What Is Mulch?
Mulch is any substance that you can spread or lay on top of the soil surface. There are two types of mulch, those which add nutrients to the soil and those that don’t. Both types improve the look of your garden and smother weeds. Be careful when acquiring organic mulch as if you are not careful it is quite possible for weed seeds to be mixed in with it. Be sure you know where it comes from and if it has been composted properly. The process of composting will produce enough heat to sterilise any viable seeds.
What is it made of?
Mulch that adds nutrients are generally made from substances that decompose and add bulk and nutrients to the soil.
There are many types of organic mulch, here are just a few:
Shredded or chipped bark. Bark mulches are best used where there will be minimal digging, such as around trees, shrubs and walkways. Woody mulches do not mix well with soil and it can be a nuisance to move it to make way for planting. Bark and wood chip last longer than the other organic mulches however.
Composted organic garden waste. Composted garden waste can be used anywhere as long as the composting process has produced enough heat to sterilise any seeds. This type can be used as a general covering or as a dressing for specific plants during the growing season to feed and insulate.
Composted manure. Manure is a favourite but it must be well composted to get rid of any disease or smell. Application is like general composted garden waste. If you can find someone who keeps horses or chickens it is worth offering to take some bags of manure off their hands.
Grass cuttings. The use of grass cuttings should be reserved for areas of the garden which are well away from the populated area. They contain a lot of water, decompose rapidly and turn into a slimy mass with an unpleasant smell. They also tend to form a water impermeable mat. Ideally, if you use a mulching mower, the grass cuttings can be left on the lawn to add fertility. If not then add them to the compost heap to rot down bearing in mind that you will need to add a lot of dry organic matter such as newspaper or straw to get the proper moisture balance. Remember too that if you add chemicals to your lawn then you will not want to add composted grass cuttings to your vegetable plot.
Newspaper. Newspaper mulch is very popular especially since printers have changed over to organic printing dyes. Paper can be used as a shredded mulch to insulate plants or as paper sheets to smother weeds and retain moisture. When you lay the newspaper it is best to wet them to prevent the sheets from blowing away before placing a layer of different mulch on top. The paper should prevent weeds from germinating through the growing season. Layers of newspaper are also useful for smothering and removing grass to start a new growing bed.
Shredded leaves. Shredded leaves are nature’s mulch that is provided every autumn when the leaves fall from the trees. You can use leaves anywhere and they have the added advantage of encouraging earthworms into the area to mix the nutrients with the soil. Leaves look especially attractive around trees and shrubs and in a woodland setting. In addition if they are used as mulch in a vegetable garden in the autumn, they will have decomposed and added fertility to the soil by the spring.
Straw. Straw is popular mulch for a vegetable garden. It is traditionally used around strawberry plants (hence the name) where it prevents the berries from coming in contact with the ground and providing free food for slugs and similar pests. When used around plant in general, the straw prevents soil and certain diseases from being splashed onto the lower leaves and fruit. Straw will decompose slowly and add nutrients to the soil throughout the growing season. Straw also provides a warm and snug home for beneficial insects whose job it is to keep your veggies pest free. When the time comes to tidy up the garden and replace the mulch, it is a simple job to rake up the remaining straw or dig the remnants into the ground.
Non –organic and synthetic mulches do not supply nutrients to the soil but are very good at holding moisture, suppressing weeds and do not decompose like organic mulches. Inorganic mulches are made from any material other than plants. It does not provide nutrients to the soil, it doesn’t decompose so will not have to be renewed. It also will not provide a food source for pests and fungus.
Sand, stone & gravel. Chipped stone, sand and gravel are useful in areas that require good drainage and around plants that need a bit more warmth than usual. The main problem with using these items as mulch is that they are difficult to remove if you change your mind.
