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Learning about ground covers

If you are a gardener, enjoy landscaping or just like to visit the beautiful gardens, we have here in Encinitas at Swami’s or the San Diego Botanic Garden off Encinitas Boulevard, then you are probably quite familiar with the term “ground cover.”The term ground cover sounds just like what it is, a material or plant that is placed on the earth to cover up bare soil areas or steep slopes where erosion can be a problem. However, in the landscape world, ground cover can be inorganic or organic and often times results in many different outcomes depending on the application of the chosen material.

Sand, gravel, decomposed granite, or DG, beach cobble, wood chips, straw, bark, concrete, pavers, rock, flagstone and plants in my opinion are all ground covers. Many are used successfully with experience, but placed incorrectly, ground covers often become unattractive and problematic over time.

Concrete — although I am a definite plant lover — is one of my favorite ground covers. It has durability and only your imagination will limit you on how it can be finished or applied. It can transform a dirty backyard into a lovely patio setting, a raised walkway through the garden or provide the basis for a sports court, driveway or storage area.

However, the downsides to concrete are many. Heat collected from the sun can super heat the home during the summer and poor installation too close to the weep screed of the stucco without proper fall away from the home will invite mold, insect problems and dry rot.

Concrete installed over expansive soils will move and crack, dramatically ruining the aesthetic look and will lower the intrinsic value of your initial investment. It is important when using this type of ground cover to prep well before using it in any application.

Beach cobble, gravel or decorative rocks are also excellent ground covers. This material can be decorative in nature, colorful and be a great accent to an otherwise boring planter when used as a filler material. It is great in terms of low-water requirements and covers drip irrigation quite well.

Yet again, it can be a great source of aggravation when used or installed improperly. The interesting thing about most rock or stone is that it has a specific density much greater than the surrounding soils. Since gravity never sleeps, denser material like rock or gravel will eventually move downward in a substrate through moist soils disappearing until it is stopped by bedrock or another solid object.

If you have ever watched the reality show about gold miners in Alaska, you know that gold being 20 times heavier than water is always found in greater quantity in the lower strata of the soils which is usually just above bed rock. This is one of the reasons why it is important to place a filter fabric cloth under any decorative rock placement.
Not only will the fabric keep the rock from settling into the surrounding soils, but it will also (for the most part) prevent weeds and plant growth in this newly landscaped area.

Unfortunately, soils and leaf debris can over time wash into this rock ground cover and provide a soils base for more weeds. This can create another maintenance issue but one that is easily remedied with periodic cleaning.

Sand and decomposed granite can also be used in the landscape as a ground cover. Good compaction of DG is imperative to create pathways with it. I like to use a motorized vibraplate and a little water to achieve good compaction. I have tried mixing Portland cement with it (and several other products to make it bind better) but I have found that subsequent rains leach the lime out of the mix leaving an unattractive white residue on the surface only removed by repetitive scratching of the DG surface.

It’s better to mix it naturally with water and add a few small river cobbles near the surface for added aesthetic texture and body. Always mound your DG pathways for drainage. Green algae will grow in shade on wet DG.
The best ground cover of all I have found for erosion control between plants is mulch, tree chippings or organic material.