Dry Summer Ahead! Use Mulch
By Bob Chapman
Many parts of California are experiencing shortages of water and some forms of rationing are being implemented. This drought will affect all gardeners and we must take steps to use less water in our gardens this year. One very effective way to conserve the water applied to our garden is to prevent the loss of precious water to the drying effects of the wind and the rapid evaporation of moisture by the sun. The use of mulch will certainly keep the use of water down to a manageable level.
WHAT IS "MULCH"?
Mulch is any material, organic or inorganic, spread thickly over the surface of the soil. Here's what thick mulch will do for your garden:
- It will retain vital moisture in the soil
- Mulching the soil keeps it cool in summer and warmer in winter
- It prevents crusting of heavy soils
- Thick mulch helps prevent weeds from growing (less work for you this summer!)
- Mulch slows or prevents water from running off slopes
WHERE CAN I USE MULCH?
Mulches are usually used in shrubbery borders or under trees but not in annual flower or bulb beds. It is far more effective when spread over weed-preventing landscape fabric. Landscape fabric is a specially woven, very long-lasting poly fabric that lets water and fertilizers pass through but not sunshine. Seeds of weeds must have sunlight in order to germinate and grow and deprived of light do not germinate.
ORGANIC MULCH MATERIALS
These "Earth Friendly" materials consist of farm residues, natural materials (dead leaves, grass and other debris that has fallen to the earth) that have been composted, or surplus logging materials.
- Examples of farm residues are hay, straw, pomace, rice or cotton seed residues. Unless you have a source, farm residues are seldom seen or used.
- Chips of bark or wood, sawdust or shredded bark come from logging and mill operations and are currently the most commonly used mulches.
- Other organic materials sold for use as mulch are aged and composted manures, mushroom compost, or peat moss. Manures and mushroom compost are not often advised for use as mulch as they can contain high concentrations of salt, causing long-lasting problems in alkaline soils.
WIDELY USED MULCH MATERIALS
Bark, chips or sawdust from pine, hemlock, fir or redwood trees are the commonly used mulching materials. Some mulching materials are dyed, thus giving color to the landscape.
- Redwood bark chunks are widely used and are available in small, medium or large sizes. The bark is light brown in color when first applied and turns gray with age.
- Chips are ground-up parts of logs, usually pine, hemlock or fir. They are whitish in color when first spread, but eventually turn grayish. They range in size from 1-3 inches long and 1/2 - 1 1/2 inches wide.
- Redwood sawdust is brown at first, turning gray with age. Sawdust from pine, hemlock or fir is lighter in color, but it, too, turns gray. Sawdust can "float" in a heavy rainstorm.
- Shredded redwood bark is lighter color and is easy to spread. Some call this mulch "gorilla hair."
INORGANIC MULCHES
Pea gravel, rock, rock chips, lava rock, white rock and cobbles are widely used inorganic mulches.
- Pea gravel, rocks of various sizes and cobbles (round stones 4-8 inches in size) are used for decoration.
- Rock mulch protects oak trees from root damage and possible fungal infections. The roots are also protected from trampling. Rock mulches must be applied thick enough to afford the advantages of organic mulches in moisture retention and weed control unless landscape fabric is used underneath.
- Many gardeners use black plastic sheeting under rock mulches to prevent moisture loss and weeds from growing. Black plastic used under mulches or as mulch should be 4-6 mil strength. Wire pegs are used to hold it in place. Plastic keeps weeds out but prevents the addition of water to the soil and excludes air to the root zone. To allow air and water through the black plastic, punch large holes in the material after pegging and before covering with rock materials. Be aware that plastic eventually degrades due to weathering and exposure to ultraviolet rays. Because of this, landscape fabric was developed and wise gardeners use it instead of plastic sheeting.
HINTS AND TIPS ABOUT MULCHING
- You must kill and remove all vegetation before using mulch.
- Mulch makes the landscape look neat and tidy. You don't need to weed an area when landscape fabric is covered in thick mulch. Landscape fabric is a woven poly plastic, porous material that allows air, fertilizers and moisture to the roots but prevents weeds from growing through it.
- A thinner layer of mulch is satisfactory when spread over landscape fabric. All you need to do is to hide the fabric, keeping the direct rays of the sun from it and preventing possible degradation.
- When planting trees or shrubs in an area covered with mulch over landscape fabric, move aside the mulch, cut an "X" in the fabric, fold it back and dig the hole and plant. Keep the fabric and the mulch from contacting the trunk to prevent possible infection from root and collar rots.
- Can you put on too much organic mulch? Yes, if too deep, mulch can exclude air and moisture to the soil and plants roots. Three to four inches deep is the maximum or desired thickness.
- Does organic mulch "disappear"? Yes, organic mulches eventually break down and enter the soil as humus. Periodic replacement is needed.
- Does the humus from organic mulches help the soil? Yes, it provides food for soil organisms and creates a better growing environment for roots.
- Inorganic mulches (gravel, rock, and cobbles) add a decorative touch to the landscape. These coverings, in and of themselves, make an attractive addition to the landscape when using colored rock, smooth river rock or common pea gravel. Always place landscape fabric under these mulches. Just add enough of these mulches to hide the fabric. When children may be tempted to scatter decorative rock, consider using smooth cobbles. These are too large to be easily picked up and can't be kicked out of place.
HOW MUCH ORGANIC MULCH IS NEEDED?
Take accurate measurements of the area to be covered. Use the suggestions below for determining the quantities needed. Organic mulches can be ordered in bulk from "Bulk Express." See the friendly sales associates in our nurseries for a brochure listing items sold, a website address and phone numbers to place an order.
- For covering a hundred square feet (10'x10') 2 inches deep you will need 2/3 of a cubic yard.
- For covering a hundred square feet 3 inches deep you will need 1 cubic yard.
- For covering a hundred square feet 4 inches deep you will need 1 1/3 cubic yards.