Inorganic Mulches

Inorganic mulch is anything that is not an organic material, in other words, anything that is not made from plants or plant byproducts. Inorganic mulch has the benefit of being more permanent. But that is also its biggest disadvantage because, unlike organic materials, it does not break down and enrich the soil.

Traditionally inorganic mulch has usually meant rock or gravel. There are a wide variety of rocks available to give a range of different colors and textures. Rock is as close to permanent as you can get. It doesn't float away easily and most of all, if done right, it is beautiful. Rock will usually cost much more initially, but won't have to be replaced regularly like wood mulches.

The most popular rocks are crushed marble and egg rock. Crushed marble comes in white, brown, green, grey and pink. Egg rock is smooth, rounded river rocks and comes in several shades. There is "white" which is a mixture of white and light browns, "brown" which is mostly medium browns and another which I know as "river jacks". It is a mixture of black, grey, brown and reds. River rocks usually are graded by size and offered in 3 or four different sizes. The smallest river rocks, usually 1/4 to 1/2 inch are called "chattahoochee".

Other available types of rock are crushed granite that is usually black and white speckled, lava rock, which is available in red or black and another volcanic rock that is one of my personal favorites. Different companies sell it under different names, but I know it as Timber-lite. It is rough textured, medium sized pieces that are mottled brown, black and tan. There is also a rock sold as "Cedar Bark Rocks" that is a brown rock that looks very much like chunks of cedar bark. If you like the looks of bark but don't like the fact that it is prone to floating away, this might be a good choice. There are also some fancier, more expensive rocks available if you are looking for something really special. Among others there are "Mexican Beach Pebbles" that are round, flat smooth rocks that come in a number of sizes and colors. In the picture above are Columbian River Rocks in red and gold.

If you are considering using rock in your landscape here are a few tips:

• Light colors like white marble chips look spectacular when you first put them down, but they quickly get dirty looking from algae and debris like grass clippings and leaves. A darker color will camouflage a lot of that and look better longer. That is one reason I like the Timber-lite.
  

• Lava rock usually doesn't do well in shady, wet areas. Moss, algae and pilea tend to get rooted in the large pores and is very hard to control.

• Rock is usually available in bulk, by the cubic yard or in 1/2 cubic foot bags. By the yard is usually about 25-50% cheaper, but it is a lot more work. Unless you are doing a large area that will require several yards, I would go with the bags. If you have it delivered in bulk, you have to pile it somewhere and then shovel it into a wheel barrel to distribute it where you want it. Then you have to clean up where the pile was. With the bags, you just carry them to where you want them, open them and dump them. Usually you want the rock about an inch and a half to two inches deep. That means that a bag will cover 3-4 square feet. Usually large rocks, like extra-large egg rocks will need to be a little deeper and small rocks like chattahochee, not quite as deep. The reason being that big rocks mean bigger gaps between them. If you like the look of the extra large egg rocks, I would suggest buying about half extra large and half medium. Spread the medium first and then the large on top. You get better coverage that way, saving some money, but still get the look of the larger rocks. If you buy by the yard, a yard will cover about 150 square feet.
  

• Always use a good weed mat under your rock. In our sandy Florida soil rocks have a way of slowly sinking into the sand and disappearing! A weed mat will keep them on top.
  

• Always use some type of edging between rock areas and lawn. I usually use a commercial grade plastic edging but you can use stone, brick or any other you like. If you don't use some type of edging. the stones will invariably get spread into the lawn and the lawn will grow into the rocks. If you try to edge with a power edger, you will be hitting rocks which is hard on the machine and dangerous for you.

Besides rock, there is also now rubber mulch! It is made from recycled tires and dyed in a variety of colors, including blue and green! It is very permanent. It is available in different textures and grades, some with the steel belts completely removed, some not. If it is going to be in a play area or someplace you might be walking barefoot, it is very important that you get it with all the steel removed. It is fairly expensive, usually $10-20 for a 1 cubic foot bag, but the price seems to be coming down. It can give a very nice effect and is a good use for old tires. It washes away easier than rocks but not as easily as wood. Again, I always use weed mat and edging with rubber mulch.