Gravel, Crushed Stone, Soil and Mulch Delivery in San Antonio, TX

Clay That Swells and Shrinks

At the ZIP's center point the USDA survey maps Houston Black clay, 1 to 3 percent slopes. The Houston Black series makes up 80 percent of that map unit. Its top mineral layer is clay, and the survey rates it moderately well drained.^[1]

The figure that stands out is shrink-swell. The survey rates linear extensibility in the top 100 cm at 12 percent, which it classes as very high. A clay like that grows noticeably when it soaks up water and pulls back, opening wide cracks, when it dries. Anything rigid set straight on it, from a paver patio to a concrete walk, rides up and down with it.^[1]

The fix is to separate the clay from the surface. A thick, packed layer of stone over fabric spreads the movement out, and keeping moisture in the clay as even as possible, by moving roof water away and not flooding one spot, cuts down how far it travels.^[1]

The dark color of this clay comes from organic matter, and the same ground turns fertile once roots can breathe in it.^[1]

Rain That Runs Off Instead of Soaking In

The survey places this soil in hydrologic group D, very slow infiltration and high runoff. Once the top of the clay is wet, most of the next rain flows across it instead of sinking in. On slopes of 1 to 3 percent that water picks up speed and carries loose material with it.^[1]

San Antonio Incarnate Word, TX, about 4 miles away, is the nearest NOAA normals station. It averages 34.0 inches of precipitation a year and a trace of snow, 0.1 inches. Much of that rain lands in heavy storms, so every gravel surface and bed needs a planned exit for water.^[2]

A swale lined with River Rock along the low side of a yard catches runoff and guides it to the street. A trench of Drain Rock around a perforated pipe works where water must move underground. On high-runoff clay, these paths matter more than how fast any single material drains.^[1]

Gutters and downspouts matter on group D soil. A splash pad of River Rock, or a buried line to a pocket of Drain Rock, moves roof water several steps away from a wall instead of dumping it right beside the slab.^[1]

A Short Freeze List and Long Growing Months

The station records 22 days a year when the low reaches 32 F or colder. Its median last spring freeze is February 25. The median first fall freeze there is November 28.^[2]

Cold is a minor factor for a base here, but those freezing nights do matter for plants. Tender vegetables and annuals go into beds after the late February date, and a layer of Brown Shredded Mulch or Wood Chips laid in late fall protects roots on the few cold nights that follow.^[2]

Summer heat is the bigger stress. Mulch over clay keeps the surface from baking hard and cracking, and it slows the drying that makes the clay shrink. Black Shredded Mulch and Red Mulch both do that job, and the color is a matter of taste.^[1]

Spring base work goes best after the clay has dried out from winter rain but before it bakes hard in summer. Clay packed at that middle moisture forms a firmer subgrade than clay packed soaked or cracked dry.^[1]

Houses and Yards in ZIP 78201

ZIP 78201 holds 18,416 housing units by the Census Bureau's count. Detached single-family houses make up 62 percent of them, a little above the 59 percent found across San Antonio and its 612,901 units. The median year built in the ZIP is 1952, decades before the city's median of 1985. Owners live in 49 percent of the occupied homes in the ZIP.^[3]

A ZIP where most homes are detached houses has plenty of driveways, side yards and garden beds. Those are the jobs bulk material serves best: a gravel parking pad beside a garage, a refreshed bed along the front walk, a path to a back gate, or a level patch for a shed.^[3]

Front walks and side paths are common small jobs. A path of Stone Dust Screenings over fabric and packed Road Base gives a firm walking line, while a border of River Rock along it catches runoff from the lawn.^[3]

A Driveway That Rides Over Clay

On a very high shrink-swell clay, a gravel drive has an advantage over concrete: it flexes instead of cracking. Build it by stripping the dark topsoil, packing the clay while it is moist rather than bone dry, and covering it with a heavy woven fabric.^[1]

A thick lower course of #4 Crushed Stone or 1-1/2" Crushed Gravel spreads the load and gives water an open layer. Road Base packed in thin lifts goes above it, and a surface of Driveway Gravel or 3/4" Crushed Stone finishes the drive. Crown the top so runoff from the group D clay leaves the sides quickly.^[1]

The Texas Department of Transportation names Flexible Base, Item 247, in its Standard Specifications for Construction and Maintenance of Highways, Streets, and Bridges. State road crews build to that item. A homeowner can ask for the material by its common name and pack it with care.^[4]

Edges are where gravel drives on clay fail first, because wet clay at the sides lets the stone spread. A firm edge of steel, stone or a buried timber holds the base in place, and a narrow strip of #57 Crushed Stone beside the drive gives runoff a place to drop before it reaches the lawn.^[1]

Beds Built Above Black Clay

Clay this heavy grows good plants once roots can reach air. Raised beds filled with Garden Soil, or native ground loosened with plenty of Compost, give roots that air. Topsoil spread over the clay builds up a planting layer for a lawn patch or a border.^[1]

Paths between beds do best with an angular stone that locks in place, such as #89 Crushed Stone or Stone Dust Screenings, laid over fabric so the clay does not swallow it. Pea Gravel is softer underfoot but drifts, and on clay it tends to sink and mix with mud after a few wet seasons.^[1]

Keep beds and paths sloped gently away from the house. With runoff rated high on this soil, water standing against a wall or slab soaks the clay unevenly, and even moisture is what keeps it from moving.^[1]

Trees planted in clay do best in a wide, shallow hole rather than a deep, narrow one. Backfill with the native clay loosened with Compost instead of pure Garden Soil, so water does not collect in a soft pocket around the roots, and finish with a ring of Wood Chips out to the edge of the branches.^[1]