[from Extension Notes – Ontario LandOwner Resource Centre with support from Ontario Ministry of Natural Resources – DOWNLOAD PDF VERSION]
Mulches are an effective alternative to herbicides for protecting tree seedlings from competition with other plants for light, nutrients and moisture. Placed on the soil around the base of a tree seedling, they improve growth and survival by preventing other plants from germinating or growing.
Depending on their structure and the material they are made of, some mulches also help seedlings grow by increasing the temperature of the soil and holding that heat during cool evenings. These mulches can also protect plants from extreme hot and cold temperatures.
All mulches protect plants from dry conditions by trapping moisture beneath them. The most effective of these mulches also allow air to reach the soil so that excess water can evaporate. This Extension Note provides information about the kinds of mulches that are available and how to use them effectively.
UNCONSOLIDATED AND CONSOLIDATED MULCHES
There are two basic kinds of mulches — unconsolidated and consolidated.
Unconsolidated mulches are loose materials such as wood chips, bark and straw. Although these traditional mulches have been used for centuries to control weed competition, weeds often grow through or on them. The soil temperature is also cooler under loose materials, and they do not protect plants from extreme hot or cold temperatures.
Consolidated mulches are sheets of plastic or natural fibres that are laid on the ground and anchored with staples. They are more effective than traditional mulches in preventing the germination of plants that would compete with seedlings, and many are lighter and easier to apply. Plastic mulches have the added advantage of increasing and maintaining soil temperature. Many consolidated sheets are also designed to both retain water and allow excess water to evaporate.
FACTORS TO CONSIDER WHEN CHOOSING A MULCH
Mulches should cover a minimum area of 90 x 90 centimetres around a tree.
Mulches should last until tree seedlings grow taller than the surrounding weeds — about three years for most tree species in southern Ontario. To reduce litter, plastic mulches should break down in sunlight and natural mulches should decay over this period.
EASE OF APPLICATION
Mulches should be easy to carry and quick to apply.
Ideally, they should be applied when trees are first planted.
Mulches are generally more expensive than herbicides. For example, three consecutive annual applications of the herbicide glyphosate cost in total about $0.45 a tree (materials and labor), compared to $0.74 a tree for the 90-centimetre Brush Blanket (materials only).
Types of Mulches
The Brush Blanket is a consolidated mulch made of porous plastic. It prevents weeds from germinating by blocking sunlight. This mulch improves conditions for seedling growth by increasing and maintaining soil temperature. It also allows water to reach the soil and
excess water to evaporate.
To apply, place the hole in the centre of the Brush Blanket over the tree seedling. If the hole is too small to fit over the seedling, enlarge the hole by tearing the perforated slit (Figure 1, diagram B). To reduce weed growth, use the smallest hole possible.
Pin the mulch to the ground with five staples. Insert the first staple in the centre of the mulch, then pull the corners tight and pin them down. Push the staple through the mulch and then slightly squeeze the staple ends together while inserting them firmly into the ground. The
staples should be pushed into the mineral soil — the soil below the top layer of loose organic material. Rocks and sticks can be used to hold the sheet down along the edges. Don’t use clumps of soil for this purpose.
Cellu Fib is a consolidated mulch made of recycled paper coated with wax. This mulch prevents weeds from germinating by blocking sunlight. It does not increase or maintain soil temperature.
To apply, fold the corners over and pin the corners to the ground with staples. Push the staple through the folded corner and then slightly squeeze the staple ends together while inserting firmly into the ground. To prevent weed growth in areas where weeds are a severe problem, staple a small piece of Cellu Fib over the slit.
Cellu Fib is not recommended for windy, exposed sites because the paper tears easily.
Pieces of old carpet make an effective and inexpensive mulch. They prevent weed growth by blocking sunlight and improve growth by maintaining soil moisture. They do not increase soil temperature. Old carpet can often be obtained at no cost from local waste disposal sites.
Cut the pieces with a utility knife to at least 90 x 90 centimetres. Cut a slit for the centre opening, as in Figure 1, diagram C. Place the carpet upside down around the tree.
Newspapers are an unconsolidated mulch. They prevent weed growth by blocking sunlight. Newspapers improve conditions for growth by maintaining soil moisture, but they do not increase soil temperature.
Newspapers are inexpensive and can often be obtained at no cost from recycling centres.
To apply, lay four sets of 10 to 16 overlapping sheets on the ground. Use debris or clumps of soil from the site to hold the newspapers down. Wet the newspapers so that they stick to the ground, or apply them when it is raining. Once wetted, newspapers won’t easily blow away. It is
easier to apply newspapers on rainy days. Newspapers are difficult to apply on windy days.
Newspapers last one or two seasons. For best results, they should be replenished every year.
Wood chips are an unconsolidated mulch. They prevent weed growth by blocking sunlight. They are one of the most popular mulches, and can sometimes be obtained at no cost. However, they do not improve growing conditions by raising or maintaining soil temperature. In fact, the soil temperature is generally cooler under a wood chip mulch than with no mulch at all. Wood chips improve growing conditions for seedlings by maintaining soil moisture.
To apply, lay wood chips to a depth of five to 10 centimetres over an area extending at least 50 centimetres from a tree. To reduce damage from mice and other rodents, keep the chips about 10 centimetres from the base of the tree.
If weed growth occurs, add more chips. However, do not exceed a depth of 10 centimetres. A deeper wood chip mulch will reduce root development and the amount of air getting to the soil.
When wood chips are used on soils that are low in nutrients, watch for pale, yellow-green leaves or needles on your seedlings — a sign of nitrogen deficiency caused by micro-organisms that decompose wood chips. If this occurs, treat the seedlings with a nitrogen-rich fertilizer or use a consolidated mulch.
Fresh wood chips should not be used until they have been allowed to age for six weeks.
TIPS FOR MULCH APPLICATION
- Mow weeds before the trees are planted to suppress growth and to reduce habitat for mice and other rodents that might feed on the seedling.
- Ensure that the mulch covers a minimum area of 90 x 90 centimetres around the tree.
- Apply mulches early in the spring, immediately after seedlings are planted.
- Follow the manufacturer’s instructions for fastening mulches to the ground.
- Before laying a mulch, clear away debris.
- Lay consolidated mulches as flat as possible on the ground.
- Inspect your trees every few months. Replace torn and ripped mulches. Replace newspaper mulches every year. Replenish wood chips to the correct depth, when required.
The effectiveness of mulches as tools for reestablishing forests on abandoned agricultural land in southern Ontario is being evaluated by the Ministry of Natural Resources at test sites near Ridgetown, Cayuga, Midhurst, Prescott and Almonte. The field trials are being conducted through the Vegetation Management Alternatives Program and the Sustainable Forestry
Initiative, which are developing safe and effective alternatives to herbicide spraying. Research has already shown that seedlings treated with Brush Blanket mulches grow as well as seedlings treated with the herbicide glyphosate and better than seedlings that received no weed control.
To view tree shelters, demonstration sites are located near the MNR’s Chatham, Fonthill, Midhurs and Kemptville office. Please call the office nearest you.
For more information contact:
LandOwner Resource Centre
P.O. Box 599, 5524 Dickinson Street
Manotick, Ontario K4M 1A5
Tel 613 692 2390 or 1 800 387 5304
Fax 613 692 2806
Product Ordering: 1 888 571 INFO (4636)