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Fielding Questions: Tips for houseplants with brown leaf tips, redbud trees and lights for seedlings

A reader ask Don Kinzler why the leaf tips of several houseplants have started to turn brown. Special to The Forum1 / 2
Don Kinzler, Growing Together and Fielding Questions columnist. The Forum2 / 2

Q: Do you know what is causing the leaf tips to dry out and turn brown on several of our houseplants, and do you have any suggestions how to solve the problem? We water with Fargo tap water, and don’t have a water softener. — Gary Leeby, Fargo.

A: Browning of leaf tips is a common houseplant disorder with several causes. Low indoor humidity and hot air drafts contribute to the problem, but by far the leading cause is the buildup of salts and minerals in the soil.

Although too-frequent fertilizing can be a cause, the most common culprit is the accumulation over time of minerals in the soil from normal watering. We should never let plants sit in drainage water, which can be heavy in leached salts. To flush the soil several times a year, set the plant in a sink or tub and drench the soil three times in quick succession until water flows generously out the drainage holes, which leaches minerals from the plant’s soil.

Repotting into fresh potting mix every several years is another remedy. I notice from your photos the plants might be in the original black nursery-type pots, so I think repotting into slightly larger pots and fresh soil would be wise.

Unfortunately, leaf tips that are already crisp-brown will never revert to normal, so improvement in plant appearance depends on formation of new healthy leaves. Trimming away brown leaf tips into natural points helps somewhat while waiting for new leaves.

Q: I saw a tree in a seed catalog called eastern redbud. It shows zones 4-7. Do you know if others in our area have tried them? — Kay Hogetvedt, Felton, Minn.

A: Eastern redbud, Cercis canadensis, is a pretty, rosy-red, spring-flowering small ornamental tree. Although its winter hardiness is listed as zones 4 to 7, zone 4 covers a large north-to-south chunk of the Upper Midwest, and Eastern redbud is considered non-hardy for most of North Dakota and the upper two-thirds of Minnesota.

Good news! A new redbud, named Northern Herald, has been introduced by North Dakota State University with increased winter hardiness. Listed as zone 3b, it has flowered consistently in North Dakota test sites. Like many new tree introductions, it will take time before Northern Herald is available at local nurseries, but we can be on the lookout.

Q: I’m planning to start seedlings under fluorescent lights. Out of curiosity, what happens if you leave the lights on continually 24 hours a day? Will they grow more quickly? P. Henson, Bismarck, N.D.

A: In my own experience, most seedlings and plants grow fine under continuous lighting. It’s debatable, though, whether continuous lighting makes them grow any faster than 16 hours of light followed by eight hours of darkness, which is a standard rotation for growing seedlings indoors.

In scouting for research reports, I couldn’t find conclusive results showing whether continuous lighting resulted in improved plant growth across the board. Over the years, I’ve opted to set our timer for 16 hours of light for the seedlings we grow. Some plant species seem to require a period of darkness each night for best growth.

Because there are thousands of horticultural plants, it’s difficult to scientifically test them all for their reaction to light duration.

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.