A stand of sugar maple (Acer saccharum) trees at VanDusen Botanical Gardens, makes its own golden mulch as well as its delicious syrup.
The importance of mulch
A leaf mulch with Dutch iris, Iris reticulata.
Save time weeding, watering and fertilizing with a 3 inch layer of organic mulch laid on top of the soil around plants and any unplanted areas. Don't mix it in; just lay it on top of the soil. As it decomposes, it eventually becomes depleted over time and must be replenished annually. Ideally, it should be kept at least 3 inches deep. Anything less decomposes too quickly and is ineffective. Don’t remove the old stuff, just add the fresh mulch on top.
Think of organic mulch as a carpet or blanket that protects and nurtures the soil beneath, just like nature intended.
So what does nature have to do with anything? In meadows, forests and other natural environments, fallen leaves, twigs, bark, spent flowers, fruit and other organic debris continually fall to the ground then decompose. This process builds soil and sustains the ecosystem. Applying organic mulch is an attempt to duplicate nature's soil building process.
So why should we try to duplicate nature? With the addition of organic mulch, the soil becomes a functional, self-sustaining and biodiverse ecosystem. As it breaks down it enriches the soil. Insects, earthworms, fungi, bacteria and microorganisms feed on the mulch, and in doing so, they convert it into plant food.
I have seen the benefits of using organic mulch with my own eyes on many occasions over the years. I have run out of it a few times, resulting in partially covered beds. It was easy to see its advantages, even after a few days. Plants in the covered areas quickly responded favorably, however, ones in bare areas became wilted in the heat of the day and needed extra water to keep them happy. When I didn't get the mulch on soon enough, plant leaves yellowed and growth slowed as they ran out of food well before the mulched areas did. Weed seeds quickly found their footing in the unmulched bed, but not so in the mulched part. It was quite apparent that organic mulch makes a big difference in plant health and maintenance.
Think of organic mulch as a carpet or blanket that protects and nurtures the soil beneath, just like nature intended.
So what does nature have to do with anything? In meadows, forests and other natural environments, fallen leaves, twigs, bark, spent flowers, fruit and other organic debris continually fall to the ground then decompose. This process builds soil and sustains the ecosystem. Applying organic mulch is an attempt to duplicate nature's soil building process.
So why should we try to duplicate nature? With the addition of organic mulch, the soil becomes a functional, self-sustaining and biodiverse ecosystem. As it breaks down it enriches the soil. Insects, earthworms, fungi, bacteria and microorganisms feed on the mulch, and in doing so, they convert it into plant food.
I have seen the benefits of using organic mulch with my own eyes on many occasions over the years. I have run out of it a few times, resulting in partially covered beds. It was easy to see its advantages, even after a few days. Plants in the covered areas quickly responded favorably, however, ones in bare areas became wilted in the heat of the day and needed extra water to keep them happy. When I didn't get the mulch on soon enough, plant leaves yellowed and growth slowed as they ran out of food well before the mulched areas did. Weed seeds quickly found their footing in the unmulched bed, but not so in the mulched part. It was quite apparent that organic mulch makes a big difference in plant health and maintenance.
Why Mulch?
- Insulates and protects the soil from temperature extremes.
- Retains soil moisture and reduces soil evaporation.
- Reduces weed growth.
- Prevents erosion.
- Reduces soil-borne diseases as it prevents spores from splashing from the soil into the plants.
- Mulch decomposition contributes to soil fertility and health.
- Increases microbial activity and earthworms.
- Prevents soil crusting.
- Reduces soil compaction.
- Many types are aesthetically pleasing.
Organic Mulch Maintenance
Why would anyone want to rake this away? It looks pretty good to me.
Organic mulch eventually becomes depleted over time as it decomposes, so it must be replenished. Ideally, it should be kept at least 3 inches deep. Don’t remove the old stuff, just add the fresh mulch on top.
Topping up the mulch is generally a yearly garden chore. If you have to apply it more often to keep it 3 inches, it is probably because you didn’t lay it on thick enough initially or the pieces are just too small. The coarser the mulch the longer it takes to decompose.
Fall is a great time to top up the beds with autumn leaves as they are so plentiful. Instead of bagging and putting them curbside to be hauled away, rake them onto garden beds. Same thing goes for those leaves on the lawn: don’t toss them. Save yourself time, money and your back by mowing the leaves while they are still on the lawn. No raking needed. Dump the shredded, bagged leaves on top of garden beds.
Organic Mulches and Nitrogen Immobilization
Leaves, wood chips and other organic debris should be aged before it is used and not 'green'. Newly mown grass clippings, sawdust fresh from the lumber mill, newly pruned clippings from trees and shrubs should not be used until they have spent at least a couple of weeks decomposing in the elements.
