Soil fertility

Broccoli, Beets, and Boron – Updated

8 March, 2019 by amygwh Leave a Comment

Soils in the region where I live are short on the mineral boron, an essential plant micronutrient. The University of Georgia soil lab doesn’t measure boron levels in its routine test for garden soil, but it does include a recommendation to add some to a home vegetable garden. This is the recommendation:

“Apply 1 tablespoon of borax per 100 feet of row to broccoli and root crops such as turnips and beets. This can be applied by mixing the borax thoroughly with approximately 1 quart of soil in a container and then applying the mixture along the row; or it can be mixed with a quart of water and applied to the soil in solution.”
University of Georgia, Soil Test Report, basic soil test for Home Vegetable Garden, 2018

What is a micronutrient?

Boron is one of several micronutrients that plants need. The micronutrients are needed in tiny amounts, but they are essential for plant growth. Other micronutrients include copper, iron, and nickel, among others.

For boron, the difference between not-enough and too-much is a pretty narrow range, according to K. Kelling at the University of Wisconsin and Ron Goldy at Michigan State Univ. Extension. This means that great care must be taken to not use too much.

How does boron help plants?

Golden beets growing in the garden - beets are a crop that need a little more boron than others. — Golden beets growing in the garden – beets are a crop that need a little more boron than others.

UMass Extension, Amherst, says that boron “is required for many different aspects of plant cell functioning, including protein synthesis, development of cell walls, carbohydrate metabolism and sugar transport, pollen growth, fruit set, and seed production.”

Sounds important, to me!

What happens when plants don’t get enough boron?

The UMass information about boron deficiency lists these possible effects of too-little boron:

“stunting and distortion of the growing tip”
“brittle foliage and yellowing of lower leaf tips”
reduced flowering
reduced fruiting
distorted fruit
“brown heart” (mushy brown centers) in root crops like turnips and rutabagas
hollow stems in broccoli and cauliflower
brown or otherwise discolored curds on cauliflower

Kelling’s Soil and Applied Boron publication adds that cabbages that are low on boron may show an “internal breakdown of head”.

Which plants need the most boron?

Some vegetable crops need more boron than others.

Broccoli growing in the organic home garden.

Ron Goldy’s U Michigan publication lists crops and their relative need for boron. The high-need vegetables for boron he includes are these:

broccoli
cauliflower
celery
table beets
turnips

How can I provide boron to my garden?

One way to add boron is to follow the instructions on the UGA soil test report, to mix a tablespoon of borax in water or with soil and to spread that across a 100-foot row of garden, especially in areas where higher-need vegetables are growing. If your garden is not in rows, or is smaller, it will need less borax.

The borax you will need is in the laundry section of your grocery store, in the box of 20 Mule Team Borax. This should be fine for organic gardens, because it is a mined mineral.

You will need to be careful with this product, though, because it is easy to use too much. Do not apply the boron every year without having the boron levels tested at a reliable soil lab.

If you prefer to use another product, one that contains many micronutrients, including boron, to safely fill any gaps, try kelp meal. It is much more difficult to use too much boron when using kelp meal, because it is a much less concentrated source of the micronutrient. There is enough, though, to help your plants. Just follow package directions for safe use in your organic home garden.

Georgia isn’t the only state with low-boron soils

The 20 Mule Team Borax company notes that boron will be at low levels in soils that are sandy, or acidic, or that are low in organic matter (like Georgia clay!), or that are in areas of high humidity.

The company has found that low-boron levels are a common problem in soils east of the Rockies and in the Pacific Northwest. The middle of the country and the Southwestern region mostly have sufficient boron.

To learn more about soil fertility in organic home gardens, read my posts about potassium sources, soil pH, building good garden soil, and side-dressing your garden crops.

Good Garden Soil

4 January, 2019 by amygwh Leave a Comment

Small farm with red clay soil in north Georgia produces a lot of good food.

Several gardening books I’ve read include the note that good garden soil is a sandy loam, rich in organic matter. My yard’s soil is naturally a massive gob of red clay — like in the nearby photo — not at all what is recommended.

Red clay is actually not all bad. It holds nutrients much better than sandy soil, so it doesn’t need as much fertilizer. It also holds water — sometimes too well! — which means it is slow to dry out. When it does get dry, it becomes brick-hard and tough to dig.

Plants benefit from the nutrient-holding and water-holding capacity of clay soil. The problem is that the clay compacts and does not allow roots to move easily through the soil, and it doesn’t have good air spaces (which roots need).

Not every yard in this area has such dense red clay as mine. When we first moved here (in 1990), and for years afterward, an older gentleman in Kennesaw grew roses, lots and lots of roses, out near the road on Cherokee Street.

I stopped to talk with him once, when I saw him out tending his roses. He said that a friend brought him a truckload of oak leaves to use for mulch each year, but that his yard had naturally good soil. That comment stunned me into speechlessness for a moment — my experience was so different!

Most people I talk to around here have soil like mine. This may be why so many new gardeners use raised beds filled with soil mixes that don’t include clay.

