It was a mild, springy March, which means it’s time to do some gardening. If you have questions, see Ask an Expert, an online question and answer tool from the Oregon State University Extension Service. OSU Extension faculty and Master Gardeners answer questions within two business days, usually less. To ask a question, just go to the OSU extension site and type one and include the county where you live. Here are some questions asked by other gardeners. What is yours?
Q: We have two raised beds in our yard and I was looking for advice on how to better prepare the soil for this year’s garden. Both garden boxes are approximately 2.5 meters long by 2 meters long by 2 meters wide and 2.5 meters deep. One was built two summers ago and the other was built last summer. Both beds were full of compost when they were built.
Last year, we added some compost to the original box in the garden and mixed it with the soil that was already there. In addition, we don’t add anything else to the soil. Is there anything we should add to these garden boxes to replace the nutrients used by plants in recent years, before planting them this year?
In a garden box, we grew potatoes, peppers, basil, carrots and garlic. The younger of the two had tomato, chive and carrot plants, although the tomato plants took control so that the other vegetables did not survive. – Marion County
A: Vegetables usually look good for a year or more on a new bed, but as they are annual plants, they quickly deplete nutrients, which must be replenished regularly.
The compost is an excellent additive to condition the soil and improve it over time. However, decomposition is a slow process, so the compound is not considered a fertilizer. Many nutrients needed by plants are minerals, such as those found in rocks. Nitrogen is quickly used by plants and expelled from the soil by rain; this is why most fertilizers contain some combination of nitrogen (N), phosphorus (P) and potassium (K).
This does not mean that vegetables need most nitrogen (in fact, too much can result in lush foliage and few fruits); but nitrogen must be replenished more often. Typically, you will see numbers on the fertilizer packaging for the three primary ingredients in the order mentioned above, but many fertilizers also include secondary and micro nutrients that are also needed by plants in small quantities.
In a raised bed, it is difficult to customize nutrients and soil pH for various vegetables. Your best approach is to strive for a slightly acidic soil (pH 6.0 – 6.5). Alternate your vegetables each year so that those from the same family are not grown in exactly the same location, which will also help reduce the buildup of pathogens that can cause disease. Families include Solanaceae (tomatoes, peppers, potatoes and eggplants), the allium group (onions, leeks, garlic) and green leaves.
Ideally, you should do a soil test to determine what your soil is now and then correct or fertilize it accordingly. Many people do not want to test a small garden, but understand that it is a bit like working in the dark without a test.
Good soil has about 3% -5% organic materials in various states of decomposition. This will provide good health and soil cultivation and maintain healthy soil microorganisms. In addition, you will also need fertilizers that can be organic or non-organic (ie conventional or synthetic). Look for a quality balanced fertilizer that has phosphorus and potassium proportionally higher than nitrogen, like 10-20-20.
For more information, see this OSU publication.
In addition, this publication provides an excellent guide for home gardens in general.
One last point I would like to emphasize is that tomatoes are usually better if planted in very large pots, where they will not accumulate other vegetables. You can also stake and prune them so that they grow, not disappear. Read more in this publication. – Lynn Marie Sullivan, OSU master extension gardener
Q: I want to implement no-till and combine it with green manure / cover crops to improve the structure of my soil. However, I am confused about how to get started. My garden has problems with large amounts of weed seeds, clay soil, compaction where I walked and a section where we fight against invasive blackberries and thistle. How can I implement no-till in all of these problem areas? – Marion County
A: You may want to deal with the obvious problem areas first to start the garden and then implement no-till / green manure techniques as soon as you start. Moist and unprotected clay soil is highly prone to compaction, so I would sketch the garden space and decide which areas would be dedicated paths and what the cultivation space would be.
The compaction in cultivation spaces is a short-term problem, so you may want to dig into organic matter when the soil is dry enough to break it using a minimally invasive tool like a fork. You can maintain the soil structure after doing this with the use of mulch or green manure.
I would not allow the weed seeds to discourage you. Remove all perennial and annual weeds as they germinate and you will gradually reduce the seed bank and the number of weeds you will have to deal with. Blackberries are an invasive weed, so, of course, you want them to disappear as well, but they can have the side benefit of protecting, or even improving, the soil structure under the canopy and suppressing other weeds.
Removing them, including the root system, can reveal a soil ready for no-till, with the proviso that there are undoubtedly blackberry seeds that will germinate, requiring continuous weed removal. You do not mention which thistle is involved, hopefully it is an annual species and not Canada Thistle, which is perennial and very difficult to eradicate. Feel free to write back and elaborate on it.
This brief article provides some additional suggestions:
This extension publication provides many additional guidelines, although not specifically on no-till. As I mentioned, feel free to write with questions. – Neil Bell, OSU extension horticulturist
Red clover in Washington County. Oregonian file photo.
P: We grow red clover as a cover crop this winter. We turned over last Saturday. My material from Mestre Jardineiro says to wait three weeks before planting. How critical is this period? What are the disadvantages of planting earlier? Does it make a difference whether we are planting seeds or starting? – Multnomah County
A: In this Washington State University Extension publication, here, in the section on closing a cover crop, is “Residues from newly finished cover crops can inhibit seed germination, including the germination of desirable vegetable seeds. Waiting to plant vegetables for three to four weeks after the cover crops are finished usually improves your establishment. “
The publication of the OSU extension “Growing Your Own” provides schedules for planting. The soil is too cold and wet for most of the planting so early, so maybe hoping it won’t get in the way of your garden plans. – Jacki Dougan, master gardener for the OSU extension