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Fielding Questions: What causes cucumber fruits to curl?

Don Kinzler, gardening columnist 1 / 2
Curling cucumber fruits are most commonly caused by pollination problems. Special to The Forum2 / 2

Q: Why do my cucumber fruits always curl? Even small picklers curl. We had the soil tested at North Dakota State University and they said it was fine, and not to add anything. Any ideas?—Gary Lentz, Moorhead.

A: Curling cucumber fruits are most commonly caused by pollination problems. Cucumber flowers are pollinated by insects, mostly bees, that must visit each flower multiple times for complete pollination to produce a normal fruit. Inadequate pollination happens when there are too few bees, or when weather conditions are too wet, dry, hot, cool or cloudy.

If only part of a flower's ovaries is fully pollinated, the enlarging ovary, which is the little cucumber fruit, becomes lop-sided. One side lengthens, while the other side stays shorter, causing curved fruit.

We can't control adverse weather, but we can encourage bees to visit our yards by planting marigold, snapdragon, dianthus, poppy, clematis, monarda, borage, echinacea and many more types of flowers.

Because fluctuating moisture can also adversely affect fruit formation, try mulching cucumbers to keep soil uniformly moist. Wait to apply straw, dried grass or compost until soil has warmed in late June. Mulching too early keeps soil cool, which is the opposite of warm season crop requirements.

Q: I purchased several Dakota Pinnacle birch trees this past summer and rabbits have chewed off parts of the lower branches. One reason for planting these trees was to provide foliage from the ground up. Branches that weren't totally removed by the rabbits are four to eight inches long. Should I prune each branch back to the trunk, prune them all to the same length or just leave them?—Jim Kappel, Fargo.

A: Dakota Pinnacle birch can provide low-branched screening, but it's disappointing when rabbits destroy the lower branches.

It might be best to leave the remaining short twigs on the birch trunks. If rabbits don't do further damage, the shortened twigs could regrow in length this summer. Then you could decide if they should be pruned to the same length. If they are pruned back flush with the trunk, you might not regain the lower screening you want.

A wait-and-see approach might be best, and then decide what to prune after they've leafed out. That's actually the preferred time to prune birch and maple to minimize sap bleeding of these two tree types.

Q: I'm starting plants indoors from seed. Which types require deep seed starting mix to give their roots enough room to grow before transplanting?—Bob Schneider, Sioux Falls, S.D.

A: Plant types that need deep seed starting mix are also the types of plants that don't transplant well as seedlings because they tend to resent having their root systems disrupted. These types are best seeded directly into individual peat pots or Jiffy 7 peat pellets, so the entire unit, roots and all, can be transplanted into garden, instead of starting in a seed tray and transplanting little seedlings into cell-packs or pots.

Types that prefer deep mix and are best seeded into peat pots include watermelon, squash, cucumbers, muskmelon, pumpkin, and flowers like four o'clock, nasturtium and sweet peas.

Most other flowers and vegetables, even though they might have vigorous root systems, transplant well as little seedlings out of the seed tray and into packs and pots. The roots can be teased apart with little setback. Trays that are about two inches deep are sufficient for most seed types. It's best to fill the seed tray nearly to the top with seeding mix to increase air flow across the surface after seedlings emerge, which in turn helps reduce seedling damping off disease.

If you have a gardening or lawn care question, email Don Kinzler at All questions will be answered, and those with broad appeal may be published, so please include your name, city and state for appropriate advice.