My gardens, though, are not in raised beds. They are in the ground, in that red clay. I add amendments like compost (from my yard) and soil conditioner (from a garden center) to increase the organic matter and microbial activity. The amendments make the clay soil a more welcoming place for the roots of my crops.

How to create good garden soil from red clay

A recommendation from Cooperative Extension’s “Ask an Expert” page for improving clay soil, is below. The picture of the compost bin nearby, though, is a clue about at least one important amendment.

Here is the Extension Expert’s recommendation:

Choose an organic soil amendment like composted yard waste, rotten leaves, or well-rotted manure (make sure any composted manure does not contain residual herbicides!). Material that is well-rotted will not smell unpleasant; it will smell like the earth.
Spread a 3 to 4 inch layer of your chosen amendment on top of the clay soil; work it down into the soil about 6 to 8 inches.
After the compost has been worked into the soil, you can spread an inch or two layer of sand on top and gently spade it in.
Before planting in spring, lay on another 2-3 inch layer of compost and work it into the soil, about 6 to 8 inches down (the depth of a shovel blade).

Walter Reeves, The Georgia Gardener, has an updated article on Soil – Bed Preparation that suggests bagged soil conditioner as an alternate for compost. His article also suggests adding Permatil to the mix, to keep the clay soil looser, as the composts and soil conditioner decompose and disappear.

Permatil is expanded shale, and it creates air spaces in the soil. I have added a similar product to part of my upper garden, an area I don’t re-amend as often as the veggie area because it has some perennials (permanent plants).

If you can’t find Permatil but are interested in trying something similar, look for Espoma’s Soil Perfecter, bits of kiln-fired “ceramic mineral” that works in a similar way to open up air spaces in the soil.

Nutrients and pH?

The Extension recommendation above does not address soil pH (acid level) or fertility/nutrients. The Expert who answered the question may have assumed that everyone will know to send a soil sample to their state’s soil lab (Georgia’s is at UGA, in Athens) through their local Cooperative Extension office.

If you are not sending a soil sample to your state’s soil lab, consider buying a pH test kit (see my article on Soil pH and Garden Success for more information). For fertility, if you don’t have a soil lab recommendation for fertilizer, choose an organic-approved garden fertilizer and follow the package directions. To learn more about nutrient sources for your garden, check out my articles on Potassium Sources for an Organic Garden and on Fish Emulsion Fertilizers.

Dig soil when ground is not soggy

You will know your clay soil is dry enough for digging when you can squeeze a handful of it and it breaks up into bits. You should not be able to roll it into the kind of snake-shapes that can be coiled to make pottery bowls.

Clay soil needs to be not-soggy at digging time, partly so you can get the clay to let go of your shovel and partly so it won’t reform into giant, brick-like clods when the lumps finally dry. Digging in wet clay soil also causes it to compact, making it lose the air spaces that are vital to healthy plant roots.

Winter is a great time to work on improving garden soil or to create new planting beds. Here in the South, we have some pleasantly cool afternoons mixed in with the cold ones, which means we have good opportunities for working outdoors.

Right now, though, the ground is squishy under my feet when I walk in the yard. I just need to wait for the rain to stop and the ground to get drier.

Soil pH and Garden Success

15 December, 2018 by amygwh Leave a Comment

When a garden hasn’t been doing well, one of the first conditions to check is the soil’s pH, its acid-alkaline balance. The pH scale goes from 0 to 14; 7 is the neutral pH, measurements below 7 are acidic, and measurements above 7 are alkaline.

For reference, distilled salad vinegar has a pH in the range of 2 to 2.5 (acidic), and cold-process soap has a pH in the range of 9 to 10 (alkaline).

Soil pH influences how well plants can take in nutrients from the soil, so getting a garden’s soil into the best pH range for your plants will help them be healthier and more productive.

What is less well-known is that correcting a pH that is either too high or too low takes time. Testing soil pH should be done now, or soon, for gardens that have not done well in the past year.

What pH is good for gardens?

Blueberries will be ripe beginning in mid-to-late June. — Blueberry plants prefer a soil pH near 5.

Most garden veggies need a soil pH of between 6 and 7. Where I live, northwest of Atlanta, the natural soil pH is lower than that range — it is naturally acidic. With that acidity in mind, many people here routinely add lime to their lawns and gardens without checking the soil pH first, and end up with a soil pH that is too high.

When I worked at the local Extension office and managed the soil samples that went to the soil lab at University of Georgia (UGA), it was not unusual to see some samples with soil pH around 5, but others with pH higher than 8. Those higher pH soil samples were from lawns and gardens that had been limed pretty much every year.

Once, a friend who decided to plant blueberries in the space where she had originally kept a vegetable garden sent a soil sample in to the lab at UGA. The lab found that the pH of her soil was 7. This pH level was not a surprise because she had been spreading ashes from her fireplace on the garden. Wood ashes are a good source of potassium, but they raise the soil pH.

For many veggies, a soil pH of 7 is fine, but the blueberries she hoped to plant in that space prefer a pH closer to 5. That soil needed some work before it would make a good home for blueberries.

