Garden Watering Time Liters

Garden watering: the 1-inch rule and irrigation time

Most gardening guides settle on the same figure: 1 inch (2.5 cm) of water per week across the planted bed. To turn that into liters, multiply the area in m² by 25. Take a 20 m² garden as an example. That works out to 20 x 25 = 500 L/week. Divide by your system's flow rate and you have the run time. A hose pushing 8 L/min would need 500 / 8, or roughly 62 min/week, which is best broken into 2–3 deep sessions. How you deliver the water changes the math. Drip irrigation gets about 90% of the water down to the roots, whereas overhead sprinklers bleed off 30% to evaporation and wind and end up around 70% efficient. Water in the early morning whenever you can. The leaves dry off before nightfall, which keeps fungus down, and the soil loses far less to evaporation than it would at midday.

Applications

Programming automated irrigation on Rachio, Rain Bird or B-hyve controllers, sizing a drip system, planning a landscape, urban farming, balcony gardens, working out how big a rainwater cistern should be. It also helps when you're budgeting the water bill or trying to stay inside municipal limits during a drought.

FAQ

Daily or weekly? Take the weekly total and spread it over 2–3 deep waterings. That beats a quick splash every day, because deeper roots hold up better in a dry spell.

Does rain count? It does. Subtract whatever fell that week (mm = L/m²). A 15 mm rain over 20 m² hands you 300 L for free.

Drip vs sprinkler? Drip wins on efficiency (90% vs 70%), uses less water and keeps leaf disease down. A sprinkler covers a big lawn faster, though.

Hot summer? Bump it up 25–50% through a heat wave, and cut it in half when the week turns cool or overcast.