Why rock yards in Hesperia, Victorville and Apple Valley still grow weeds, when to put down pre-emergent here, and what to do about bindweed, Bermudagrass and nutsedge.
Get a Free Rockscape EstimateTo keep weeds out of rock and gravel in the High Desert, apply a pre-emergent twice a year (late February to mid-March for summer weeds and late August through September for winter weeds, by our estimate from NOAA data), water each application in with about half an inch of water, and pull anything that gets through before it seeds. Landscape fabric under the rock helps, but it will not stop yellow nutsedge, Bermudagrass that finds a gap, or seeds that blow in and root in dust on top.
UC IPM does not sugarcoat it. Rock mulch is “difficult to keep weed-free,” and removing weeds from rock by hand weeding or hoeing is very difficult (UC IPM Pest Notes 7441).
It is part of our High Desert weeds guide.
Weeds get into a rock bed three ways:
Pre-emergent handles most of the first two. Drip and good drainage handle the third.
Pre-emergents stop seeds from sprouting. They do nothing to weeds already up. UC IPM gives the trigger as soil temperature: apply before the soil at 1 inch deep goes above 55 to 60°F (UC IPM, spotted spurge). For crabgrass, UC says germination starts at 55°F for several consecutive days, and its regional windows for southern inland valleys run mid-February to early April (UC IPM, crabgrass). UC gives no High Desert window.
We used Victorville’s 1991-2020 NOAA normals. Mean air temperature is the average of the normal daily high and low (NOAA):
| Month | Avg high | Avg low | Mean air temp | Rain |
|---|---|---|---|---|
| February | 61.0°F | 35.9°F | 48.4°F | 1.27 in |
| March | 66.8°F | 40.1°F | 53.4°F | 0.78 in |
| April | 73.1°F | 44.2°F | 58.6°F | 0.33 in |
The mean air temperature crosses into UC’s 55 to 60°F range between March and April. Soil temperature does not track air temperature exactly, so we put the application ahead of that crossing: late February to mid-March on the valley floor for summer weeds like spurge, goatheads and tumbleweed. Colder low spots and higher lots in Phelan and Oak Hills run later.
For winter weeds (Sahara mustard, London rocket, filaree, red brome), UC IPM says to apply in late summer to early fall (UC IPM). Here that means late August through September, before the first real fall rain. Victorville’s normals are 0.31 inches in October, 0.35 in November and 0.94 in December (NOAA).
Not by itself. Pre-emergents have to be moved into the soil. UC IPM calls for about 1/2 inch of water soon after the application (UC IPM), and says that if the product is not moved in by irrigation or rain, more than one application may be needed (UC IPM).
At Victorville, every month from April through September averages less than 0.35 inches of rain (NOAA). Do not wait for a storm. Drip emitters only wet small circles, so water the whole bed by hand after you apply.
We do not recommend brands. These are the active ingredients UC IPM lists for the main summer weeds found in rock beds:
| Weed | Pre-emergent actives UC IPM lists | Source |
|---|---|---|
| Spotted spurge | pendimethalin, trifluralin, dithiopyr, oryzalin | UC IPM |
| Puncturevine | oryzalin, benefin, trifluralin (partial control) | UC IPM |
| Russian thistle | isoxaben, oryzalin, pendimethalin, trifluralin | UC IPM |
Always follow the product label. Many products are not labeled for every plant or site, and some can damage the shrubs and trees in the same bed.
Usually yes, for a bed that will stay put. UC IPM’s pros and cons:
| Pros | Cons |
|---|---|
| Keeps rock pieces from sinking into the soil (UC IPM). | Plant roots grow into the fabric, and pulling it out damages them. UC flags this as a concern once fabric has been down longer than 5 years (UC IPM). |
| Keeps soil and rock from mixing, which favors weed growth (UC IPM). | Yellow nutsedge can grow through most geotextiles (UC IPM). |
| Cost-effective if the planting will stay in place 4 or more years (UC IPM). | Bermudagrass grows through any holes or gaps (UC IPM). |
| Covered with rock, it will likely keep field bindweed from coming up (UC IPM). | It does nothing about seed that lands on top of the rock and roots in wind-blown dust. |
UC IPM does not give a rock depth for weed control. Its mulch depths are for organic mulch: about 2 inches for fine material and up to 4 inches for coarse, with deeper than 4 inches risking harm to roots (UC IPM).
