By Lynn Welp
Home and Garden columnist | Posted: Sunday, June 15, 2008 12:00 am
With the cool, wet weather this spring, people were asking in jest - "Where is this global warming we're supposed to be having? I'd sure like to see some!" Then came that brief stretch of blistering weather.
Be careful what you ask for. Temperature extremes are all part of the package we call global warming.
What plants should we be planting that will survive global warming? What is the latest research being done through Oregon State University?
I'm afraid the answers aren't clear cut.
No one knows the extent of global warming. Will we be facing wetter winters, hotter summers, droughts, floods, or none of the above? Therefore, when it comes to research, there really isn't any way to test which plants will do well under something that hasn't happened yet.
"So the best answer we in the agricultural field can offer is diversity," says Barb Fick, home horticulturist with the Oregon State University Extension Service Linn and Benton counties.
"Variety is the spice of life and that includes the plant world," she said. "What we don't want is a monoculture."
Plant diversity
A monoculture refers to one species - trees for example - being planted that can become susceptible to disease and insects if they become stressed by drought or more water than they are used to. This is what we are told to expect with global warming.
Thus planting many species will encourage a diverse canopy of trees (and flora and fauna) which will stimulate biodiversity to provide habitat for different species.
This kind of diversity also means no single crop failure can devastate an entire nation - like the potato famine did to Ireland.
The other single most important thing we can do about global warming is protect trees (and plant more). Why? Because by their sheer size alone, trees give off oxygen and absorb the most carbon dioxide of any plant, and shelter other plants from drying wind and sun, thus making them our first line of defense against global warming.
The Douglas fir (Pseudotsuga menziesii) is the official state tree of Oregon, but that may change when climate zones shift. These trees could be vulnerable due to the fact that most trees are generally slow growers. So when they die out in one area, they will take a long time to establish in another.
Hedging my bets, I planted 100 ponderosa pines native to the Willamette Valley several years ago, as I had heard even back then that pines will tolerate global warming better than our native firs.
(They have certainly outpaced some firs I planted at the same time.)
The Arbor Day Foundation has recently completed an extensive updating of U.S. Hardiness Zones based upon data from 5,000 National Climatic Data Center cooperative stations across the continental United States.
Differences between 1990 USDA hardiness zones and 2006 arborday.org hardiness zones reflecting warmer climates can be seen at http://www.arborday.org/treeinfo/zonelookup.cfm.
The different colors represent how much each zone of the U.S. has become warmer since 1990. For example, the pink areas of the map have warmed up enough to change one hardiness zone (e.g. the top half of Nebraska has increased by one zone).
And those changes will affect which trees (and other plants) are right for planting.
Besides diversity, there are other things gardeners can do to prepare for climate change such as sustainable gardening practices.
I've been driving a hybrid car since 2003 to reduce my carbon footprint. But how about someone inventing a hybrid riding lawnmower? Getting a goat to mow for me has been suggested, but … yeah right! However, reducing the amount of lawn I do have is on my list of things to do.
Sustainable gardening practices
Here are some tips for gardeners from the National Wildlife Federation in their publication titled, "The Gardener's Guide to Global Warming" prepared by Patty Glick, a senior global warming Specialist.
1. Purchase solar lights and solar panels for your fountain, garden shed, etc.
2. Reduce the use of gasoline-powered yard tools by using electric-powered, or better yet, human-powered tools. Also consider reducing the amount of lawn you have.
3. Reduce the threat of invasive species - purple loosestrife, Japanese Honeysuckle, English ivy - which threaten to be a monoculture in waterlogged or drought areas.
4. Incorporate a diversity of native plants and thus wildlife into your landscape. http://www.plantnative.com or www.nwf.org/gardenforwildlife for ideas.
5. Reduce water consumption by mulching, installing rain barrels, water early in the day, use drip irrigation, and practice xeriscaping.
6. Develop a rain garden which reduces storm runoff and associated pollution into lakes, streams, and coastal waters. (Now that's an idea for a future story! Got one you'd like to share - let me know.)
7. Compost kitchen and garden waste to cut down on garbage going to the landfill.
8. Establish a "greenroof" which uses special soil and vegetation instead of shingles or tiles to reduce the urban "heat island." For more info go to www.greenroofs.com or plant deciduous trees on the south side of your house to protect your home from the hot summer sun and when the leaves fall off, you get the benefit of sun to warm the house in winter.
9. Plant lots of trees to absorb and store carbon dioxide. One shade tree can absorb about 50 pounds of CO2 per year.
For a full transcript of this article you can go to www.nwf.org/gardenersguide/Gardeners_Guide.pdf
Be sure to choose plants that flourish in regions where summers are hot and dry, and winters are mild and wet.
Mediterranean-style gardening comes to mind. For plants appropriate for gardening in Mediterranean climates worldwide go to http://www.gimcw.org/plants/ or join a local hardy plant society near you http://www.hardyplantsociety.org/links.htm.
Another important tip to protect your plants from drought is to improve the moisture-holding capacity of your soil by digging in organic matter such as compost.
Surprisingly, incorporating compost also helps to aerate waterlogged soil in winter.
Water smart plants
Interestingly enough, using hardy plants found in narrow planting strips between the sidewalk and street or against garage walls) should just about guarantee your garden will survive hot summers. (See sidebar.)
These plants can also survive the wetter winter elements of global warming in soil that has good drainage and aeration. These are considered water smart plants.
I'm not in any way suggesting that everyone rip out the plants you have in favor of those that will tolerate extremes in temperature. I'm just suggesting that when you do want to add something to your landscape - do your homework first.
Each of us can do our part to combat global warming, even if it is as simple a thing as planting a tree.
Survivors
Plants that can survive both the dry summers and wet winters if the soil is well-drained include:
Sempervivum Pekinese and Icicle
Sedum Fuldaglut and S. spathulifolium Carnia
Achillea tomentosa (wolly yarrow)
Agastache rupestris and Blue Fortune
Anenome blanda (wind flower)
Arctostaphylos (many species of manzanitas)
Centaurea Montana (Mt. Bluet)
Cistus (Rock Rose)
Creeping phlox
Dianthus Tiny Rubies
Erodium reichardi Alba and Flore Pleno
Eucalyptus tree (but not all are hardy, my favorite is E. nicholii loved for its small willow-shaped leaves on red stems)
Gaura lindheimeri Siskiyou Pink
Lavendar
Lewisia (Bitterroot)
Liatris spicata
Perovskia Login (Russian sage)
Sea thrift
Veronica Montana Corinne Tremaine and V. liwanensis
Salvia Viola Klose and S. greggi Maraschino Cherry
Penstemon Elfin Pink
Helianthemum Wisley Pink
Gallardia, Hardy geranium Mavis Simpson and Max Frei to name a few.
(Optional: - One of my favorite tough summer annuals (even overwinters in protected spots) is Delosperma cooperi (Ice plant).