulching

As any gardener worth his or her salt will know, mulching is paramount to success in the garden.

Mulching is the best way to keep your soil healthy and moist all year round, whilst also helping to prevent weeds, cool roots, and prevent water evaporation.

A thorough commitment to year-round mulching might sound like a chore, but in truth it’s a time (and life) saver for serious and casual gardeners alike.

In this guide, we will cover:


Table of Contents

What is Mulching?

Why Should I Mulch?

When Should I Mulch?

Which Mulch?

Inorganic Mulches

Organic Mulches

Bark Mulches
Leaf Mulches
Compost Mulches
Grass Clippings
Pea Straw
Mushroom Compost
Horse Manure

How Much Mulch?

How to Spread Mulch

Mulch FAQs

What is Mulching?

mulch-1Mulch is a protective layer of material that sits on top of your soil to provide insulation from dryness, keep the soil warm (or cool in the summer), suppress weeds, and add nutrients that nourish your plants, trees and soil.

By providing a barrier between the soil and the air, mulch also keeps out unwanted insects, birds and animals, while conserving moisture.

Why Should I Mulch?

Aside from giving your plants a nutrient boost, retaining soil moisture and helping control soil temperature, mulching also helps cut down on garden maintenance time for you (less watering and weeding!)  With global warming, it will become increasingly important to save water, as we begin to see less rainfall – particularly over the summer months – so getting on top of your mulching schedule will not only help your own garden and plants, it will help the larger environment too.

Bark Mulch

Mulch also looks great.  A beautiful mulch covering over your borders or around trees looks fabulous as a feature, helps your plants stand out, and can even add value to your garden and property.

When Should I Mulch?

Mulch can and usually should be applied all year round (with some exceptions).


  • Winter mulching protects plant roots from low temperatures, whilst also mitigating against soil erosion and compaction from heavy rains.  If you wait until the weather starts to warm in Spring before mulching, plants will grow through the mulch and then have to compete for nutrients with the newly emerging weed seedlings.  Preventing your soil from fluctuations in soil temperature is a year round benefit of mulching, especially in a ‘4 seasons in 1 day’ climate such as New Zealand.
  • When Spring comes around, you’re going to be grateful to your mulch for preventing too many weeds from creeping through, whilst a great organic mulch encourages earthworms to take up residence in your soils, which contributes to a healthy ecosystem and benefits your plants.
  • Summer mulching is all about weed control and ensuring that your soil does not become too warm and dry out.
  • Autumnal mulching is again crucial to soil erosion avoidance, and to help perennials stay healthy and survive the winter.

Which mulch? A quick run-down of the different types of mulch.

When it comes to mulching, there’s a lot of choice out there, and picking the right mulch for your project can be overwhelming. 

Mulches can be broken down into two main categories: organic mulches and inorganic mulches.

Inorganic Mulches

Plastic MulchUsing non-natural mulching techniques including plastic sheeting, rubber and landscape fabrics is (in our opinion) a false economy.  Over time, these solutions will degrade and in some cases pollute and irreparably damage your garden.

Additionally, inorganic mulching doesn’t add nutrients to or nourish your soils, plants and trees: in fact, most ‘inorganic mulch’ solutions are essentially just weed suppression.  From a purist perspective, they probably don’t even count as mulching!

Organic Mulches

Organic mulches, as the name suggests, are comprised of natural, biodegradable material: typically compost, leaves, horse manure, rich bark or grass clippings.  Some food waste can also be used to make up a mulch.  Let’s look at some specific organic mulch types.

Bark Mulches

Bark is very effective at keeping weeds under control and retains moisture well.

Mega Bark

The great thing about bark mulch products is that they are long-lasting, break down slowly, and are great for improving drainage and moisture retention.

At Composting New Zealand, we stock a wide range of aesthetically beautiful bark mulch products including our Bark Mulch, Light Wood Mulch and Arborist Chip.  We also stock our ultra affordable Value Mulch, which is a mixture of aged bark fines and finer pieces of bark mulch (making it great for putting around new plants or trees).

Leaf Mulches

Simply collect your fallen leaves in the autumn, store in bags, and redistribute as mulch when it has turned to mush.


Leaves aren’t packed with nutrients but do make for a good soil conditioner and can be particularly useful if you’re growing fruit bushes, as they create a nice layer between the tree trunk and the fruit. Leaf mulch is also good for vegetable growers who want to encourage root growth.