The trouble with fresh organics is they steal nutrients and burn roots while they decay. Microorganisms, fungi and bacteria need nitrogen to decompose fresh organic material. The organisms feed on the fresh organic matter, using up the nitrogen as they go. This temporarily makes it unavailable to plants and is referred to as nitrogen immobilization. When they feed, they also produce heat, which burns plant roots causing severe damage, if not death. As soon as the process is over, everything cools right down and the nitrogen is then available to the plants to use.
So instead of discarding freshly pruned clippings and newly mowed grass speed up the aging process by placing them in a shallow pile. The pile will heat up, then cool down and shrink. Once it has cooled and settled, it's ready to use as a mulch.
But what if the deed is done, and you have already placed fresh plant material on the garden and your plants are yellow and dying? Waste no time to add nitrogen as the plants are starving. Apply a liquid nitrogen fertilizer such as fish fertilizer or another water soluble fertilizer high in nitrogen. Granular fertilizer would take too long to be effective, so stick with the liquid applications.
Inorganic Mulches
There is a certain appeal to rock mulches and they are suitable for alpine designs and rockeries, however they do have their drawbacks. Gravel, lava rock, stones, plastic, landscape fabric and rubber are other examples of inorganic mulches. Because they don’t decompose, they contribute little to the soil. Weeds will eventually grow on top of the fabric, plastic and between the rocks.
Rock Mulch
River rocks, gravel (crushed stones), pebbles, volcanic (pumice) cost more than organic varieties, but provide aesthetics that many people find attractive. They also offer permanence because they don’t decompose. They also come with a few drawbacks.
Drawback #1: Misbehaving Rocks
Gravel and pebble has the ability to travel outside of the beds and can be easily become projectiles when they come in contact with lawn mowers and line trimmers. You will also find them in your shoes and in the house if you are not careful. To help keep rock mulches in place edge rock and gravel paths. Gravel is often used for paths but it does tend to travel outside of its confines. Do place landscape fabric under the rocks so they don’t become one with the soil with the subsequent foot traffic.
Drawback #2: Difficult to Plant
Another issue I have with rock mulches is they make the simple act of planting or removing a plant an ordeal. The landscape fabric, which is often placed under inorganic mulches, makes it difficult to plant. Combine that with a whole pile of rocks overtop and planting that wee petunia becomes a time consuming and difficult process. First the rocks have to be shifted. This can be quite arduous if it is a deep layer or if they are big and heavy. Then the fabric has to be cut with a knife, followed by digging of a hole. Care must be taken to keep the soil from contaminating the rocks. Any soil left on top of the landscape fabric becomes a breeding ground for any weed seeds and it looks unsightly.
Drawback #3: Weeds Still Grow
Ironically, rock mulches are touted as a low maintenance option to halt weeds. It rarely works, even with landscape fabric underneath. Unfortunately, organic debris quickly forms between the rocks on top of the landscape fabric. Wind blows in soil, birds drop their seed laden droppings, and plants drop their leaves, seeds, petals and twigs. All this organic litter accumulates between the rocks and settles on the fabric, becoming a desirable breeding ground for weeds.
When weeds do take hold, removing them isn't easy as the rocks weigh them down. The bigger and heavier the rocks, the more difficult it is to yank them out. The displaced soil that occurs when pulling the weeds also adds to the existing debris between the rocks. Soon a layer of soil forms and even more weeds spring up making it look unsightly and it becomes a maintenance nightmare.
Drawback #4: Soil Health
Landscape fabric works well for hardscape applications such as under paths, however, it is detrimental to use on garden beds. It acts as a barrier preventing life within the soil to flourish. It does not allow soil insects, earthworms and microorganisms to come to the surface to gather and eat all that delicious organic debris that makes soil so much better. The soil food web is unable to function so plants go hungry.
Black plastic is often used as an inexpensive alternative to landscape fabric. Plastic should never be used for any reason, even under paths as it does not allow water and air to penetrate. This results in flooding and dead soil.
Inorganic Mulches: Rubber
Rubber mulches are usually made from recycled tires. They insulate soil from heat more effectively than wood mulch and allow more moisture to reach the soil compared to wood mulch, which absorbs water. Weeds and fungi are deterred as their seeds and spores do not take hold. Because it is rubber, its spongy to walk on, which offers an advantage to playgrounds, however, there are some important disadvantages. A major one is they leach chemicals toxic to plants in high concentrations into the soil. Larger pieces leach fewer chemicals, and some brands leach less than others. It is best kept away from edible plants and young or delicate plants and they do nothing to improve the soil ecology.
How to Apply Organic Mulch
- Weed area before applying the mulch.
- Do not put landscape fabric or plastic under organic mulch.
