Garden Detective: Saving ailing palms and pruning corn plants

DEAR JESSICA: Enclosed is a photo of my sago palm, which I am struggling to keep alive, as it was my mother’s. As you can see, as new fronds begin, they begin to die at the ends and do not grow into anything. Once they die, new ones will appear. The only thing I can think of is that I moved it into a pot that was too large for it. It’s planted in Miracle-Gro moisture-control potting mix. Other than that it gets sun, and I water from the bottom every other week. Can you determine what may be causing this? — Nancy Perosio, Massapequa Park

DEAR NANCY: Your plant is pretty far gone, but I understand the sentimental value it must hold, so let's do our best to try to save it. It’s possible that the large pot, coupled with the moisture-control potting mix, is retaining too much water and beginning to rot the roots. This is easily confirmed by gently slipping the plant out of the container and inspecting its roots. If they are dark and/or mushy, they are rotting; if the rot is widespread, there isn't anything you can do to save it.

If only some of the roots appear rotted, however, there's hope. Trim away the rotted roots, then soak the remaining roots in a biological fungicide (diluted according to package directions) for 30 minutes, followed by another soak in diluted rooting hormone (again, following package directions). Repot the plant in straight perlite and resist the urge to fertilize, as that would force the ailing plant to divert its energy into growth instead of healing — further weakening the plant. After several weeks (perhaps a few months), when the plant regains vigor, repot it into a high-quality potting mix that contains sand or a similar ingredient to increase drainage; fertilize it using a high-quality, slow-release palm fertilizer once a month. Always allow the soil to dry out between waterings.

If the roots look fresh and healthy, my best guess is that your plant is deficient in manganese, a micronutrient necessary for healthy growth. Apply manganese sulfate (not to be confused with magnesium!), following package instructions. A plant the size of yours won't need more than an ounce, probably less. Water afterward, and going forward apply a fertilizer specifically made for palms (sago palms aren't true palms, but their requirements are the same).

Best of luck!

DEAR JESSICA: I’ve included a picture of an indoor palm tree that I bought many years ago at Fort Lauderdale airport; it’s the kind they sell to tourists to take back home. I put it outside during summer months, in a mostly shaded area, where it thrives. Would you be kind enough to render some advice as to why the tips of quite a few of the leaves look like they do? — Jim Novak, Massapequa

DEAR JIM: Thank you for answering my follow-up questions and sending more photos of the undersides of the leaves, where some insects typically hide.

The three usual suspects in such cases of decline are insufficient watering, improper sunlight exposure and insect pests. Because you’ve raised the plant successfully for many years, presumably in the same spot, we probably can rule out sunlight as a factor in its decline. And a close inspection of your photos did not reveal any insects. That leaves us with moisture.

The soil should be kept consistently moist, but never soggy. Being a tropical plant, your palm also requires humidity, so keep it away from radiators or heating vents, and consider running a humidifier in the room (otherwise, mist the plant daily).

Usually, I wouldn’t recommend fertilizing over the winter, but you can try giving the plant a single dose at half strength of a product that contains iron.

Trim away the brown leaf parts using sharp scissors, and ensure the plant continues to get bright, indirect sunlight exposure.

DEAR JESSICA: I am not sure what this plant is called but we call it a corn plant. It is almost reaching the ceiling, and I am not sure how to stop it from getting any taller. I was wondering if you could help me. Can it be trimmed at the top? — Elaine Winters, via email

DEAR ELAINE: Yes, you have a corn plant. And, yes, you can cut the top off to shorten it. The remaining stump almost always re-sprouts in a matter of months, but there is always a (very) small chance that it won't.

To cover yourself — or if you'd just like to create another plant for free — you can root the part you remove by dipping the cut end in rooting hormone and planting it in a container of potting mix, at the same depth as the original.