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Don Kinzler, Published October 12 2012

Hortiscope: Watering, calcium both related to end rot

Q: I read your article about blossom end rot on tomatoes. All the articles I have read say to give the tomatoes some calcium. It does work, so the rot has nothing to do with watering. I figured a man in your job would know better than to say it is the watering. (email)

A: Blossom end rot is a condition that results from insufficient calcium reaching the developing cells between flower fertilization and fruit development.

The insufficiency often is the result of an underdeveloped root system that is unable to mine sufficient calcium from the soil. It is stimulated by wide fluctuations in water delivery. It could be watering followed by a dry spell and then a heavy application from a rain event or overzealous irrigation that flushes into the developing cell tissue, causing the rupturing of the developing cell walls. This leads to the rot we see on the blossom end of the fruit.

Because the water gets there before the calcium does to be a part of a stronger cell wall, the BER develops.

It also can be caused by root damage from too aggressive cultivation around the base of the plants.

BER is tied in with some tomato varieties being more susceptible to this abiotic problem than others.

In my garden, the paste tomatoes used in making salsa tend to be more susceptible to BER.

In a nutshell, you are correct in saying that BER is due to a lack of calcium in the blossom end cells.

However, the most common cause of it is in watering fluctuations. I suggest planting tomatoes deeply and mulching them with peat moss to mitigate any watering aberrations.

If I am wrong, then I’m in pretty good company. BER information is available at http://tinyurl.com/9gsnlvl.

Thanks for allowing me to clear up any confusion on this annually occurring problem with our tomatoes and other members of the nightshade family.

Q: I have a question for you about a crown of thorns plant.

I have a plant that has been in my family for about 50 years. Unfortunately, some leaves have been turning yellow and falling off or I pull them off.

I don’t water it that often. The plant gets bright but not direct light during the day. On the top of one leaf, there is a small, black, shiny dot that is slightly raised. It is about the size and shape of a grain of sand.

I tried to wipe it off, but it seems to be adhered to the leaf.

On another leaf, there are four yellow spots with small, light brown spots that are slightly raised. The yellow circles seem to have sheen to them.

Do you have any idea what this is? I’m so worried that it will keep losing leaves and die. I don’t know what to do. (email reference)

A: Based on your description of the problem, but counter to what you say, it sounds like your problem is overwatering. My suggestion is to repot the plant using fresh soil. Make sure the pot drains well.

Insects typically don’t bother corn of thorns plants. Diseases also are rare, so insecticides or fungicides are not recommended.

Keep in mind that it is a natural occurrence for this plant to drop leaves as the days become shorter going into winter. The plant will releaf the following spring as sunshine increases.

Q: My lilac tree is not flowering as much as it used to.

My neighbor tells me I need to cut out the sucker stems around the tree to make it blossom more. Is this the right move? (email)

A: That would be a good start. Give it a shot and see if the blooming improves next spring. Keep in mind that pruning the main stems at this time of year will remove the potential flowering parts of the plant.

If needed or desired, lilac pruning should be done shortly after the plants have finished blooming.

Q: I usually deadhead all my roses. However, I read somewhere that I should leave the spent roses on because they benefit the plant.

Should I go ahead and deadhead the roses or wait until I cut them back for the winter? (email)

A: Go ahead and deadhead them. I cannot think of a reason why leaving the spent flowers on the plants would do them any good.

Cut them back to 10- to 12-inch stubs and cover with leaves or potting soil for the winter.

Q: What would your opinion be on what is happening to my ponderosa pines?

They have dropped all their needles except for the upper third of the trees. Is this needle cast or a result of the past few years of stress? Is there anything that can be done to save the trees?

I’m also sending a picture of a young spruce tree that is turning yellow and dropping needles. I’m wondering if I should pull it and start over. (email)

A: The pines appear to be behaving normally.

They are dropping their interior needles because of the hot and droughty conditions that we had these past few months.

They do need to be hydrated going into winter, so I’d suggest laying a hose under their canopy spread and give them a good, complete soaking until the ground or water source freezes. Otherwise, they will be dead for sure next spring.

The spruce is beyond hope, so yank it out.

Q: I have a question for you on trimming my fern peonies. They get doggy looking during the summer, so I’m always tempted to cut them back at that time, but I don’t.

However, after the past two evenings of frost, I cut them back to the ground. When is the correct time to cut them back?

Also, we trimmed our apple tree yesterday after two frosts. Is that too soon?

We are looking for an apple tree that has the hardiness of a Haraldson apple but has a thinner skin and a larger and sweeter apple. We tasted one at our friend’s home. Unfortunately, he cannot recall the hybrid he planted five years ago.

Are you familiar with the characteristics I am speaking of, and can you recommend an apple tree to us? (email)

A: You did the right thing by cutting back your peonies, although it wasn’t critical for you to do it right away.

The apple tree pruning is acceptable, but a March pruning would have been better. I don’t think the tree will suffer any consequences for this.

Look for honeycrisp apple trees. They are ready to pick now. As the name implies, honeycrisp produces a sweet apple. It should be available at most local garden stores.

Q: We transplanted some spruce trees around the perimeter of our property three years ago. This was the first summer they grew vigorously.

However, I fear the spruce trees are suffering from our prolonged dry spell. Some are dropping brown needles. The trees that get the most sun are dropping the most needles. The ground around the trees is dry and cracked.

How much should I water them to protect them for the upcoming winter?

Do you recommend Wilt Pruf? When would we treat them?

Can the south side of the trees be treated or should it be applied to the entire tree? (Moorhead)

A: Don’t use anti-desiccants. Get a hose going under these trees as soon as possible, and you still might be able to save them.

Give them a soaking once a week. However, the initial watering should be very thorough.

Some needle drop is to be expected. As long as the current season’s growth remains, they should make it. Keep the water going until our region freezes up. Hydrated trees stand a better chance of making it through our winters.

Q: Why do my cabbages have flowers? (email)

A: Cabbage is a biennial that normally doesn’t flower unless a sufficient cold treatment causes a hormone shift that pushes it into the reproductive stage.

Where the winters are not so severe to kill the plants, they will bolt the following spring and come into flower.

Your plants must have received some external stimulus from nature or someone is applying a flowering hormone to the seedlings that pushed them into the reproductive stage. Don’t expect any cabbage heads from those that are producing flowers.

Q: Three years ago, I purchased three yew shrubs that I planted in front of our house. They are doing well, especially this year.

When is the best time to trim them? I know they need trimming, and I desire to do the right thing at the right time. (email)

A: Yews are pruned in spring or early summer. This late in the summer is not recommended because it may stimulate new growth that might not harden off before winter.

The yew is one of the most responsive plants to pruning. It often is formed into interesting topiary shapes by gardening artisans.


To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or email ronald.smith@ndsu.edu.

For answers to general horticultural questions, go to www.ag.ndsu.edu/horticulture.