It’s necessary to think ahead and be well-prepared for the following season if you wish to mulch with leaves.

Compost Mulches

Compost works great as a mulch, improving soils and aiding moisture retention.


If you wish to make your own compost at home, add organic kitchen waste such as vegetables and fruit peelings to well chopped garden waste in your home composting bin and make sure to turn every few months.

It will take around 6 months to produce usable compost for mulching, so for those not minded to compost at home, we recommend our Bio-Gro certified commercially produced organic compost.

As explored in fine detail in this blog post, we’ve got our commercial composting process down to a fine art.

Grass Clippings

Whilst well-composted home garden waste is preferable in most circumstances (and our commercial organic compost an even better option), fresh grass clippings can also be used as a lightweight mulch.  Grass clippings are rich in nitrogen and potassium which means they are a great choice for use around veggie gardens.

Vegetable plants can struggle with heavy, wet soil, hence grass clippings make for a nice light-weight mulch.

Pea Straw

Pea Straw-baleStraw is an exceptional mulch to use with vegetable and fruit plants, as it is clean, light and breaks down easily. Some straw mulches may be mixed with hay, so it’s important to source weed-free straw such as our competitively priced pea or barley straw.

Straw mulch around strawberry plants not only looks fantastic but also aids moisture retention and thwarts weeds.

Mushroom Compost

Mushroom CompostMushroom compost is an alkaline mulch with a high pH, making it ideal for use around vegetables such as kale, cabbage, and broccoli.

Essentially a leftover compost from mushroom farming, mushroom compost can lighten heavy soils, but it’s important to be selective when using mushroom compost as many acid-loving plants including berry plants and many flowers need soil with a lower pH range than that which mushroom compost will cultivate.  Also beware using non-organic mushroom compost, as you may inadvertently introduce unwanted chemicals to your soil.

Horse Manure

horse-manureHorse manure is really more of a fertiliser for your plants, and should only be used once the manure has aged and dried, otherwise it may burn the roots of your plants.  Additionally, some horse manure will inevitably contain weed seeds that have been digested by the horse.

To use as an added fertiliser agent, work methodically into your soil around the base of each plant, about 1/2 to 2 inches deep. Be careful not to overd

To help you choose the right mulch when shopping with Composting New Zealand, we’ve developed a brief quiz to help you choose the right product.

How much mulch do I need?

Volume is critical to successful mulching.

if you put too much mulch on top of your soil, it could suffocate your plants as well as weeds, whereas too thin a layer will not provide enough protection against heat, drought, pests, and diseases. You should apply about 2–4 inches of mulch depending on the season, and the particular mulch product you have chosen to use.

To calculate how much mulch you will need, start by multiplying the length and width of the area you will be covering, to give you the square footage.

Next, make a judgement call on how deep you will lay your mulch based on the type of mulch you will use and the time of year you are laying your mulch.

Around trees and in shrub beds, 3 – 4 inches of bark mulch would be a prudent application during autumn, winter and springtime, whereas less (around 2 inches) would be advisable for veggies and flower gardens.  If you are using straw mulch around your vegetable and berry plants, less will suffice.

Once you’ve made your decision, simply multiply your square footage from earlier by your chosen depth (2 – 4 inches) to give you the volumetric cubic metres required.


It’s often a good idea to use different types of mulch for different plants, trees or use cases


On the product pages for all of our mulches, we include a handy calculator to help you work out just how much mulch you will need.

How to spread your mulch like a boss!

wheelbarrow full of mulch

The key to applying mulch to your garden is to be methodical.

  1. Water.  If the weather has been dry, make sure you water your soil before laying your chosen mulch.
  2. Weed control.   Ensure that you have either weeded thoroughly, or sprayed weeds with a natural weed control agent prior to mulching.  This is essential because weed seeds may germinate during the process.
  3. Outline. Use a trowel or shovel to mark out the area for mulching.
  4. Fertilise. Mix in one of our organic fertiliser products to your chosen mulch, prior to laying.  Adding fertiliser ensures that your soil retains requisite nitrogen levels and helps stabilise the mulch.
  5. Take your time.  Adding too much mulch all at once can suffocate your plants.  It’s important to add in small, fine quantities and build up an even thickness of laid mulch appropriate to the season you’re laying it (less in summer: around 2 – 3 inches will suffice during the summer, but you should build to a thickness of around 4 or 5 inches during winter).
  6. Mulch, mulch, mulch.  Make sure to cover all areas of your garden: plants, trees, flower beds, vegetable gardens, etc – and use a rake to ensure an even covering.
  7. Replenish.  The key to good mulching is to regularly rinse and repeat. Mulch breaks down over time as your soil, trees and plants absorb the nutrients aided by worms, so it’s important to top-up regularly to reap the benefits.