- Apply mulch to the soil surface at a depth of 3 inches.
- Maintain mulch to a 3 inch depth by topping it up annually.
- After applying, give it a good soaking to make sure it stays put.
- Avoid bark nuggets as they don't readily decompose and can ward off beneficial insects and microbes, however, they are suitable for paths.
- Avoid placing mulch against tree trunks and on top of plants due to rotting.
- Apply mulch to a new bed once big plants have been installed.
- For small plants, plant them after the mulch has been laid.
- Avoid pressure treated wood products due to toxins leaching into the soil.
- Cedar, redwood and bark nuggets are more suitable for paths and areas where soil insects are not a priority as they deter insects: avoid using them on garden beds.
- Trees benefit from being planted in their own mulched bed. An 8 foot circular bed with a 3 inch layer of mulch not only benefits the tree, it prevents line trimmers and lawn mowers from damaging the tree trunk. One caveat though; keep the mulch a few inches away from the bark so it doesn't rot.
- Avoid piling up mulch against the base of a tree, like a volcano. It promotes trunk rot and becomes a place for rodents to nest as well as providing them with nice tender tree bark to nibble on. Tree guards around the trunkare often used to protect the bark, however, they do more harm than good. They are a haven for bugs and mold and if left on, they can strangle a tree to death. It's not a nice way to go.
Types of Mulches
Leaves:
Foliage contain many nutrients and are very beneficial mulch. Collect leaves in fall and place on garden beds, avoid using black walnut (Juglans nigra) and eucalyptus leaves as they inhibit growth (allopathic) especially on edibles. Shred leaves with a lawn mower while they are still on the lawn to save time bagging and to help them decompose. Oak leaves take a while to rot down so shredding them with the lawn mower is a good idea.
Chop & Drop:
When cutting back plants, there is no need to compost or discard their remains. Just chop them and drop them on top of the soil around the mother plant. Avoid making big piles, just spread them out about an inch or two deep.
Grass Clippings:
Only use if herbicide free. Avoid thick layers of freshly cut grass as it ties up nitrogen as it decomposes. Allow newly mowed grass clippings to age by placing them in flat piles just a few inches deep.
Hay and Straw: Use straw as hay contains seeds. Decomposes quickly so spread thickly. Suitable for veggie beds and to incorporate in spring before planting. Easily blown by wind so apply thickly. Avoid fresh as it ties up nitrogen as it decomposes. Both make perfect homes for rodents, so avoid if they are a problem in your garden (or get a cat). Not aesthetically pleasing for garden beds.Pine Needles/Straw: Acidifies soils, aesthetically pleasing, slow to decompose, resists compaction, should be 3 inches deep to prevent weed growth.
Pine Needles:
Keep needles under pine trees as it is their natural mulch acidifying soil. They are slow to decompose, are aesthetically pleasing and resist compaction. Make sure it is at least 3 inches deep to prevent weed growth.
Tree Bark (nuggets and shredded):
Fir (Abies spp.), Douglas fir (Pseudotsuga menziesii) and spruce (Picea spp.) are the most common types. Good for paths, not garden beds, as resistant to insects and weathering. Excellent resistance to compaction. Decompose very slowly; not a good nutrient source. Does not absorb or release moisture as well as wood chips and recycled wood.
Wood chips and recycled wood:
Derived from hardwood (deciduous) and softwood (conifer) trees. Large chips decompose slower than small chips and shredded types. Not recommended for veggie gardens, but good for ornamental beds. Avoid walnuts (Juglans spp., cedar (Thuja spp.), eucalyptus, redwoods (Sequoiadendron spp.) As they inhibit plant growth and deter beneficial insects and microbes. Also avoid wood chips that have been chemically treated. This type of mulch encourages soil organisms, resists compaction, reduces evaporation, absorbs moisture when wet and releases moisture when dry. Make sure it is old, aged wood and not fresh as it will tie up nitrogen (nitrogen immobilization). Do not incorporate it into the soil as it also may tie up the nitrogen so just use it as a mulch.
Sawdust:
Avoid using cedar, redwood, walnuts, eucalyptus or wood that has been chemically treated. Recommended for blueberries and other acid loving plants. May tie up nitrogen especially if freshly hewn sawdust. Decomposes rapidly. Tends to compact over time.
Compost:
Provides nutrients and other goodies to the soil and plants, but does not reduce weed growth. Not as good at insulating soil, or reducing weeds as compared to woody, coarse mulches. Decomposes quickly but improves soil fertility and health when incorporated into soil.
