Knowledgebase
Inorganic Mulch - Pea Gravel vs. Squeeze #874893
Asked June 26, 2024, 10:30 PM EDT
Hello, I am replacing most of the sod in my front yard with native, low water plants. I am planning on using inorganic mulch because I've read a lot about how Colorado plants do well in it. Does it matter whether I use pea gravel (which is consistently 3/8" in size) or squeege (which is more variable in size with a max of 1/4"). Why or why not? Thanks :)
Weld County Colorado
Expert Response
Mr. Bennett,
You ask about inorganic mulch--pea gravel v. squeegee.
Here is (inconclusive) research-based information from Colorado State University Extension:
Many resources recommend adding rock, gravel, squeegee, or sand to garden beds where native or drought tolerant plants will be grown, in order to improve drainage. Published scientific papers provide mixed conclusions about this practice; in many cases it is clear that adding gravel or squeegee as a soil amendment makes drainage worse. [Emphasis is mine. S.] Deep infiltration (i.e. “drainage”) is unequivocally promoted by mulching with gravel, however. The incorporation of soil amendments, inorganic or organic, will be site-specific, and should be considered in context and not as a blanket prescription.” (Source document: https://extension.colostate.edu/topic-areas/yard-garden/choosing-a-soil-amendment/)
An earlier bulletin states: “Pea gravel increases water filtration and can improve growth of perennials especially in water-conserving gardens. Larger sizes (greater than 0.5 inches) do not prevent weeds well and are not as beneficial for water savings as smaller stones.” (From table 2 in https://extension.colostate.edu/topic-areas/yard-garden/mulches-for-home-grounds-7-214/ )
More information about xeriscape mulches and amendments can be found here: https://planttalk.colostate.edu/topics/water-wise-xeriscape/1905-xeriscape-mulches/ and here https://planttalk.colostate.edu/topics/water-wise-xeriscape/1908-xeriscape-soil-amendments/
This CSU bulletin gives general information about planning a water-conserving garden: https://extension.colostate.edu/topic-areas/yard-garden/xeriscaping-creative-landscaping-7-228/l. You did not ask, but plastic sheeting and landscape fabric are no longer recommended. Our friends down in New Mexico have information too: https://pubs.nmsu.edu/_h/H707/index.html
Just to be sure I am giving you the information you want—are you interested in CREVICE GARDENING, which is a whole ‘nother topic, a subset of water-conserving gardening? See this brief CSU bulletin: https://arapahoe.extension.colostate.edu/2024/05/02/gardening-in-the-cracks/
Water conserving gardens may be seen at the Gardens at Spring Creek (Fort Collins, CO), Cheyenne Botanic Garden (Cheyenne, WY) and Treasure Island Demonstration Garden (Windsor, CO).
Hope this helps. If you have additional questions, please do not hesitate to contact CSU Extension again.
Sue, Weld County Colorado Master Gardener
