Rain and Construction of Successful Granite Paths

Ah, the fun of rain in Texas, an all or nothing event. Hence the nickname for our zone “Flash Flood Alley.” What a treat for the Austin area to receive up to 12 inches of rain in some areas on Saturday night (October 12). The first significant rain in three years! (Take note those considering moving here from climates blessed with rain). Why that 12 inches cannot be spread out evenly over a month or two continues to baffle us gardeners. 

That is ok, we are inventive and can adapt our gardening design and style. Building a rain garden into your plan can help store water and moisture in your landscape for days if not weeks depending on the size. Rain barrels for collecting the water are something every home should be required to install. Rain water collection systems can be just that, a collection utilizing barrels of 50 to 75 gallons. Systems can grow up to harvesting plans that  include tanks of 300 gallons plus. 

No matter what your garden style, plans should be made for all the crazy weather central Texas has to offer. This means knowing where the sun beats down in the yard, knowing where the rain runs off your roof, and implementing materials in ways to keep your design stable. 

Decomposed granite, one of the materials of the garden commonly used here in central Texas, needs to be addressed after this heavy rainfall. Crushed or decomposed granite is a product used as mulch, walkways, and driveways. Since it is composed of small bits of crushed granite, it can be washed away easily when two inches of rain are falling per hour. To keep the granite on your property, I recommend designing wide edges and containment lines in long or sloped paths. 

I came upon this granite path in west Travis County on October 13. Notice the long run of just decomposed granite. This area probably received more than 12 inches of rain on the night of October 12. Also note there is weed barrier under the granite. 

It is a simple path, quick to lay down the barrier, put down a metal edge and just shovel some granite on top. Quick does not mean durable. This damaged path made me think of a landscape plan I worked on 5 years ago on the grounds of Laguna Gloria. After seeing this disaster, I knew the Laguna path would have held up. I want to share the construction process so you can build a successful path in your garden.

Below is the walkway made of granite and limestone at Laguna Gloria. The left image was taken days after construction of the walkway in 2009. The right image was taken October 14, 2013 two days after 12 inches of rain fell at this location in 6 hours. This path has a grade change of approximately 24 inches over 50 feet in length. It is 4 feet wide and and edged with limestone. Containment lines, or breaks, are perpendicular to the edge every six feet. These edges and containment lines keep the granite from migrating to the surrounding garden beds, turf, or from washing down down grade during heavy rains. This structure can be applied to driveways as well as paths. It can also be utilized with any other type of small surface material such as pea gravel or Tejas black-the grey stone.

The limestone bricks called chopped block, are generally available in two sizes based on width, and are locally quarried. Stones of different colors are available for the same purposes, prices will vary depending on where the stone comes from. Blocks of stone like this are purchased by weight. You can load your own truck or order a large load to be delivered by a dump truck. If you have a large multi-ton load delivered, designate a dumping area on your property that can handle the effects of all those rocks tumbling onto the ground! The crushed granite is purchased by volume, ordered in cubic yards. As with the stone, you can load your own or have bulk loads delivered. Each material is available in small quantities for small jobs or patch-up work. Bags of granite and individually priced blocks of stone can be purchased at most building supply stores and some nurseries. 

Constructing your path

Tools: wheel barrel, flat shovel, hose, square tamper or weighted roller, pick axe if your yard is rocky, hardware cloth, measuring tape. 

Before you start digging out turf or shoveling gravel, get your garden hose out and use it to outline your proposed path. Walk the outlined area a few times from each end to make sure you like the path. Once you have settled on a path, get ready to dig, and dig some more. If you are removing St Augustine turf grass, your chore will be bearable. The flat shovel pushed parallel under the grass surface will cut it off. This type of grass has shallow roots making it easy to remove. Bermuda has deep roots so more time is involved removing this bugger. Repeated applications of horticultural vinegar on the roots will help choke it out. After removing vegetation, remove about one more inch of soil. Sift the soil through hardware cloth to remove roots, runners, and nut sedge nuts. Recycle the soil into beds or compost. Grass roots and nut sedge nuts are difficult to compost, I recommend throwing them in the trash.

With the path free and clear, measure the length and width to calculate materials needed. My experience and suggestion for materials: one inch of builders sand or road base crushed limestone as the base of the path topped with two inches of decomposed granite. Other surface materials could be pea gravel or the grey Tejas Black angular rocks. Granite can be up to 3” deep. You never want more than 2” of pea or Tejas Black because your feet will sink into them making it hard to walk on. To calculate the amount of sand and gravel: Length of path in feet  multiplied by width of path in feet multiplied by depth of material in inches divided by 324 = cubic yards.

L ‘  x  W ‘  x D “  / 324  = cubic yards 

NOTE: I do not recommend  laying weed barrier down in the bottom of the path! You want your path materials to come in contact with the earth to keep them in place. Notice the photo above, the granite just washed right off the smooth weed barrier. Some builders recommend weed barrier to keep weeds from growing through your path. The only weeds that would grow through all this gravel would be Bermuda or nut sedge. These two are easily treated with horticultural vinegar as a weed killer. Any other weeds are going to fall on the paths as seeds and sprout from the surface. 

Edging can be limestone blocks or other stone of your choice, even concrete edging, plastic or metal edging. The brakes, however, should be a stone or concrete block at least four inches wide. A thin metal edge or plastic edge will not hold water streaming down your path pushing granite.

When ready to build the path consider constructing your path in sections, especially if it is long. Finishing sections will give you a sense of accomplishment each day. Trying to complete a whole landscape path all at once can be messy and may make the task feel overwhelming. 

Lay out approximately one inch of sand or road base for the base. The flat shovel is great to use for moving sand and granite, however a regular spade shovel will work fine. Tamp the sand down with a square tamping tool or roller (weighted rollers can be rented at some building supply stores or equipment rental shops). Place your stone edging along the edges of the path and the containment stones perpendicular to the path on the sand as well. Then fill the path with granite edge to edge. Tamp the granite with the tamper, spray it with a little water-a very short shower-then tamp again. It will settle some so spread a little more granite on top. Repeat the process for the next section. Sections should be no more than 6 feet long to keep granite contained. You may choose to make smaller sections which may be better for containing granite. 

Stand back and enjoy the clean line of your new path. Now it will be easier to get into the garden, move tools, and keep your path contained!