Mountain Gardener: Soggy spots can prove a valuable resource

We had enough rain this month to place those soggy areas of the garden you’ve been vowing for years to do something about at the top of the to-do list.
Whether they’re caused by excess rain on your property, from a neighbor or from poor soil drainage, wet spots can be a challenge or an opportunity when designing the garden.
One way to handle runoff is to intercept the water and drain it away with an open ditch, French drain or underground pipe. Better still — develop an on-site collection system.
Dry river beds can be designed to help with rainwater harvesting. Aboveground water tanks and submerged collection tanks are becoming common tools for saving excess water that flows off the impervious surfaces of your roof, patio, walkways and driveway. Another method of retaining water on your own property is to channel it into a dry-well, a hole filled with drain rock. From there, the water can disperse slowly into the surrounding soil.
Soggy spots can also be caused by compacted or clay soils. Sometimes a single plot of land can have a complex pattern of soils that varies sharply from one area to another. Or soil can become compacted by heavy equipment and needs to be broken up with a backhoe or an excavator, or by hand with a pick.
In some cases, natural topsoil may have been scraped away, as is sometimes the case after septic work, leaving the hardpan underneath exposed. This can be broken up and lots of compost dug in to keep it loose. New topsoil might be needed to increase fertility and drainage.
If you still have a naturally wet area, you may choose to live with it and select plants that thrive in damp conditions. A rain garden, one type of on-site collection system, is a depression made in the soil and planted with wet-tolerant plants. It can be as small as 100 square feet.
To create one, dig a shallow bowl, or build a berm along the edge to hold in the water. Runoff water diverted to a rain garden is slowed so it can seep into the soil. Such a garden also filters out pollutants than run off from buildings and driveways.
Choose plants that will thrive in wet winter and dry summer conditions. Native plants that will do well include trees like alder, sycamore and California fan palm. Native shrubs that tolerate these conditions are spicebush, pacific wax myrtle, western mock orange and sambucus.
Some native perennials to try are western columbine, wild ginger, Carex pansa, deergrass, red fescue and wild grape.
Ornamentals that don’t mind having their feet wet include bee balm, New England aster, ligularia, Lobelia cardinalis, hosta, calla lily, lysimachia and Japanese iris, and some grasses and grass-like plants that work in this situation are acorus, chondropetalum, fiber-optic grass, cyperus and equisetum.
Think of all the coming winter rain and moisture as an opportunity in your garden.
• Jan Nelson, a California certified nursery professional at Plant Works in Ben Lomond, will answer questions about gardening in the Santa Cruz Mountains. E-mail her at [email protected].