5 Rules For Getting The Most Benefit From Rainfall In Your Garden

Rain is the cheapest water a garden will ever get, and much of it is wasted. Some evaporates before it soaks in, some runs off into the street, and some falls on soil that is already full. Whether you tend a vegetable patch, a few shrub beds or an allotment plot, the same rules decide how much of a storm the plants actually use.

1. Measure what fell where you are

Rainfall varies over short distances, especially in summer showers, so the total reported at the nearest airport can be far from what reached your beds. A simple rain gauge mounted in the open, away from trees and roof edges, settles the question. Note the time as well as the amount. The National Weather Service describes rain falling at up to a tenth of an inch per hour as light, from a tenth to three tenths as moderate, and more than three tenths as heavy.

2. Count only the rain that is stored

The useful share of a storm is the water that ends up in the root zone, often called effective rainfall. A light shower on hot, dry soil may wet only the top half inch, much of which evaporates within a day, and some never gets past leaves and mulch. A cloudburst can deliver an inch in an hour, faster than many soils can absorb, and the surplus runs off. Steady, moderate rain over several hours is the kind that refills the soil.

3. Know how fast your soil drinks

Sandy soils take in water quickly, often more than an inch an hour, but hold little of it. Clay soils hold a great deal, yet may absorb only a fraction of an inch an hour, so heavy rain ponds and runs off. Loams sit in between. Compaction, crusting and slopes all slow infiltration further. Adding organic matter and keeping the surface mulched helps both kinds of soil: it opens clay so water enters faster and gives sand more capacity to hold it.

4. Watch the soil before and after rain

If the soil is already moist, rain mostly drains past the roots or runs off. Avoid watering the day before rain is likely, and after a soaking rain, check the soil a few inches down before the next scheduled watering instead of returning to the routine. A timer fitted with a rain or soil moisture sensor makes this automatic.

5. Catch it and slow it down

Roofs shed a lot of water. Nebraska Extension uses the rule that about 0.6 gallons falls on each square foot of roof in a one-inch rain, so a 1,200-square-foot roof yields roughly 750 gallons. A rain barrel stores a small share of that for dry spells, and a downspout aimed at a planted bed or a shallow rain garden sends more of it into the ground instead of the storm drain.

Keep barrels covered with a lid or fine screen, since mosquitoes need only a week or so of standing water to breed, and use dark or opaque containers to limit algae. The same Nebraska guide does not recommend roof water for fruit and vegetable gardens, because runoff can carry bacteria from bird droppings and chemicals from roofing materials. Use it on ornamental beds, trees and lawns.