The one true path
Publication Date: Friday Jul 8, 1994

The one true path

Decomposed granite pathways require proper installation

by Scott Loosley

QI am landscaping my yard, including new pathways. I have seen paths constructed of crushed rock and like their appearance. Where can I find this product and how do I install it? AThe material you are referring to is known as decomposed granite, or track fines. This paving material is popular for use as an informal path and is relatively easy to install and maintain. The benefits of decomposed granite include low installation cost, "soft" appearance and good porosity that allows water to penetrate through to the soil below. This is especially important when paving near older native trees such as oaks.

Before deciding on decomposed granite as a paving surface, consider some of the drawbacks. If you have hardwood floors, you will want to leave your shoes at the door because decomposed granite acts like sandpaper, especially in wet weather. When kept constantly wet or if puddling occurs, decomposed granite can turn to soup, and paths on hillsides are prone to erosion.

Other than these situations, decomposed granite is a suitable surface. Decomposed granite is available in gray and gold and can be purchased from landscape materials suppliers. Look under the heading "topsoil" in the Yellow Pages.

Decomposed granite is not hard to install, but there is a trick to installing it properly for a solid, lasting surface. You must know some basic carpentry skills and have access to water and a roller or compactor.

First, lay out the location of your path. To contain the decomposed granite, you must install header boards along the edge of your pathway. I recommend that the lumber for the header be no less than two inches wide and four inches deep in dimension. The wood should be redwood or pressure treated for use in the ground. This may be in the form of a two-by-fours for straight runs or laminated one-by-four or four-ply bender board for curved runs.

Excavate soil in the layout of the header board to a depth of one inch. This provides for the decomposed granite to be three inches deep for the path surface (one inch of soil, three inches of decomposed granite).

Install your header boards, anchoring them with stakes about every four feet. The header boards will probably be the toughest part of the project. When you've finished with them, give yourself a pat on the back, or better yet a massage. But don't relax too much. You're only halfway through the project.

The next step is to estimate how much decomposed granite you will need to fill the area between the header boards. To make this easy on yourself, have a calculator available and a pencil and paper. Measure the length and width of your paths and multiply these two numbers together. This will give you the square footage of your paths.

Take the square footage and divide by four. The answer will give you the cubic feet of decomposed granite needed to fill the pathway to a depth of three inches.

Unfortunately, materials are not sold by the cubic foot so you will have to divide the cubic feet by 27 to come up with the number of cubic yards of decomposed granite to do the job (27 cubic feet equals one cubic yard).

Decide which color of decomposed granite you would like to use and place your order with the supplier. Colors may vary depending upon where the decomposed granite is quarried, so shop around.

The next step is filling the area between the header boards with the decomposed granite. This is where the most common mistake is made. The decomposed granite must be installed in thin layers, moistening and compacting each layer.

If applied all in one layer, the entire profile of the decomposed granite does not compact, and once the upper crust cracks, you have a sand box. Apply a layer of decomposed granite 1 1/2 inch thick and thoroughly soak the material with water. Allow the moist decomposed granite to sit for about eight hours and then compact it with a heavy roller or a vibrating plate compactor.

Apply another 1 1/2-inch-thick layer of decomposed granite and soak it thoroughly with water. Wait about eight hours and compact again. Since the material is compressed thinner than the one-and-one-half inch layers applied, a third layer usually needs to be applied to make the path flush with the top of the header board.

Now stand back and admire a job well done. If this all sounds a bit too labor-intensive, call a licensed landscape contractor who has experience installing decomposed granite paths.

QI have heard that coffee grounds are good for plants when applied to the soil surface. Is this true? ACoffee grounds can be used in the garden if applied properly. The most common use is adding the spent grounds to the compost pile and then applying the compost around plants in the garden, but they may also be applied directly to the plants. Coffee grounds have some nutrient value including about 2 percent nitrogen, 33 percent phosphoric acid and trace amounts of potash. They also contain other trace elements, carbohydrates, vitamins and caffeine.

As coffee grounds break down, they seem to encourage acetic acid-forming bacteria. Since they are acidic, they help to lower the pH of the soil. Coffee grounds can be used as a mulch for acid-loving plants such as rhododendrons, azaleas and camellias. They may also be mixed with lime and incorporated into the compost pile for use as a mulch on other garden plants.

Scott Loosley is the horticulturist at the Gamble Garden Center in Palo Alto. His column usually appears the third Friday of the month. Send questions to Loosley care of Palo Alto Weekly, P.O. Box 1610, Palo Alto, CA 94302.



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