Black plastic. Black plastic sheeting is useful where plants don’t need a lot of digging and fertilisation. The plastic membrane effectively stops any light getting to the soil underneath and provides a barrier to any weeds that do decide to germinate. Make holes in the sheet so you can insert plants where you want them. Plastic tends to get hot in the summer so make sure there are enough small holes for moisture to seep through. The only problem with this mulch is that black plastic sheet is unsightly so use it below another mulch such as stone or gravel.
Landscape fabric. Landscape fabric is a good alternative to plastic sheet as it is permeable to water allowing rain to pass through. It is still a good idea to disguise the fabric with stone or gravel.
What are the advantages and disadvantages of using mulch?
The advantages of using mulch on the garden are:
- It prevents evaporation and reduces water use by up to 75%.
- As it decomposes, the mulch releases nutrients into the soil.
- It encourages earthworms to mix the mulch with the soil, aerate and fertilise the soil with wormcasts.
- A layer of mulch on top of the soil inhibits the germination of viable weed seeds.
- Certain types of mulch, for example straw, provide a home for beneficial insects.
The disadvantages of using mulch are:
- In the spring when the plants need as much warmth as they can in order to germinate, the layer of mulch can provide insulation and prevent the warmth from reaching the roots.
- A layer of mulch provides refuge for small creatures such as slugs which can cause problems with young carrots and peas.
- Unless you take great care, some vegetables cannot grow in mulched ground but require sandy, well-drained soil.
How do you lay mulch?
Laying mulch in your garden is a simple enough process but it helps if you plan the operation beforehand to get the most out of your mulch.
Choose the correct mulch for the job. Before you decide on your mulching material you must think and plan sensibly about what are the reasons for laying mulch.
- What do you want the mulch to do?
- Is it going to prevent weeds?
- Reduce water loss from the ground?
- Make the ground visually attractive?
- How available is your chosen mulch?
- Can you use a by-product of your garden such as grass cuttings or leaves?
- Or will you have to buy something such as stone or plastic sheet?
If you use a plastic sheet, it will not only prevent weeds but will also make watering difficult. Do you want the mulch to disintegrate over time and become part of the soil or do you intend to leave it there long term? If so use stone or plastic. Is the mulch planned to be a visual feature in its own right or are you intending it to only cover the planting beds during the winter without worrying what it looks like?
Prepare the area to be mulched. Don’t forget that once you have put down a layer of mulch, you don’t want to be moving it again for quite some time.
- Prepare the ground underneath.
- Pull out any weeds or cut them down close to the ground.
- Enrich the soil and dig the beds.
- Although mulch will degrade and leach nutrients into the ground this will take time and you don’t want your plant to starve while they are waiting.
- Depending on the purpose of the mulch you can add layers of plastic sheet, landscaping fabric, cardboard or newspaper.
- Then mark out the edges of the area.
- Beg, swap or buy your mulch.
- Ask around in your neighbourhood as to whether anyone has some piles of leaves or compost they want to get rid of.
- Maybe you know someone who keeps horses or chickens. If so, and they don’t want the manure for their own garden you can ask if you can have it.
If you can’t beg or swap some mulch then you will have to buy some. Garden or home improvement centres with a nursery section will sell different kinds of mulch in manageable bags that will fit into the back of your car. They may even sell it in bulk and deliver on a truck.
Look in your local newspaper for adverts from truck owners offering to deliver gravel or chipped stone.
Many tree services or landscape gardeners will be very pleased to offload shredded tree chippings for you as they will have to pay to get rid of their waste.
Transport it home and place it where it is needed. After you have transported it home either by the bag or in bulk, use a wheelbarrow or a bucket to carry the mulch to the prepared area of ground.
Lay the mulch. The thickness of the mulch is very important if your purpose is to prevent weeds and retain moisture in the ground. Preferably have at least two to four inches (50 to 100 mm). If the purpose is purely visual and you are laying stone over plastic sheet then you will need to lay enough to disguise the sheet. You will find that the optimum depth is once again at least 2 inches. When you lay the mulch, leave a small gap of about four to six inches (100 to 150 mm) around the plant or tree stems to help prevent waterlogging.
