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Fielding Questions: Sweet potato vine ailing, apples still clinging, tomato days to ripen

Gardening columnist Don Kinzler explains why a potted sweet potato plant is struggling, why some apples are still on trees and how to choose tomato seeds.

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This week, gardening columnist Don Kinzler helps a reader with a struggling sweet potato plant.
Contributed / Fielding Questions reader
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Q: What’s happening to this sweet potato vine? One of our sweet potato tubers developed a bud and I planted it. Any ideas to help the plant?

A: Congratulations on starting a sweet potato vine! Over the years I’ve noticed a common denominator in potted plants that are ailing, and I see the same situation with this plant, although I rarely see this discussed. I’ve noticed a direct correlation between plant problems and a too-deep headspace, which is the distance between the pot’s rim and the soil surface.

If the headspace is an optimum one-half inch, the soil profile is higher, creating a stronger gravitational pull when water is added, creating better drainage and soil aeration. A too-deep headspace favors soggy soil, less efficient drainage pull, insect and disease problems, and the tendency to build up salt and chemicals in the soil.

To start the sweet potato on its road to recovery, remove the plant from its pot, wash the leaves well to remove any lurking mites or insects, and then repot the plant into fresh, high-quality potting mix such as Miracle Gro potting mix or a mix recommended by a local garden center. When repotting, situate the plant so the finished product has only a one-half inch headspace.

Sweet potato plants will grow best if they think they’re in summertime Georgia. Give it as much direct window sunshine as you can in a warm, humid location. Fertilize every two-to-four weeks with an all-purpose houseplant-type fertilizer.

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Q: I have a number of apples still hanging from my Haralred apple trees. One tree has about 30 apples, and the other six. Is this unusual? – George B.

A: Apples still hanging on a tree in mid-January is unusual, and I’d enjoy a photo! Although it’s rare, it does happen. Let’s examine why.

As apple fruits ripen, a layer of cells forms at the point where the apple’s stem is attached to the twig or branch. The layer of cells is called the abscission layer, and when the layer is complete, it creates a breakaway point for the apple stem, and the fruit drops to the ground.

Abscission layers are triggered in part by the cultivar of apple, as some types ripen and drop in August, while others ripen in October, with abscission layers forming late. Besides apple type, abscission layers can be triggered by shortening days of fall and cooler temperatures.

When apples cling to the tree beyond what’s normal, a factor of some kind has interfered with the formation of the abscission breakaway layer. It might be an interaction of fall temperatures, or possibly dry soil conditions. It’s difficult to know the exact cause with certainty.

There’s a term for leaves or fruits that cling to trees well into winter, long beyond they’re normal drop date. They’re termed marcescent.

Q: I’m shopping seed catalogs for tomatoes and I’m looking for good main-season kinds. The days to ripening are listed, but how do you know which ones will be good for a main crop without being so late? – Stephanie D.

A: When looking for seed or shopping for tomato plants that are main season cultivars, I look for days to maturity listed at about 65 to 75 days. In our own garden, we want most of our tomatoes to fall into that category; most have good-sized fruits and ripen well during our main growing season.

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In addition, we enjoy planting some early cultivars, which are listed between 45 to 60 days maturity, and also some huge-fruited late types, which mature in about 80 to 100 days. Days to maturity are ball-park averages from the date of transplanting starter plants into the garden, not the date at which seed is sown.

Actual maturity date depends greatly on growing season condition, especially warm temperatures. But listing days to maturity allows us to classify tomatoes as early, main season or late.

If you have a gardening or lawn care question, email Don Kinzler, NDSU Extension-Cass County, at donald.kinzler@ndsu.edu . Questions with broad appeal may be published, so please include your name, city and state for appropriate advice.

More gardening columns from Don Kinzler

Don Kinzler, a lifelong gardener, is the horticulturist with North Dakota State University Extension for Cass County. Readers can reach him at donald.kinzler@ndsu.edu.
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