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Friday, February 23, 2024
Feb. 23, 2024

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Gardening with Allen: More to plants than hardiness

By , Columbian freelance writer

I understand that a new hardiness zone map has been released. Has our hardiness zone been changed?

The new 2023 Hardiness Zone Map is based upon average weather for the 30-year period 1991 to 2020. So in my opinion it is still a little out of date because the weather has warmed more quickly in the last few years. It shows that Vancouver and most of Clark County is in hardiness zone 8b, which is a half-zone warmer than the previous map. This translates to an average winter minimum temperature of 15 to 20 degrees. Higher elevations have lower zone ratings.

This means that we should be able to plant any plant with a zone rating of 8 or lower and expect it to live through the winter. In my opinion we could safely plant many zone 9 plants, also because of more recent warming.

However, hardiness is only one factor for selecting plants for the landscape. These factors include: sun or shade tolerance, soil pH, drought tolerance, and mature size. Most perennial and hardy plants have sun/shade tolerance and mature size on their labels. It requires more research to find soil pH preference and drought tolerance.

Most full-service nurseries and garden stores offer plants that are adapted to our climate, including these last two factors. Other stores that offer plants only during a limited planting season sometimes have plants which are not adapted. For example, plants which are not adapted to our acid soils. Drought tolerance is something we are still learning about. As our climate becomes dryer, we will find out which plants we have used for years are adapted without regular irrigation.

In our climate we should be planting evergreen shrubs that do not lose their leaves in the wintertime. Why plant something which is bare of leaves for half the year?

I have written repeatedly about the importance of selecting plants that fit the physical location where they are planted. Even professionals make the mistake of planting plants that look very nice when planted but soon grow into each other and extend above and beyond the space where they were planted. Take the time to get the tape measure out and measure the spaces where you want to install plants. This should also include the height of windows you do not want to block with growth. Then check plant labels for the mature size. The mature size is listed as the expected size after 10 years of growth. Some plants outgrow this size, especially in the Pacific Northwest.

Sun and shade tolerance are also important. Most sun-loving plants will do fine with half a day of shade. Shade-loving plants will often grow fine with east sun exposure, but will burn with south or west exposure for even part of the day.

Columbian freelance writer