Spread the mulch. Using a garden rake level out the mulch and break up any large lumps.
Planting something new. If you need to plant anything new in your garden you will have to scrape the mulch away from the planned location and dig a hole. If you have a fabric or plastic sheet then you must cut a hole using a pair of scissors to allow access to the underlying soil.
How do I stop weeds from growing through the mulch?
The best way to stop weeds from growing through the mulch is to stop any sunlight from reaching the weed seeds. Use either a plastic sheet or landscape fabric before overlaying it with the visually attractive mulch, or use some sheets of cardboard or newspaper for a cheap biodegradable light barrier under the organic mulch. Remember to keep on replenishing the organic mulch as it will gradually become mixed with the soil by the action of earthworms and the weather.
What is the best mulch to use
Generally the best type of mulch is organic mulch. Use these if you can because it decomposes and feeds your garden plants. If you use composted material, the mulch will decompose quickly but will feed the soil and you will have to replenish it regularly.
If you use partially decomposed wood products such as bark or chips, it will continue to decompose slowly but won’t feed the soil like compost. Wood products take a long time to decompose completely so you won’t be replenishing it too quickly. Use this type around trees and shrubs.
Stone mulches are good for stabilising garden areas that are vulnerable to water movement such as on slopes, hills and around wastewater downpipes. Of course stone will improve the appearance of any garden and will tend to compact into the earth rather than mingle with it; this is useful for making paths and removing muddy waterlogged areas.
Are there different colours of mulch?
Stone mulches have the differing natural tones of various types of stone or there are the man-made stone mulches which can be sold already dyed to almost any colour you like. You can also buy tumble smoothed coloured glass mulches which add a touch of class to your garden.
Organic mulches can also be bought using vegetable dyes to add interest and contrast to your garden. Over time the dye will leach out of the mulch from weather action or be bleached by sunlight so after about a year, the colour will be something like a uniform grey and will need to be replaced.
What kind of mulch is safe for pets?
Some mulches are toxic to animals especially dogs who, by their nature, will chew anything. Cats on the other hand will not chew or eat unknown things for the sake of it so the only problem you might have is that they use the mulch as a litter box.
Mulch made from cocoa shells, also known as cocoa bean mulch is highly toxic to dogs so keep clear of it and choose an alternative such as cedar, pine or hemlock mulch.
Does organic mulch attract insects?
Mulch is a very good way of controlling weeds without chemicals but it can also provide the ideal environment for insects to live, breed and feed. If organic mulch is placed too close to the house it will provide an easy way for unwanted pests to gain access to your home. Termites, ants, sow bugs, millipedes, centipedes and earwigs are all attracted to the warm fertile food-store you have provided for them. Not only insects but rats also find the tasty manure irresistible. Always leave at least six inches (150 mm) around your house free from organic mulch, use gravel or stone instead.
Slope the ground away from the house so rain doesn’t wash the nutrients towards your foundations.
How long does it take for mulch to break down?
This depends on the type of mulch you use. Fresh woodchip will probably need replacing every 1 to 2 years. Compost and manure will decompose in a few weeks or months. Gravel and crushed rock will take years before the appearance is affected.
Mulch Delivery. A Scam?
A guy turns up at your doorstep with a truck saying he can lay down some mulch. You think “that’s great, just what I need.” He offloads the mulch in bags or even lays it around your trees (often too close to the tree trunk) and then gives you a bill for lots more that his estimated price. He says that he needed to lay more than he thought. You then negotiate a lower price which still works out more than you originally intended and the guy drives away happy with you thinking you have been conned.