Newspaper and Cardboard:
Made of processed wood, so it decomposes easily. Use shredded, torn or laid flat on the soil at least 1 inch deep. Wet it down as you lay it so it doesn’t blow away. Not aesthetically pleasing so place woodchips or other organic mulch overtop or use in vegetable gardens. Avoid glossy paper, magazines as they are coated in plastic. Remove any tape and staples from cardboard.
Manure
Not recommended as a mulch as it does not deter weeds or insulate soil. Use only to enrich soil by incorporating well aged manure into garden beds.
Landscape Fabric, Black Plastic
Not recommended to use as a mulch or under mulches and it prevents soil organisms to come to the surface of the soil so they cannot do their thing. Use landscape fabric under gravel paths but refrain from using black plastic as it is a soil killer as it does not allow water or air to move through soil. Neither deter weeds as they just grow on top of the fabric or plastic.
Foliage contain many nutrients and are very beneficial mulch. Collect leaves in fall and place on garden beds, avoid using black walnut (Juglans nigra) and eucalyptus leaves as they inhibit growth (allopathic) especially on edibles. Shred leaves with a lawn mower while they are still on the lawn to save time bagging and to help them decompose. Oak leaves take a while to rot down so shredding them with the lawn mower is a good idea.
Chop & Drop:
When cutting back plants, there is no need to compost or discard their remains. Just chop them and drop them on top of the soil around the mother plant. Avoid making big piles, just spread them out about an inch or two deep.
Grass Clippings:
Only use if herbicide free. Avoid thick layers of freshly cut grass as it ties up nitrogen as it decomposes. Allow newly mowed grass clippings to age by placing them in flat piles just a few inches deep.
Hay and Straw: Use straw as hay contains seeds. Decomposes quickly so spread thickly. Suitable for veggie beds and to incorporate in spring before planting. Easily blown by wind so apply thickly. Avoid fresh as it ties up nitrogen as it decomposes. Both make perfect homes for rodents, so avoid if they are a problem in your garden (or get a cat). Not aesthetically pleasing for garden beds.Pine Needles/Straw: Acidifies soils, aesthetically pleasing, slow to decompose, resists compaction, should be 3 inches deep to prevent weed growth.
Pine Needles:
Keep needles under pine trees as it is their natural mulch acidifying soil. They are slow to decompose, are aesthetically pleasing and resist compaction. Make sure it is at least 3 inches deep to prevent weed growth.
Tree Bark (nuggets and shredded):
Fir (Abies spp.), Douglas fir (Pseudotsuga menziesii) and spruce (Picea spp.) are the most common types. Good for paths, not garden beds, as resistant to insects and weathering. Excellent resistance to compaction. Decompose very slowly; not a good nutrient source. Does not absorb or release moisture as well as wood chips and recycled wood.
Wood chips and recycled wood:
Derived from hardwood (deciduous) and softwood (conifer) trees. Large chips decompose slower than small chips and shredded types. Not recommended for veggie gardens, but good for ornamental beds. Avoid walnuts (Juglans spp., cedar (Thuja spp.), eucalyptus, redwoods (Sequoiadendron spp.) As they inhibit plant growth and deter beneficial insects and microbes. Also avoid wood chips that have been chemically treated. This type of mulch encourages soil organisms, resists compaction, reduces evaporation, absorbs moisture when wet and releases moisture when dry. Make sure it is old, aged wood and not fresh as it will tie up nitrogen (nitrogen immobilization). Do not incorporate it into the soil as it also may tie up the nitrogen so just use it as a mulch.
Sawdust:
Avoid using cedar, redwood, walnuts, eucalyptus or wood that has been chemically treated. Recommended for blueberries and other acid loving plants. May tie up nitrogen especially if freshly hewn sawdust. Decomposes rapidly. Tends to compact over time.
Compost:
Provides nutrients and other goodies to the soil and plants, but does not reduce weed growth. Not as good at insulating soil, or reducing weeds as compared to woody, coarse mulches. Decomposes quickly but improves soil fertility and health when incorporated into soil.
Newspaper and Cardboard:
Made of processed wood, so it decomposes easily. Use shredded, torn or laid flat on the soil at least 1 inch deep. Wet it down as you lay it so it doesn’t blow away. Not aesthetically pleasing so place woodchips or other organic mulch overtop or use in vegetable gardens. Avoid glossy paper, magazines as they are coated in plastic. Remove any tape and staples from cardboard.
Manure
Not recommended as a mulch as it does not deter weeds or insulate soil. Use only to enrich soil by incorporating well aged manure into garden beds.
Landscape Fabric, Black Plastic
Not recommended to use as a mulch or under mulches and it prevents soil organisms to come to the surface of the soil so they cannot do their thing. Use landscape fabric under gravel paths but refrain from using black plastic as it is a soil killer as it does not allow water or air to move through soil. Neither deter weeds as they just grow on top of the fabric or plastic.
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