A Gardener’s Diary: preventing blossom-end rot

Jocelyne Sewell is a longtime gardener and gardening columnist with The Morning Star in Vernon

After I wrote a recent column about tomato bottom-end rot, I received some feedback which led me to find out more information on this topic from three different sources.

Blossom-end rot is caused by numerous factors, including magnesium or calcium deficiencies, irregular watering practices and over fertilizing, which can interfere with a plant’s ability to absorb calcium from the soil.

Epsom salt contains about 10 per cent magnesium and 13 per cent sulfur. Magnesium is vital for seed germination, chlorophyll production and healthy cell wall development.

Plants need sulfur to produce vitamins, enzymes and amino acids.

Informal garden studies performed by the National Gardening Association have shown that epsom salt may encourage bushier growth, larger harvests and reduced risk of blossom-end rot.

If you’d like to try using epsom salts to prevent blossom-end rot, combine one tablespoon of epsom salts with one gallon of water, suggests the gardening association.

Apply this solution as a foliar spray immediately after planting, when the plant first produces flowers and when young tomatoes appear.

To reduce the risk of blossom-end rot, water tomato plants frequently so the soil stays evenly moist — never soggy or completely dried out.

A natural mulch, such as untreated grass clippings or weed-free straw, can also help maintain even soil moisture.

Epsom salt seems to be most effective on acidic soils that may have magnesium deficiencies, notes the Colorado State University Extension.

It’s best to conduct a soil test before you add any amendments to your soil.

If blossom-end rot is caused by a calcium deficiency, adding epsom salts can actually exacerbate the problem because excess magnesium in the soil can interfere with a plant’s ability to absorb calcium.

In this case, adding limestone, which contains calcium, is a better solution, asserts the Clemson University Cooperative Extension.

A study done by North Dakota State University — it’s time to debunk that myth — found Epsom salt doesn’t stop blossom end rot, it leads to more of it.

Blossom-end rot is caused by a deficiency of calcium. Epsom salt contains magnesium sulfate — no calcium at all. Adding epsom salt to the soil may create more rot since magnesium and calcium ions compete for uptake into the plant.

The more magnesium in the soil, the less chance that calcium will be absorbed. So what can we do to prevent blossom end rot?

Don’t focus on the soil. Most soils in North Dakota have plenty of calcium.

Focus on watering. The uptake of calcium depends on the uptake of water.

Irrigate regularly. Avoid the extremes of waterlogged soil and droughty soil.

Mulch to maintain consistent levels of moisture in the soil. Cultivate shallowly.

Don’t damage the roots of your vines. We need these roots to absorb calcium.

Avoid overfertilization, especially with ammoniacal nitrogen fertilizers (ammonium nitrate and most complete fertilizers such as 10–10–10).

Ammonium competes with calcium for uptake. Calcium nitrate is a better choice.

Vines should be green but not lush. Lush vines are more likely to suffer rot since actively growing leaves take calcium from the vine before the fruits get it.

As a general rule, don’t sidedress a vine until after its first fruits set. Pinch suckers. Calcium sprays might (or might not) help.

Mix four tablespoons of calcium nitrate per gallon of water. Spray fruits, not leaves, two to three times a week. The key time is when tomatoes are dime-sized or smaller.

Now you can take your pick from these solutions I’ve mentioned. Many times, I don’t know what I am doing but I like the way I do it and will keep doing it.

I just picked 20 pounds of perfect tomatoes. The only bad one in my garden is Roma which can be replaced by many other good paste tomatoes.

Jocelyne Sewell is an avid gardener in Vernon. To reach her, call 250-558-4556 or email jocelynesewell@gmail.com.

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