You own some land and need the soil mulched. A guy with a truck shows up and deposits a load of wood chips and sawdust to “improve the soil”. Unknown to you the sawdust used to be old pallets, laminated chipboard, painted wood and other such wood waste that has been previously steeped in preservative and other chemicals to stop it from rotting. The chemicals contain heavy metal compounds used in timber preservatives such as copper, arsenic, creosote, metal paint pigments. Sometimes it contains metal, asbestos and glass fragments from demolished buildings.
These undesirable substances then soak into your ground and actually end up poisoning the soil rather than improving it. And you have paid for it too! Farmers and landowners could be breaking environmental legislation or fire regulations and if caught will not only be fined but also have to pay for the illegal waste to be removed.
In many countries good quality waste wood is useful as farmyard mulch such as livestock bedding, horse exercising areas and field entrances. There is a specific waste exemption that covers such waste and can be registered with the appropriate government agency free of charge. However you must know where the waste has come from and it must NOT be treated wood or plant waste. You must also only use as much mulch as is needed to satisfactorily do the job. If more than is reasonable is applied then this can be classed as disposal of waste.
If someone approaches you and asks if you want a load of mulch,
- Take their name and address and vehicle details.
- Ask where the waste is coming from.
- Don’t agree to pay any money or accept the mulch until you have made some checks.
- Tell the supplier that you will be informing the Environment Agency or the equivalent government body in your country.
- Have a quick visual inspection and see if you can see any traces of chipboard, plastics or metals mixed in with the woodchips.
- Either buy your mulch from a garden centre or home improvement store or contact a qualified landscape gardener.
Garden centres and home improvement stores will sell different types of mulch by the bag or in bulk. The bags will fit into the back of your car but the bulk mulch will have to be delivered by truck. The most common size of mulch bag in the USA is 2 cubic feet whereas bulk mulch sells by the cubic yard. In the UK the usual size bag is 10 litres or 25kg and the bulk size is sold in cubic metres.
Waste Wood Mulch
|Type – Bulk wood chip||Unit||Price
|Black Hardwood||1 cubic yard||$65
|2 to 5 cubic yards||$46
|6 to 11 cubic yards||$40
|Coloured||1 cubic yard||$33
|Dark brown fines||1 cubic yard||$35
|Double shredded log||1 cubic yard||$25
|Hardwood Oak Bark||1 cubic yard||$60
|2 to 5 cubic yards||$45
|6 to 11 cubic yards||$33
|Natural||1 cubic yard||$19
|Natural fines||1 cubic yard||$16
|Shredded log||1 cubic yard||$19
Obviously the price of bulk mulch will be cheaper than buying it per bag, but you may have no choice depending on where you are buying it from.
Organic mulch is made from any type of plant material and can include manure and compost.
Pine bark & needles. This type of mulch will help plants absorb and retain moisture. It is very light and easily blows away so don’t use it if you are subject to strong winds.
Straw & Hay. You can buy this from a local farmer and is easily transportable. It readily decomposes so will need replacing annually. This also will blow away if subjected to strong winds.
Wood chip & nuggets. You can buy these by the bag at local garden nurseries and home improvement stores. Remember that wood chip will attract insects, not all of them beneficial. It may also be prone to fungal growth in wet conditions which may transfer to your plants.
Garden waste. Re-use leaves, grass clippings and compost.
|Type- Organic vegetable matter||Unit||Price
|Pine bark & needles||2 cubic feet||$12
|Straw & hay||Per bale||$5
|Wood chips & nuggets||2 cubic feet||$12
Gravel & crushed stone. There are many types of stone available, all with their own colour and texture such as gravel, cobbles, crushed slate, sand, marble and tumbled glass. The price will depend on the availability of your chosen type. Used with a sheet material to improve the look, or on its own to allow moisture to penetrate to the soil and discourage weeds.
