Thursday, November 19, 2009


Today we have another splendid article by P. Garden supporter and Potrero Hill resident Josh. Enjoy!

Mulch is such an evocative word. It always makes me think of something vaguely mysterious, with an earthy smell and unclear origins. In reality, mulches are one of the gardener’s best friends. There are many different materials that can be used as mulch, but they all have many of the same benefits for the garden. Mulches shade the soil, keeping plant roots cool in the hot sun, and warmer at night when the air temperature drops. Mulches also help the soil retain water, so that the soil moisture is more even between waterings, and can reduce erosion from water runoff. Mulches can also reduce weed growth in the garden. Many types of mulch decompose over time, adding nutrients to the soil. Besides these practical reasons for using them, many mulches just make a garden look nicer.

There are organic and inorganic mulches. The inorganic mulches include plastic sheeting, gravel, tumbled glass, and in some gardens, bowling balls and broken dinner plates. Obviously, these mulches are not going to break down and add nutrients to the soil, but they will perform all the other roles of mulch that are listed above. Some plants, such as succulents and cacti, don’t like lots of organic stuff in their soil or at their feet. Inorganic mulches, such as pebbles, gravel and rocks, are ideal for these plants. I’ve seen tumbled glass  used as a striking mulch in several gardens. There are few limits in terms of materials that can be used as inorganic mulch, so let your imagination run wild!

The organic mulches include straw, garden compost, leaves, pine needles, cardboard, newspaper, wood chips, bark chips, cocoa hulls, sawdust and lots of other materials. All of these are derived from plants, and will break down over time and add nutrients to the soil. Generally speaking, no matter what kind of organic mulch you use, plan on using at least a 3-inch thick layer of mulch between plants. Keep the mulch away from the bases of plants in order to allow water to enter the soil and to keep the bases of the plants from rotting.

Depending on the material you want to use, there are many sources for mulch. The deep, luxurious mulch in the Pennsylvania Garden was donated by the Bay View Green Waste Management Company. You can contact them if you are interested in getting some mulch for your garden - they make their mulch from the contents of the city’s green bins.

If you are curious about this mulch, check it out the next time you are in the garden. Carefully stick your fingers in one of the planting beds and lift up a bit of the mulch. You will probably find that it is dry on top and moist further down. Most of the beds in the garden are thickly mulched (4 to 6 inches) to help compensate for the lousy soil, so you probably won’t hit dirt if you stick your finger in it. An added benefit of this thick mulch is that the weeds that do manage to grow are usually really easy to pull out! The succulent beds have much less mulch, and we are hoping to get some gravel to use in these beds. If you have any unwanted gravel, let Annie know!

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