This is the third article in a three-part series on efficient watering.

Instructions for waterwise gardening often suggest deep watering once a week and applying no more than one inch of water, including rainfall. For Salvia, this amounts to what we would call regular or average watering for in-ground plants. Potted plants may not require more water, but they do need more frequent watering.

Figuring out the volume of water that equals an inch for a particular garden area requires some basic math, which begins with the estimate of 1 inch of water equaling about .62 gallons per square foot.

Let's imagine you are calculating how much water to apply once a week to a perennial screen -- 18 feet long and 6 feet deep -- of Mexican Mountain Scarlet Sage (Salvia gesneriiflora 'Mountain Form') and Jean's Purple Sage (Salvia x 'Jean's Purple Passion'). Both species need regular watering and grow about 6 feet tall and wide. This would equal a bed of 108 square feet.

To find out how much water this garden bed will need, multiply 108 times .62 for an answer of about 67 gallons of water once a week. Remember to water early in the day to avoid evaporative loss.

If you don't yet have a digital garden hose meter attached to your sprinkler or drip system, one old-fashioned way of checking volume over a short amount of time involves empty tuna fish cans. Eight is a good number of cans for our hypothetical screen.

From the base of each can, measure up 1/2 inch and 1 inch, drawing lines with an indelible marker. Place the cans throughout the planted area. Water for 30 minutes; then check how full the cans are. Note variations from one part of the bed to another in case adjustments may be necessary in the positioning of your sprinkler head, hose or drip lines.

Remember that perennials, shrubs and trees require slower watering than your lawn. If the tuna cans are spilling over after 30 minutes, you are watering too quickly and need to slow down the flow.

If the cans reach the half-inch mark in 30 minutes, then you increase the watering time to 1 hour to deliver an inch of water.

Back to digital hose meters: These days, public libraries check out far more than books. So although it is clever, it isn't too surprising that the Austin Public Library in Texas checks out hose meters to aid the city in its conservation efforts.

You can't save water until you know how much you use. If you have any questions about the water consumption of the plants we grow at Flowers by the Sea, please call or write.