We are challenged by water on the central coast of Oregon.
In the summer, at the height of our growing season, it can be downright scarce. At that time of year, it's plain that the lack of planning for adequate water-- given our wind and sandy soil-- is to blame for many gardening failures.
But in January... oh yes and November, December, February, March etc... it's the opposite. We receive some of the highest rainfall counts in Oregon, 70-90 inches. Cascade Head, only 10 miles north of Lincoln City where I live, receives around 100 inches per year. By comparison, Portland receives merely 37-40 inches. Gives you some idea of what is considered "normal rainfall" on the central coast.
So what happens to all that water? Certainly the vast majority ends up in our rivers, streams and eventually the ocean. But it has to get there first... which gets me to the point of this post's title. Many homeowners here just don't plan for where the deluge is going to go, and what damage or benefit it may leave in its path.
One of the most obvious and lasting effects is on our soil. High rainfall totals equal acidic soils. Did you ever wonder why our soils west of the Cascades are "acid" and those east of the mountains are "alkaline" or less acidic? The falling rain leaches minerals like calcium and magnesium. In order to make our soils more palatable to the widest array of plants therefore may require annual applications of lime to boost the pH level. This is generally recommended for vegetables and lawns, and many other herbaceous plants.
The soil is likewise compacted by the constant falling rain, if it's exposed throughout winter. Protecting unplanted areas with mulches (bark, compost, straw) will make a huge difference come springtime. If the area is to be planted in spring/summer, simply pull back the mulch and compost it. In areas that you don't want lawn or shrubs, consider planting groundcovers in place of the annual chore of mulching. Many are low-maintenance and will thrive without extra water in summer. See my earlier post for some recommended spring-blooming groundcovers.
Drainage is no joking matter here. Take a good look at the slope of your property, locate your downspouts and storm drains. Now, where is the water going? Newer homes may have connected the downspouts to a storm sewer connection, but we have seen many that just drain out next to the house, across your treasured plant's roots, washing away bark and soil. The bigger the roof, the more water diverted, and the more potential damage. If you are not handy, consider asking a landscape contractor to look at whether you need French drains or other means to handle runoff.
When planning areas of hardscape (walkways, driveways) homeowners should consider permeable surfaces instead of concrete or blacktop. Selecting concrete pavers on a gravel foundation for your driveway, or even just using gravel as the drive surface, can help to keep vast amounts of water out of our storm sewers and improve groundwater by slower filtering as it moves through layers of rock and soil.
A personal pet-peeve of mine is bark on top of weedcloth, on steep slopes. The first time it rains hard, here comes your 3 inches of barkdust rolling down into the driveway, leaving ugly swathes of uncovered plastic fabric. Yuck. Again, this is a situation for groundcovers. Plant a dense selection and enjoy the view as they fill in; the added benefit is in preventing soil erosion from your steep slope. Plant roots hold soil in place better than anything else.
Obviously this is a big topic, and I am just scratching the surface. Let this be a gentle reminder to plan for rainy winter storms when you have the chance in summer. Happy New Year!
An update: OSU SeaGrant has posted a terrific resource guide for planning/planting "rain gardens." This could provide a beautiful and lasting solution to many homeowners' runoff problems.