Dear Master Gardener: The tops of my tomatoes are yellow. Why?

Answer: Gardeners are experiencing two common physiological disorders right now — yellow shoulders and blossom end rot. Yellow shoulders occur when the fruit near the stem doesn’t ripen properly, resulting in a yellow region. Scientists believe there could be several causal factors with one of them being high heat over 90 degrees and another being a shortage of potassium in the soil. Some tomato varieties are more susceptible to it than others. Leaving the fruit on the vine to ripen longer will not improve the condition.

Tomatoes with blossom end rot have a tan to black flattened spot at the blossom end of the fruit and can appear during any stage of development. It is most commonly seen when the fruit is one-third to one-half grown. This disorder is caused by a calcium deficiency in the tomato plant. It doesn’t necessarily mean that there is a lack of calcium in the soil — it means the plant is not taking up calcium. This typically happens due to inconsistent watering.

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Dear Master Gardener: My bell peppers have tan areas that are soft. Why is this happening?

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Answer: It sounds like sunscald on your bell peppers, which happens when the fruit on the plant is exposed to both high temperatures and intense sunlight. Although peppers need very warm temperatures to grow, the high heat will break down the pepper tissue while the sunlight will cause adverse chemical reactions. Consequently, this causes tan areas on the exposed areas of the fruit. If plants experience drought conditions (which we have been experiencing this summer) and don’t receive adequate water they won’t develop thick foliage that will shield the fruit from direct sun.

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Dear Master Gardener: I have been stung multiple times in the past week from hornets coming from ground nests. What should I do?

Answer: Oftentimes ground-nesting yellow jackets are discovered quite painfully while weeding gardens or mowing the lawn. You also know they are present from the steady stream of wasps flying back and forth. The best control is to apply a single application of an insecticidal dust directed at the nest opening. Liquid products are not recommended. According to Michigan State University, insecticidal dust works well because the wasps pick up the dust as they enter the nest and carry it to the rest of the nest, contaminating the entire nest. They suggest doing this treatment in the early morning. Following the measurement directions on the insecticidal dust (Sevin 5 is a good option) quickly dump the dust in the opening and run!

Related: Ask the Master Gardener: Tips for fending off a garden-destroying fiend

Dear Master Gardener: I have quite a crop of berries on my black chokeberry shrubs. What can I do with them all?

Answer: Aronia melanocarpa (black chokeberry) is a Minnesota native shrub that is very tolerant to a variety of soil textures, pH levels and moisture conditions. Not only does it make a great landscape shrub with its showy white flowers in spring and vibrant fall foliage, it can be used as an edible fruit crop. The berries are too astringent to eat raw; however, this high-antioxidant fruit can be used to make jams, jellies, syrup, tea, juice, and wine. This shrub is also a wonderful food source for birds.

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Dear Master Gardener: My niece is using hydrangea flowers to decorate her wedding cake. Aren’t they poisonous?

Answer: Hydrangea flowers are sometimes used as a wedding cake topper which could lead people to believe they are edible. They may be beautiful, but they have a dark side. The flowers (buds and leaves) contain a cyanogenic glycoside called hydrangin, which converts to cyanide. Reports of poisoning from hydrangeas are rare, but the plant is mildly toxic to humans, dogs and cats and will cause stomach upset if ingested.

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Dear Master Gardener: I have little white worms in my houseplant soil. What are they and how do I get rid of them? I think I overwatered my plant which may be the cause.

Answer: Since you think you overwatered your plant, you probably don’t have worms, but have fungus gnat larvae. Move the plant outdoors and allow the soil to dry out, but not to the point where your plant wilts. You can remove the top inch or so of gnat-infested soil, place it in a bag, and dispose of it, or you could completely repot your plant. If you are going to reuse your pot, sanitize it before replacing it with a new potting medium. A systemic insecticide with imidacloprid will also kill fungus gnat larvae when applied to the potting soil.

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You may get your garden questions answered by calling the new Master Gardener Help Line at 218-824-1068 and leaving a message. A master gardener will return your call. Or, emailing me at and I will answer you in the column if space allows.
University of Minnesota Extension Master Gardeners are trained and certified volunteers for the University of Minnesota Extension. Information given in this column is based on university research.