The National Weather Service has the storm flag flying for Northern and Central California next week. Two storms are headed our way, according to the 16 km infrared Western U.S. satellite map : a small, cold one late this weekend; then, further out in the western Pacific, is a huge band of moisture that may or may not dump on us (depends on the northerly movement of the high pressure area over us now).
When storms come blowing and pouring through our area each winter, think about this: Where is all that water going when it lands in your backyard? If that precipitation is going nowhere, here are some tips to protect your prized outdoor plants located in low lying areas from getting waterlogged roots:
• Enjoy the rain...from indoors. Working in wet soil causes soil compaction.
• If the source of the standing water is the runoff from the roof gutters that are dumping next to the house's foundation, buy some flexible plastic extension pipes and attach these to the end of the gutters, directing the runoff to another area less prone to flooding, at least six feet away from the house.
• Amending your garden area with porous material also will aid drainage. When the soil is dry enough to work, add organic soil amendments, such as compost. Till these materials in as deep as possible.
• Dig a sump. A hole that is dug in the lowest portion of your yard, a hole that penetrates through all the layers of hardpan (usually 2-4 feet below the surface), can help drain away stormwater. Line the hole with a non-porous material (hard plastic sheeting, for example) to keep the surrounding dirt from falling back into the hole. Fill the hole with small rocks, about one inch in diameter.
• If it's the lawn area that's flooding, dig a trench and lay a drain line in the lowest area of the lawn. Don't do any digging immediately after a heavy rain, though; wait until the soil dries enough to avoid unnecessary soil compaction. Be sure to slope the perforated drain pipe, allowing at least a one foot drop for each 100 feet of length (one quarter-inch per foot). Dig backwards from where the water will exit the pipe, trenching back towards the source of flooding to help determine how deep to lay the drain pipe. Line the trench with a few inches of gravel, both above and below the pipe. For a lawn area, try to lay the pipe at least two feet below the surface.
• If it's the garden bed that's flooding, consider building raised beds this fall, lining the bed with 2X8, 2X10 or 2X12 redwood planks. Capping off the top of these boards with 2X6 redwood will give you a comfortable place to sit while harvesting vegetables and pulling weeds.
• If you haven't planted in a flooded area yet, consider creating mounds first, planting trees and shrubs on the top of the mounds.
• If you're still stuck with pools of standing water after heavy rains despite your best efforts, consider planting trees and shrubs that can take "wet feet". Water-tolerant trees for our area include birch, sweet gum, magnolia, tupelo and coast redwoods. Shrubs for wet areas include thuja and red twig dogwood.
Landscape designer Michael Glassman offers these tips for improving drainage in your yard (downloadable audio segment runs 13 minutes).