Mulch FAQs

Do I really need to mulch in summer?

Soil exposed to harsh sunlight will dry out faster than soil under shade, so you will need to water more often, which in itself can lead to problems including poor root growth, drought stress and disease.

Keeping your soil well covered and hydrated is crucial.  Cover your soil with your choice of mulch (compost, straw, leaves, bark, etc) to help moderate soil temperature, prevent runoff and evaporation, and hold moisture for longer periods between waterings.

If you wish to grow plants in an open environment, it’s important to keep the soil moist but not wet. Watering too deeply can cause roots to rot and your plants to  die.  When watering, only water until the surface of the soil is damp rather than soaking the whole bed.  It’s also advisable to apply an organic fertiliser once every two weeks during growing season.

Which mulch is best, where?

The first thing to consider when choosing which type of organic mulch to use, is whether you’re applying it to a lawn or a garden.

For vegetable gardens and soft fruits, pea straw is often favoured as it suppresses weeds easily, is high in nitrogen and is simple to reapply following harvest.  A compost based mulch is a good option for some veggies and for growing tomatoes, however.

Similarly, organic compost is great for flower gardens, although you can top off with leaf or bark mulch as an effective weed suppressant.

Around trees, including fruit trees, a number of mulches will likely work well.  Leaf mulch from other deciduous trees or a good bark mulch would be an appropriate choice.

Finally, consider your soil conditions when selecting your mulch. Vegetable plants struggle with wet and heavy soil, so it’s best to avoid thick, moisture-retentive mulch. On the other hand, dry and sandy soil requires mulch that will encourage moisture to seep through.

To help you choose the right mulch when shopping with Composting New Zealand, check out the quiz further up on this guide to help you choose the right product.

What type of plants are suitable for mulching?

While most garden plants, trees and bushes benefit from mulching, there are some that should never be mulched (typically those plants that thrive in alkaline soils with a higher pH level).

For everything else – mulch away!

Shrubs love mulch because they get extra protection from wind, pests and diseases.

Herbaceous perennials like Sedum, Salvia, Lavender, Rosemary, Oregano, Basil, Thyme, Sage, Calendula, Marigold, Lemon Balm, Daphne, Impatiens, Phlox, Geranium, Echinacea, and many others all benefit from being mulched.

Many herbs benefit from mulching. Thyme loves to be mulched because it prevents root rot. If you have problems with thistle or dandelion weed, try adding a little bit of lime to your soil.

Calendula loves to be mulched, as it provides good bug protection.

Ferns love to be mulched, especially during their dormant season. Ferns don’t require much water once they have established themselves, which means less watering to worry about, although it’s important to keep them well watered during the summer months.

Carnivorous Plants & Potted Plants including Venus Flytrap, Nepeta, Crocosmia, and Amaryllis all enjoy having mulch around them. These plants rely on insects, birds and mice for food. Keeping these critters happy by providing a layer of mulch helps keep them healthy and happy.

Other house plants including Peace Lily, African Violets, Ficus Benjamina, Dracaena Deodara, and Hibiscus benefit from mulch as it protects against sunburn, prevents any pest infestations and keeps their roots cool.

I'm not getting great results: what am I doing wrong?

This is a tricky one.  Perhaps nothing! 

We’d recommend testing your soil’s pH first and foremost.  If you live in a coastal region such as Kapiti, your soil may be very loamy, and struggle to sustain the type of plants you are looking to grow.  That’s not to say that you can’t treat your soil, or replenish your soil to improve its quality.

Where bulbs or herbaceous plants are struggling to grow, it’s possible that mulch has been applied too thickly.  Use a rake to thin out the mulch and if you’ve added manure to your mulch, ensure it is nicely broken down. 

Manure that hasn’t rotted sufficiently, can sometimes scorch plant leaves, and is another common mulching mistake.

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Happy mulching!