Rubber mulch. This is softer to fall on than stone in children’s play areas and available in many colours and sizes; often referred to as playground rubber mulch.
|Type- Inorganic mulch||Unit||Price
|Landscape cloth||Per roll||$20
|Plastic sheet||15 x 3 foot roll||$30
|Gravel & crushed stone||50 pound bags||$10
|Rubber mulch||2 cubic foot||$12
All mulches come in bags or as a bulk mulch. A typical bag will cover about two cubic feet while a minimum bulk mulch delivery will be about 2 cubic yards and will cost between $350 and $700 a load. This amount should cover an area of about 110 square feet to a depth of about 6 inches.
How much mulch do I need?
The optimum depth of compost mulch is between 4 to 6 inches (10 to 15cm) to stop weeds from growing through. For feeding vegetable or flower gardens use up to 3 inches (7.5cm) and mix into the soil. For winter time mulching spread about 4 inches (10cm) to protect the soil and winter crops.
Remember that if you lay mulch deeper than 6 inches (15cm) you run the risk of stopping any warmth from reaching the plant roots and hindering plant growth by cutting out light.
To cover a garden of 1m by 1m to a depth of 15cm (3 feet by 3 feet by 6 inches) you will need about 150 litres or 0.15 cubic yards of compost or mulch.
As a general rule, you will need about
- 1 bulk bag (1 cubic metre or 1 cubic yard) for a small city garden.
- 2 bulk bags (2 cubic metres or 2 cubic yards) for an average garden.
- 3 bulk bags (3 cubic metres or 3 cubic yards) for a large garden with vegetable plot.
Something to remember is that soil, mulch and compost will always settle over time and will blend into the existing soil as it decomposes and is mixed by earthworms. So the depth of mulch is always a bit of a guess. Don’t worry about using a tape measure to get the correct depth, just have a look and if it seems about right then it probably is about right!
How do I make my own mulch?
Decide what you need the mulch for. Leaves, hedge cuttings, grass cuttings and compost make good mulch for the summer months when you want mainly nutrients and to get rid of weeds. Whereas straw, bark and pine needles are good for the winter.
The secret to making good compost mulch is to keep the amount of carbon and nitrogen in the constituents at the correct ratio. For a perfect compost heap you will need a ratio of about 25 to 30 parts carbon to 1 part of nitrogen. If there is too much carbon then the decomposition slows down and may stop and if there is too much nitrogen then you will end up with a stinky mess. In practice this can be thought of as 2 parts green material to 1 part brown material.
The Green material (nitrogen rich) and Brown material (carbon rich) are shown in the table.
|Green (Nitrogen rich)||Brown (Carbon rich)
|Food & vegetable scraps||Straw and Hay
|Garden waste||Shredded newspaper
DIY or Professional
So far we have really only talked about you choosing, laying and maintaining your chosen mulch. As it is one of the normal garden tasks needing to be done, it falls very easily into the DIY job list. It doesn’t really need any special qualifications and as long as you enjoy gardening then the job should not be too difficult. There will be garden owners however who would rather leave this task up to a professional.
Whether the professional is a qualified gardener or landscape architect who has learned the theory at college or is just the old man who enjoys gardening and has a lifetime of experience, it is important that the task is done correctly. Go to your local library or look online to find out the correct way of laying mulch. Contact your local gardening club for advice. There are plenty of sources available and you will need to know how to do the job, even if someone else is doing the manual work.
Always think of the purpose of your mulch. Whether it is needed to stop weeds, look good, feed your plants or just to save you the trouble of gardening. Go to a garden centre and see what different types are available. You never know there might be some ideas you hadn’t thought of. Always take the trouble to find out where the mulch came from. If it is reputable garden centre then there shouldn’t be a problem, however if it’s a man with a truck then alarm bells should ring. Lay your mulch properly to the correct depth and remember to not put organic mulch tight up against your house or tree trunks, use stone mulch at least 6 inches wide. Remember to regularly inspect your mulch for weeds poking through and pull them out before they get too established. Remember to replenish the mulch when it starts to look scruffy. Last but not least, no matter what type of mulch you choose, enjoy it and enjoy your garden.