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Gardening Column

Gardeners have to pay attention to the cold-zone ratings of plants when they are planning their permanent landscape. These zones refer to the cold extremes woody or herbaceous perennial plants may encounter and survive.

Columbia County is mapped into Zone 8, which considerably broadens the palette of plants that can be tried. Experience over the last 20 years indicate that we probably fall into the gap between Zone 7 (a colder zone) and Zone 8. Often gardeners plant species that test the cold limits and eventually some of those plants will be injured or worse.

Vegetable gardeners are not concerned about winter extremes since they aren’t growing woody material. But they are very concerned about spring, summer, and fall temperatures, especially frost dates and soil temperatures. With vegetable gardens, it is all about early warmth and fast growth.

While individual frost dates can’t be given with precision, we do know averages and these averages can be instructive. For example, we know that in St. Helens, the average last spring frost is around April 15 and the first fall frost is around October 31. Vernonia, on the other hand, has a last spring frost around May 20 and a first fall frost in late September, on average.

Do these numbers predict frost dates with certainty? Of course not. But they do help the gardener plan. There is some evidence that the last spring frost is trending earlier and the first fall frost, later. That may provide a longer growing season for frost tender vegetables.

Geography plays a significant role in gardening. Vernonia is about 600 feet higher than St. Helens which accounts for the shorter interval between frosts. As you travel toward Clatskanie along the Columbia River, the marine influence becomes more pronounced. Temperatures are less prone to extremes of either heat or cold.

Clever gardeners learn techniques to make the most of their climate limitations. Somewhat tender woody plants can be grown along a south-facing house wall to take advantage of winter sun and the cold protection such a wall can offer. It is said that a house wall will radiate interior heat out two feet away from the wall. An overhanging roof line will give additional protection against convection frosts.

The vegetable gardener makes extensive use of greenhouse or cold-frame grown transplants. This technique offers a warm environment to germinate the seeds and develop the plants. As spring arrives, the plants can be moved out into the garden. Protection, in the form of hot-caps or floating row covers, may be needed for a time to protect the transplants.

Both woody and herbaceous plants benefit from soil that drains well in the spring. Vegetable gardeners make raised beds. Once the soil is not saturated with water, it warms up faster. This is very important for vegetables, where root temperatures are as important as air temperatures.

The permanent woody landscape may need improved drainage as well. Tile drains laid out prior to planting can improve water movement. However, the plastic drain tubes need to be laid carefully on a continuous grade to work well. There needs to be enough of a slope to actually carry the water off and there needs to be a place to dump the water. It is not good manners to put it into your neighbor’s yard. Sometimes a low soil berm can provide an area of improved drainage that will allow more water-sensitive plants to be grown.

Old trees need thoughtful care

The trees in our forest and the trees in our planted landscapes have a certain life span. In forests, alders are a relatively short-lived tree while western red cedar, Douglas fir or western hemlock can be very long-lived. The same is true in landscapes. Peach trees are old at 20 while birches can double that. But oaks and maples can live hundreds of years.

As trees age, their photosynthetic and respiration rates slow, they grow less vigorously, tree rings are narrower and dead limbs are more common. Wounds can be very slow to heal.

All of these changes make it harder for the tree to recover from a storm event, insect or disease pressure or poor pruning.

Prune judiciously. Learn what a branch collar is and how to prune so as not to damage it. Remove dead material where feasible and remove competing less valuable trees where your desirable trees are being shaded.

Finally, don’t be afraid to remove a tree if it is clearly heading toward increasing distress.

Have questions?

If you have questions on any of these topics or other home garden and/or farm questions, please contact Chip Bubl, Oregon State University Extension office in St. Helens at 503 397-3462 or at .

Free newsletter

The Oregon State University Extension office in Columbia County publishes a monthly newsletter on gardening and farming topics (called County Living) written/edited by yours truly. All you need to do is ask for it and it will be mailed or emailed to you. Call 503 397-3462 to be put on the list. Alternatively, you can find it on the web at and click on newsletters.

Many Extension publications available online

Are you putting up salsa, saving seeds, or thinking about planting grapes? OSU has a large number of its publications available for free download. Just go to . Click on publications and start exploring.

The Extension Service offers its programs and materials equally to all people.

Contact information for the Extension office

Oregon State University Extension Service – Columbia County


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