Showdown: Horse vs. cow manure in the garden

DEAR JESSICA: Is it OK to use horse manure instead of cow manure for fertilizing my vegetables and flowers?

— John Wolf,

Levittown

DEAR JOHN: Horse manure and cow manure are similar in nitrogen content when fresh, but when dried, or “aged,” horse manure is richer, so the first thing to consider when deciding between them is the needs of your garden and specific plants.

Horse manure also often contains seeds from the hay the horses consume, which could result in unwanted weeds. It’s important to use only manure that has been aged for several months (or hot composted), as fresh manure will burn plant material and contains pathogens that can infect and impair your plants. This should always be a consideration but is even more important when treating edibles.

If you will be purchasing manure, I would recommend choosing a cow product. But if you happen to have access to horse manure, it’s fine to use, as long as it’s been composted, which would reduce the viability of hay seeds as well as kill any harmful pathogens.

DEAR JESSICA: I am inexperienced in garden and plant maintenance. I purchased a potted hibiscus this fall and, as instructed, brought the plant indoors. Some leaves have turned yellow and have fallen. Would it be harmful to use the fallen leaves as a self-generating mulch and supplement for the plant?

— Daniel Hwang,

Huntington Station

DEAR DANIEL: It’s expected that potted hibiscus plants, brought indoors for the winter, will lose some or even most of their leaves — and even look sickly by springtime. But that’s OK: They’ll resume their vigor and growth when they are returned outdoors and fertilization resumes.

Using fallen leaves to mulch your potted hibiscus, however, isn’t advisable, as the plant isn’t exposed to the same conditions as garden plants are outdoors. In the garden, insects and worms work the soil and help break down organic matter, such as leaves, into a rich byproduct that nourishes soil, and by extension, plants. Left on the soil surface of a potted plant, the leaves will not likely have the same beneficial effect.

Place the plant near your sunniest window, clean up the fallen leaves and water lightly when the soil is dry. In May, prune back a bit, fertilize and begin reintroducing the plant outdoors for incrementally longer periods each day, over the course of a week, before leaving it outdoors for the duration of the season around Memorial Day.

DEAR JESSICA: I started growing my avocado tree from a pit almost two years ago. It’s been doing well until recently. In August, some of the leaves turned brown and crispy and were falling off by themselves. I thought it was from some sort of burn, so I gave the plant a thorough rinse and that seemed to help until about a month ago. The leaves are shriveling up and are crunchy to the touch, breaking apart easily. But this time they aren’t brown and falling off themselves. Here are some photos. I’m not sure what to do and would appreciate your help.

— Jessica Bologna,

Commack

DEAR JESSICA: Brown avocado leaves usually indicate a salt injury caused by over-fertilization — or a buildup of salts from fertilizer over time. The remedy for this is to flush out the salts, as you have done, by running water through the soil and out of the drainage holes at the bottom of plant pots, essentially rinsing away the excess mineral.

Because you are seeing similar symptoms now, either you have been fertilizing too much, and again need to flush, or you’re not watering enough, as curled leaves could indicate a lack of moisture.

Be sure to water thoroughly and properly — placing the pot in the sink or bathtub and slowly adding water until it drains from the bottom. If, instead, you were to merely add enough water to moisten the top of the soil, the roots would not benefit, and the plant would react by curling its leaves in an effort to retain water.