Pacific Northwest Gardening Quirks
Our weather has some challenges not found in other summer-dry, "Mediterranean" climate areas. Here's a summary of the problems and how to work with them
Moderate temperatures, with exceptions
Summers are short, with highest temperatures in July and August. And the average highs are in the seventies to low eighties with occasionally spikes into the nineties. Some plants may need more heat, or a situation in a sheltered, sunny corner with protection from the wind.
Winter temperatures are usually moderate, rarely below freezing, but arctic air streaming down from Canada can push lows into the mid-teens or even single digits depending on where you are. These are the days, rarely over a week, that kill less hardy plants.
Winter rains are overly-generous and lethal to some plants
Yearly totals range from around 20 inches in the rain shadow of the Olympics to around 50 inches near Olympia to over 100 on the coast. And soggy ground plus low temperatures kill many drought-tolerant plants
The solution? Well-aerated soil that doesn't hold too much moisture. This could be gravelly or sloped, perhaps amended with perlite or pumice. But, since we're looking for drought-tolerance, it needs to be deep so roots can extend down to the moisture at least a foot to twenty inches down.
Soils are often acid
Both high rainfall and coniferous forest cover produce acid soils, ideal for some plants but not for all. A yearly application of lime can usually solve that problem. Plants that tolerate alkaline soil rarely require it.
Adequate nitrogen may not be available in spring
Some plants love our long, cool springs but drought-tolerant plants from warmer regions may need a few applications of nitrogen to get going. Why? The nitrogen compounds plants can use are produced by microorganism that need warm weather to get started.