The common trade practice for decorative rock is 2 to 3 inches over fabric. That is an industry habit, not a tested number. One related UC data point: spotted spurge seed buried deeper than 1/2 inch does not germinate well (UC IPM).
For desert native plantings, the Mojave Desert Land Trust recommends rock or gravel mulch over bark (MDLT). That fits how most High Desert rockscapes are built.
Field bindweed has arrowhead-shaped leaves and white to pink flowers (UC IPM). It is hard to kill because the vertical roots can go 20 feet or more and the seed can stay viable for up to 60 years.
UC’s options: landscape fabric covered with rock will likely keep it from emerging, but it takes 3 to 5 years of blocking light to wear the roots down. For plants already up, UC lists glyphosate as a 2% solution applied when the plant is actively growing, repeated through summer (UC IPM). Follow the product label.
Bermudagrass is a common invader when an old lawn gets converted to rock. It spreads by rhizomes 1 to 6 inches deep and by runners on top, and broken pieces re-root. Mulch alone fails because it can push up through, and fabric only works if there are no holes or gaps (UC IPM).
Nutsedge looks like grass but has triangular, solid stems where grasses have round hollow ones. Yellow nutsedge makes round smooth tubers underground (UC IPM).
UC IPM says its presence often means poor drainage, irrigation that runs too often, or leaky sprinklers. Remove plants before they have 5 to 6 leaves, which in summer is about every 2 to 3 weeks, and dig 8 to 14 inches to get the tubers. Plastic sheeting fails against it. UC’s nutsedge note says polypropylene fabric suppresses it (UC IPM), while its landscape note warns it can grow through most geotextiles (UC IPM), so do not count on fabric alone.
The real fix is the water. Switching a rock bed from spray heads to drip and fixing leaks is irrigation work. Standing water after storms is a drainage job.
Twice a year. Our estimate from Victorville NOAA temperature data is late February to mid-March for summer weeds, before the soil at 1 inch passes the 55 to 60 degree trigger UC IPM gives, and late August through September for winter weeds, before fall rain. Check with a soil thermometer, since UC does not publish a High Desert date.
Only if you water it in. UC IPM calls for about half an inch of water soon after applying, and says more than one application may be needed if it is not moved into the soil. Victorville averages under 0.35 inches of rain every month from April through September, so plan to water it yourself.
For a bed that will stay in place four years or more, UC IPM says fabric is cost-effective. It keeps rock from sinking and soil from mixing into the rock. The downsides are that roots grow into it, yellow nutsedge can grow through most fabrics, and Bermudagrass comes through any gap.
Fabric only blocks weeds from below. Wind drops dust and seed on top of the rock, and over time weeds root in that layer. They are shallow and easy to pull if you get them before they seed, and a pre-emergent watered into the rock helps.
UC IPM lists the grass-selective herbicides clethodim, fluazifop-p-butyl and sethoxydim for Bermudagrass, applied while it is green and growing, following the product label. Before rock goes down, UC lists solarization during high-sun months. Fabric only helps if it has no holes or gaps.
We checked every number on this page against the public sources below. If a rule or date changes, the agency page is the final word.
When a rock yard keeps growing weeds, the cause is usually underneath: no fabric, thin rock, soil mixed into the stone, old Bermudagrass, or spray heads watering everything. Monarch rebuilds rockscapes and converts beds to drip. Get a free estimate and we will tell you whether it needs a rebuild or just a better routine.
Get a Free Rockscape EstimateOr call (760) 792-7627
