Initially a symbol of wealth and then prestige once push mowers arrived, lawn has lately become waste’s poster child. Shrinking water supplies call into question our 45 million acres of turf and our landscape irrigation that takes 30-60% of all residential water nationwide.
On a square footage basis, lawns generally use 4-6 times more water than plants in Western state guides. Governmental agencies, non-profits, and other reputable sources all agree on that, but no one explains why. This post lays out the reasons those little blades are such big water hogs:
1. Anatomical adaptations of alternatives. Drought-tolerant plants have adapted their biology to store water, limit loss, reflect light, and avoid sun. Although grass has not, upping summer mowing heights so it shades itself mimics that concept.
2. Roots vis-à-vis irrigation frequency. Shallow roots of grass need frequent rewatering, whereas deeper and wider root systems of shrubs, trees, and other plant types adeptly retain and capture water. Thus, lawn is irrigated 3-4 times/week, and plants 1-2 times or less/week.
3. Demands. Grass is organically thirstier: 1+” inch/week with gallons/minute spray heads, in vivid contrast to plants’ a few gallons or less/week with gallons/hour drippers. To illustrate, a lawn zone running 10 minutes with 8 2.1 gallon/minute pop ups takes 168 gallons. The same area with 40 plants, each with 2 gallon/hour dispersal, running 30 minutes takes 40 gallons. Factor in lawn’s more frequent irrigation, and the gap gets worse.
4. Coverage per square foot. Each blade gets saturated, so an entire area gets wet. By contrast, each plant gets a drip or two, surrounded by dryness up to the next plant’s drips a few feet or inches away.
5. Water losses. Sprays onto turf have wind, evaporation, and overspray losses. Drips at plants don’t. Industry resources cite spray efficiency as 50-70% to 80% best case, and drip as 90% or more. Put another way, spray wastes 20-50% and drip <10%.
Case studies encapsulate relative needs of lawns vs. climate-appropriate plants in like-for-like spaces. The City of Santa Monica’s rigorous nine-year garden\garden project compared two adjacent 1,900 square foot front yards. The one with traditional lawn and foundation shrubs took 5.5 times more water than its neighbor with native plants and no lawn.
Similarly, lawn consumed 5 times more than replacement plants, and carex 3 times more, in my 9,100 square foot conversions detailed at #1, #2, and #3. Low-flow MP Rotators cut water 30% on the little bit left, so now this 2% of irrigated area uses 12% of our reduced water tally.
The bad news takeaway for us turf lovers is that lawn expanses, especially in dry climates, are not viable. The good news is that amazing options exist, the subject of upcoming posts.