Q: Our garden area includes three raised beds, and we usually put pole beans, zucchini, yellow squash and a winter squash in the soil. We try to rotate crops from year to year. Should we be enriching the soil with something now? I’ve heard to add a soil-building conditioner and garden lime. I have composted material that I add to the raised beds in the summer after we pull some crops and before we plant another crop. I have some ready to add now but wonder if it’s better to wait until spring so the rain doesn’t deplete all the good it does. I also wonder if we should get something to cover the raised beds for the winter.

A: Have you ever done a pH soil test on your garden? This is the perfect time to take one. Once you know the pH, you will know if your soil needs lime. You can also buy an inexpensive kit to test for pH, but these tend to be much less accurate than those done in a lab.

Compost is your soil conditioner. It can definitely be applied in the late fall and will release nutrients only after the soil temperature reaches 50 degrees, as the soil organisms go mostly dormant below that temperature.

Having some sort of cover for the garden in the winter is a very good idea. It helps prevent rain compaction of the soil. A cover crop is ideal as it catches any soluble nutrients, protects the surface and reduces weeds. That should have been started in late September, but will probably still catch now. Our favorites include red clover, scarlet clover and fava beans. Wetted newspapers, burlap sacks, leaves (preferably chopped) and even bark chips also all work. These are pulled aside in the spring before planting to allow the soil to warm more quickly.

Pat Patterson, retired Oregon State University Extension horticulturist

Q: Everything in my garden this year has been a problem — corn, green beans, tomatoes, even, believe it or not, zucchini. Even in the high heat earlier in the summer, shaded and well-watered plants failed to thrive.

I have two theories and would like your thoughts, as well as other information you might provide. My first thought is demonstrated by the failure of the corn. Has there been a severe reduction in pollinators? In much of the corn, significant numbers of the kernels failed to mature.

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With respect to other plants that failed to thrive, my thought is that with the interruption in the supply chain due to the virus, old seed stock is flooding the market, resulting in a reduction in vitality and production.

Any insight into these two theories?

A: Vegetable gardeners are experiencing challenging times, and low or imperfect yields may be attributable to a variety of issues. Here are some possibilities:

• fewer pollinators

• extreme heat and moisture swings

• unseen pathogens, particularly in the soil

Some of these are beyond our control; others can be ameliorated if identified. Corn is wind-pollinated, but benefits from close plants so the pollen is concentrated.

You can get a soil test now so that recommended amendments can be applied in the fall and will be available to your plants in the spring.

You can record where you planted this year’s crops, so you can rotate other species there next year.

It’s likely that these steps will provide some effectiveness.

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— Kris LaMar, OSU Extension Master Gardener

Q: We just had to pull down our Himalayan birch due to birch bark borer. Can you suggest a good tree to replace it? It was 5 years old and had just begun providing the only shade in our northwest-facing backyard.

A: When considering what you want to replace your tree with, you might want to go with a native species tree. Natives are better adapted to the Pacific Northwest’s climate and soil, making them generally easier to care for and less susceptible to pests and diseases.

If you are thinking about replacing your birch tree with another deciduous tree, there are several to consider. Red alders and big leaf maples are beautiful, fast-growing trees. The Oregon white oak is slower-growing but is very long-lived. On the smaller size, cascara grow to 30 feet tall and have gorgeous blooming flowers. Madrones are another good choice, but they do shed and should be keep away from areas you would like to keep clean, such as a deck.

There are also good native evergreen choices. Ponderosa pine is a fast-growing and very long-lived tree, while another to consider is the tall and stately western red cedar.

— Jan Gano, OSU Extension master gardener

Ask an Expert is an online question-and-answer tool from Oregon State University’s Extension Service. Submit a question at extension.oregonstate.edu/ask-expert.