Do you have a use for an inorganic mulch?

By Melanie Mathieson
Gardening Guru

Inorganic mulch products are used in a garden setting differently than many of the organic mulch products listed in a previous column. Not all gardeners have a use for the inorganic mulches available on the market today so take the time to read the summary of the inorganic mulch products listed and see if you even have a need for any products like this.
Stone mulches are quite versatile in that you can use them in the garden or in areas of your yard that have no plants such as pathways. Stone mulch can be added to your gardens once planting is complete to add interest and texture to your landscape design. You can purchase stone in bulk, directly from a gravel supplier, or your local nursery/landscaper or bagged from the large retailers in the area. Prices will vary depending on the type of stone you want, whether it is native to the area, and whether you buy bagged or in bulk. Stone mulch can be used to create pathways or borders along gardens, just make sure that you install a barrier to keep the stone in place and prevent the lawn mower from throwing stones when you mow the lawn. Stone mulches make a great groundcover in rock gardens, or to showcase special theme plantings and is excellent for camouflaging problem areas by installing dry creek beds. Stone can also camouflage areas that accumulate water and have poor drainage in the yard. Alternatively they is can also be laid out in areas that are too dry or compacted to support plant life. Stone installations can also be a great tool for placing in areas that are difficult to mow but still seem to grow odd weeds or patches of grass, just make sure you use a landscape fabric first. You can also use different sizes, textures and colours to make different patterns in your designs as well.
Stone Mulch
•Appearance: Good, if used around trees, in rock gardens or pathways; sometimes not aesthetically appropriate for vegetable or flower gardens.
•Insulating value in summer: Fair. Stone tends to heat up, but it also retains much of that heat within itself.
•Insulating value in winter: Fair. Natural stone retains the heat of the day at night but also the cold of the night during the daytime.
•Need to remove in spring: No, considered a “permanent” mulch
•Nourishment and aeration afforded to underlying soil by decomposition: None
•Lets water and oxygen move freely into soil: Yes but varies depending on size and thickness of stones used.
•Ease of application and maintenance: Good, long lasting as it doesn’t biodegrade.
•Is a “permanent” installation so be sure this is what you want.
•For best results you should use a landscape fabric (adds an additional cost) as an underlay before adding the stones on top.
•Not recommended for an area that you are still adding plants or landscaping. Install once plantings are complete.
Gardeners have used plastic sheeting in their gardens for many decades. There are a few different types of plastic that can be used in the garden so make sure if you decide to use plastic in your garden choose the right one.
Black plastic - One layer of black plastic provides excellent weed control. It is relatively slow to decompose, but will be somewhat broken down by sunlight and must be replaced every two years at least. Black plastic mulch will increase the soil temperature by about 8°F in the spring. It may cause soil temperatures to rise too much in mid-summer, damaging the roots of plants unless a thick covering of organic mulch is applied over the plastic, to prevent direct absorption of sunlight. Make sure to check periodically to see that soil remains moist beneath the plastic; cut holes in it if water doesn't seem to be getting through. Black plastic is easy to obtain, but is fairly expensive. In some garden supply centres you can find a black plastic that is porous to allow penetration of water and exchange of gases between the soil and air.
Clear plastic - One layer of clear plastic will provide little weed control; in fact, it makes an excellent environment for growing weeds, because it acts like a greenhouse. This material is most often used to warm the soil temperature early in the spring to prepare an area for planting. It will raise the soil temperature by 10°F or more. Clear plastic is readily available and somewhat less expensive than black plastic but should be removed from the garden area once you have achieved a warmer soil environment.
Red plastic - Developed and patented by scientists. Red plastic mulch boosts tomato yields in research plots up to 20 percent, while conserving water and controlling weeds. Red plastic mulch reflects onto the plants higher amounts of certain growth-enhancing light waves from sunlight. In 3 years of field tests, red mulch boosted tomato size and weight by increasing the plant's growth above the ground--especially in the fruit. The scientists also claim that the red plastic mulch can improve strawberry flavour by changing the fruit's chemistry. The scientists say their research has focused on two color components of reflected light to enhance plant growth--the percentage of blue and the ratio of far-red to red. The red plastic mulch has a low blue component and a high far-red to red ratio thus creating an enhanced growing environment. Numerous garden supply catalogues carry this product. You may want to give this a try if you want to grow prized tomatoes.
Plastic Sheeting
•Appearance: Poor, unless you are striving for that "hi-tech" look.
•Insulating value in summer: Plastic keeps the moisture already in the soil from escaping, but also heats up the ground considerably.
•Insulating value in winter: Fair
•Need to remove in spring: Yes if you need to plant there or you can cut holes in it.
•Nourishment and aeration afforded to underlying soil by decomposition: None
•Lets water and oxygen move freely into soil: No
•Ease of application and maintenance: Excellent
•Is recommended if you want to use it for weed suppression in a part of the garden where nothing is planted, for warming up the soil rapidly in the spring or are trying some vegetable garden growth experiments. Using some of the coloured or engineered plastics specifically for growing certain vegetables are well worth a try.
•Not recommended for use in perennial beds or as an underlay for stones or bark in an ornamental garden as the plastic will break down and start to break apart under the stones and then it is very messy and hard to remove or replace.
•Keep in mind that plastic can create a great deal of excess garbage if it gets damaged or you are unable to use it again.
Other inorganic mulches:
Ground or shredded tires - ideal for use in playgrounds, due to cushioning capabilities but not conducive for landscape use.
Recycled tumbled glass – can look like pea gravel but limited in its colour. Only available near glass recycling facilities.
Crushed brick – can look like rocks from far away. A good way to recycle a product that would otherwise end up in a landfill. Can sometimes be found bagged in stores but cannot be bought in bulk in our region.
Landscape Fabric – sometimes referred to as an organic mulch but must be used in conjunction with either an organic or inorganic mulch product.
I hope this column has helped you to understand how you can use inorganic mulch products in your yard or landscape projects.