How can I find the pH of my garden soil?

Example of easy to use soil pH test kit for home gardeners.

The most reliable method of finding your garden’s soil pH is to send a soil sample to your state’s soil lab. Call your local county Cooperative Extension office to find out how to take a representative soil sample, how to package it, and the lab fee for this service.

Another option is to purchase a pH test kit at a local garden center. One I have used (pictured nearby) includes a container with color chart for comparison, capsules of pH-indicator-powder to add to the container, and instructions.

The basic instructions for this kit, and others:

put a tiny bit of garden soil into the container
add the indicator powder
add water up to a line near the top
put the lid back on the container, then
mix the parts together by shaking the container until color develops.

You find the pH by comparing the color of your sample to the chart on the front of the container.

Soil sample in pH test kit with water and indicator powder, to read the soil pH. — Sample in pH test kit shows pH of soil in my upper flower bed to be about 6.5.

How to lower a too-high soil pH

The UGA soil lab sent information to my friend about how much aluminum sulfate (the cheapest option) to add in order to bring the pH down to a better level for blueberries. If you know that the pH of your garden soil is too high, but don’t have a lab-recommendation for how to lower it, the amount of elemental sulfur (my preferred option) needed can also be found in a table by Clemson University Extension, in its Changing the pH of your soil publication.

For a soil pH that is only slightly high (about 0.5 higher than the desired level for your plants), one of my county’s former Extension agents used to recommend mixing sphagnum peat into the soil as a quick fix. Iowa State University Extension suggests other amendments that can lower a too-high pH, including “elemental sulfur, aluminum sulfate, iron sulfate, acidifying nitrogen, and organic mulches.”

There is a note, too, that a very high pH (over 8) is hard to bring down. When the local Plant-a-Row-for-the-Hungry garden (one of my volunteer groups/projects) was at a location that had a high-pH soil, we added the recommended amount of sulfur several years in a row before the pH started to come down.

How to raise a too-low soil pH

The Iowa State University publication How to change your soil’s pH includes a table showing how much ground limestone will be needed to raise soil pH. If you have hydrated lime handy, and think it might be a “quicker fix” for a too-low pH, please don’t try it. The risk of raising the pH too high with this product, by accident, is large. Lowering the pH after over-liming is difficult and can take a long time. Use ground limestone instead of quick lime or hydrated lime.

It takes more lime to raise pH in a clay soil than in a sandy soil. In general, according to the table in the Iowa State publication, for 100 square feet of clay-soil garden, it takes 5 to 6 pounds of limestone mixed into the top six inches of soil to raise the pH by 0.5.

When is the best time to adjust the soil pH?

For my friend’s blueberries, the UGA lab report recommended that the bushes shouldn’t be planted until 6 months after applying the sulfur. If she added the sulfur in October, that means blueberry-planting should — for best effect — wait until April. That is pushing the boundary for good planting time for woody plants like blueberries; as spring progresses and the weather warms, newly planted bushes are less likely to do well. They need time in the soil for their root systems to become established before being stressed by the heat of a Georgia summer.

What this means is that soil testing should be done now, if it hasn’t already been done, so adjustments to pH can be made soon enough to benefit plants that will be planted in spring.

What soil pH is best for my plants?

An article by Lewis Hill, published in Robert Rodale’s The Best Gardening Ideas I Know (1983) includes a list of some garden plants and the pH ranges they prefer. I’ve pulled some of the food plants from his list to post here:

pH 4 to 5: blueberry
pH 5 to 5.75: blackberry, grape, parsnip, plum, potato, pumpkin
pH 5.75 to 6.5: bean, citrus fruits, cowpeas, currants, gooseberry, oats, pepper, rutabaga, rye, squash, strawberry, tomato, turnip
pH 6.5 to 7: apple, beet, broccoli, buckwheat, butternut, chicory, chives, cucumber, eggplant, endive, kale, leek, muskmelon, onion, pea, peach, radish, raspberry, rhubarb, spinach, watermelon, wheat
pH 7 to 7.5: alfalfa, asparagus, barley, cabbage, carrot, cauliflower, celery, lettuce, nasturtium, parsley

This list may help other gardeners in planning what to plant where, but it is comforting to remember that plants will still grow and produce in soil that is slightly outside their preferred pH range.

This is lucky, since most of us grow many of these plants mixed all together in our gardens. However, for peak production, planting in soil that is actually the preferred pH for each crop works best.

Succession planting with preferred pH for each crop in mind

When I plant Irish-type potatoes in the spring, I will have added some sphagnum peat to their soil to bring the pH down a bit, but not all the way down to 5. Knowing the pH preferences of other crops helps me know what to plant after the potatoes in that space. For example, cabbages in that space would likely be a total bust, because their pH preference is so much higher (7 to 7.5!).

After potatoes are harvested, a better option than cabbages would be to let a nearby vining crop, like melons, sprawl across that space. Another option would be to plant a crop there that prefers a lower pH range, like beans or cowpeas that thrive at pH 5.75-6.5.

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