People often think it’s hard to grow warm season plants (e.g., tomatoes and peppers) on the North Olympic Peninsula because of our short growing season. That’s a misconception. The growing season in Western Washington is fairly long; the problem is that it’s also cool.
A cool growing season is a problem for plants that need accumulated heat in order to grow, flower, set fruit and successfully ripen.
Growing Degree Days (GDD) is the measure of the heat plants need to successfully mature, especially fruits and vegetables. A GDD unit is the difference between the average air temperature of any given day and a plant’s base temperature, the temperature required to grow.
GDD is not a layman’s calculation. Fortunately, Oregon State University Small Farms Team is developing a vegetable degree day website called CROPTIME (smallfarms.oregonstate.edu/croptime) that provides GDD for many crops.
However, a GDD calculation is not needed to know what steps can be taken to heat up the garden and to improve the ability to grow warm season crops. Two important steps are: plant selections and the manipulation of the microclimate.
Picking plants, climate controls
First, select plants and seeds that were developed for the area or sourced from growers in a similar climate. Selecting varieties that have shorter “days to maturity” will increase the chance to reach full maturity. This information should be on the seed package. Starting seeds indoors or purchasing starts from a locally sourced grower is another important strategy.
Next, for the most successful growing warm season crops in a cool area, the microclimate can be modified. There are five major components to microclimate: topography, soil, structure (natural and man made), water and vegetation, the first three being the easiest to manipulate.
Topography is multifaceted and can include elevation, sun orientation, slope and even wind. For the purpose of warming a garden it’s important to choose a location with full southern exposure with a natural or fabricated wind screen. It’s also important to identify and avoid low-lying areas (cold sinks) and areas with poor drainage.
Elevation is an aspect of topography not easily adjusted. Frost dates and winter temperatures are affected by as little as a 500 foot increase in elevation. For growing at higher elevations it’s always important to keep an eye on the weather and be prepared to cover tender plants.
Soil is important because in order for some plants to germinate, emerge and start to grow in spring, the soil must be warm; warmer for some like tomatoes than for others like spinach, which grows well in cool weather. Soil warming is affected by the direct absorption of the sun’s energy but is also greatly affected by the soil structure and moisture capacity.
Wet soil absorbs the sun’s energy but loses much of the early warmth due to evaporation.
Compacted or heavy clay soils will be much slower to heat up, hindering the growth of heat loving plants. A later winter and spring rains can delay the warming of the soil.
There are ways to encourage the warming of soil by adding amendments to improve structure and/or raised beds to improve drainage. According to Oregon State Extension, using clear plastic over a garden bed will help increase soil temperature.
A physical structure can help alter natural topography to your benefit. Locating warm season beds along a south-facing structure or wall mass can increase warmth, especially if the surface absorbs and holds heat. Of course, a greenhouse is the ultimate and more permanent structural modification. But less costly measures such as using row covers, cold frames or a simple hoop house can be useful as well.
As vegetable starts start appearing in garden centers and plant sales, it’s important to understand the importance of warmth when planting out warm season crops. Early planting before the soil warms can result in poor performance.
Susan Kalmar is a Clallam County Master Gardener.
Raise ‘em up
Raised beds are a great way to grow plants where the growing season is cool. The soil will warm up faster and dry sooner making it easier to get your plants off to a good start. Keep in mind, they will also require more frequent watering in the summer and fall.
Plant sale set for May 6
It’s time to put those chilly April blues behind and embrace the warmer temperatures of springtime.
Get your garden going with plants, saplings, perennials, vegetable starts and more at the Master Gardener Foundation of Clallam County Spring Plant Sale, on Saturday, May 6, at the Woodcock Demonstration, 2711 Woodcock Road. Check out items from 9 a.m.-12:30 p.m., or take advantage of the half-price sale from 1-3 p.m.
Get to now where your food comes from, be a “localvore” and grow produce from veggie starts including tomatoes, peppers (sweet and hot varieties), salad greens, squash, zucchini and more. Invite pollinators to your yard year after year and purchase native flowering perennials like snowberry, Pacific ninebark, red flowering currant, thimbleberry, twinberry, mock orange, ocean spray and red-osier dogwood.
Or, add some pop to some favorite recipes and choose from a wide variety of fresh herbs like rosemary, sage, parsley, thyme, mint and oregano. Buy a red cedar, grand fir or Douglas-fir and enjoy the bird song and shade these trees will bring for decades.
Explore an expanded houseplant section with plants such as aloe vera, holiday cactus, spider plants, inch plants, purple oxalis and add cheer to interiors.
Clallam County Master Gardener volunteers who will be on hand to give free advice and answer questions about purchases.
Stop by the garden’s General Store for gardening gifts and gently used tools and supplies.
Petals & Pathways Garden Tour tickets will also be on sale for the early bird price of $15.
Our offerings have been lovingly fussed over by our own Clallam County Master Gardener volunteers who will be on hand to give free advice and answer questions about purchases.
All proceeds from the sale will help to maintain the 2.4-acre Woodcock Demonstration Garden and the 5th Street Community Garden demonstration in Port Angeles. Funds from the plant sale will also support the numerous Master Gardener community services such as the Youth Enrichment Program (YEP) in local schools, as well as Green Thumb Education Series and Digging Deeper presentations.
For more information, visit clallammgf.org.
