Fielding Questions: Growing sweet peas, holiday cactus dropping stem pads and more

Sweet peas. Wikimedia Commons / Special to The Forum

Q: I’ve tried growing sweet pea flowers, but by the middle of summer the vines turn brown and begin to die before many flowers are produced. Do you have any idea what’s wrong? I love the fragrance of sweet peas, and I’m disappointed I can’t get them to grow. — Amy B., Jamestown, N.D.

A: Sweet peas bring back wonderful memories, as my mother always planted them along the wire fence that surrounded our garden, and that’s where I first learned her recipe for success. A recent article by Cornell University reaffirms her old-time sweet pea wisdom.

Sweet peas thrive in cool temperatures, especially cool soil, so they’re best planted as early as possible, which in our Upper Midwest region is about mid-to-late April. Sweet pea plants are frost-tolerant down to 25 degrees.

Because the seed coat is hard, soak seed 24 hours in cold water. At the base of a fence or trellis, dig a furrow 4 inches deep, space seeds 2 inches apart and cover with 1 inch of soil. As the plants grow, gradually fill in the trench, which keeps the root system deeper and cooler.

When plants are 6 inches tall, pinch out the tips to produce multiple branching. While soil is still cool, add 4 inches of mulch over the root system. Sweet pea vines are susceptible to powdery mildew, so a preventative spray of garden fungicide is advisable as vines grow.

Q: Any idea why my holiday cactus is dropping some ends? The plant is about 4 years old. — Donna Braton, Barnesville, Minn.

A: It’s not always easy to tell why a Christmas or Thanksgiving cactus drops stem pads, because opposite conditions can cause the same symptom, such as warm drafts, cold drafts, or soil that's too wet or moist.

Holiday cactus, which are tropical cactus, require more water than desert types. Too much water, though, can cause root rot, which is a common cause of stem pads dropping. Underwatering can do likewise, although that’s less common. A 4-year-old holiday cactus is fairly manageable, so you might lift the cactus from its pot to be sure the roots appear healthy, and not blackened from root rot.

As a rule of thumb, holiday cactus should be watered when the top inch of soil is dry. Soil shouldn’t become bone dry, but never allowed to remain soggy.

Even if watering is done properly, the soil is sometimes the culprit. Poorly drained soil that is too dense or compacted can be starving the roots of oxygen. Holiday cactus appreciate a potting soil rich in organic matter.

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Q: How should I repot a schefflera plant that has been in the same pot for 30 years. I have cut it down, but now I think it needs repotting. — Gayle Pfau, Fargo.

A: Some houseplants are best repotted every few years, while others seem to enjoy going decades between, making it difficult to give a hard and fast rule for repotting frequency. But eventually something needs to be done for continued plant health.

Some old plants that would be too difficult to transplant and are in a proper pot size can be “top-dressed” with fresh potting soil by scooping out an inch or two of soil and replacing it, being cautious not to overly disturb roots. Other old plants can be totally repotted, increasing pot size by 1 to 2 inches.

Root systems of plants that have been in the same pot for decades should be handled with care, as not all plants will tolerate having the roots cut or disrupted.

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