Vichai Atichartakarn, MD, wrote to say that many of his potted plants have leaves with brown edges. The leaves then die. “What is the cause?” he asked. “Is it because of lack of certain nutrient(s), too much sunlight, insects or disease? How can we correct and prevent it?”
Dead around the edges: These plants have been stressed by long periods indoors and a lack of water.
He added that some were previously used as houseplants but were moved to a shady place outdoors after he noticed the discoloration on the edges of the leaves. However, despite the move, the plants did not recover and instead more leaves had turned brown. “Could it be that the plants were already sick when they were moved outside? How best to rehabilitate them, any special nutrient?” he asked.
To give me an idea of what the plants were like, Dr Vichai sent me the photos that you see on this page. The three plants in pots and two planted in the ground all have leaves with burned edges. From just looking at the pictures it is easy to see the reason why: Despite regular watering they are not getting enough water.
In the pictures the ground is wet but the soil is compacted so the water could not penetrate it. Dig some 10cm to 20cm into the ground and you will find that the soil is dry; therefore the plants’ roots are not getting enough moisture. I suspect that the plants in the pots were allowed indoors longer than they should, which is probably why they are stressed. Either that, or the plants may be root bound, that is, there are more roots than soil inside the pot. It’s the soil which retains the moisture that sustains the plants.
Luckily, all the plants — two varieties of aglaonema, a dieffenbachia, a homalomena and a maranta — are of the sturdy type and can be rescued, but it needs some work.
For the plants in the ground, I suggest that the hardened soil be augmented with equal amounts of finely chopped coconut husk and/or rice husk and compost or leaf mould, to make the soil porous. You may have to dig out the plants first so you can mix the planting material thoroughly. Before replanting them in the new medium, trim off the dead leaves or some of the leaves with severely burned edges. Add a handful of fully decomposed animal manure to the planting medium, mix thoroughly then put the plant in the hole, fill the hole with the soil mixture and water thoroughly.
Remove the potted plants from their containers and trim off some of the roots before repotting them in containers one size bigger than the old ones, using the same planting mixture as above. Some gardeners topdress the soil with animal manure instead of mixing it in. For the squeamish, organic fertiliser is available in pellet form; add just two to three spoonfuls per plant if you are using this. One week after replanting, apply a pinch of complete fertiliser (NPK 15-15-15 or equivalent) every two weeks as supplement. However, if you are using a slow-release fertiliser you don’t have to apply again for three months.
In need of a drink: These homalomena and Maranta plants are dehydrated. Overly compacted soil prevents water from really penetrating the ground, so plant roots do not get enough moisture despite regular watering.
The forebears of many of the plants we grow today were collected from tropical jungles, where they often thrived in the shade of trees and vines. In an environment where many species compete with one another for exposure to the sun, plants develop thick green leaves, which combine that green substance, called chlorophyll, with carbon dioxide absorbed from the air and energy from the sun to manufacture food through the process of photosynthesis. These foliage plants, or hybrids with these plants as parents, are more tolerant to indoor conditions than flowering plants such as gardenia or roses.
Plants require four essentials to thrive — water, light, the right temperature and nutrients. Unlike in cold countries, plants cannot remain indoors in Thailand for months on end as most Thai homes or buildings cannot provide enough of these essentials. The soil may be moist and rich in nutrients, but if the light is inadequate, or if humidity is lacking, plants begin to deteriorate after a week or two.
When buying plants for your living room, choose those that are in top condition and, if possible, have been grown in a nursery with a low-light environment. Whether they are outdoors or indoors, different plants require different levels of light. If you see that despite being given tender loving care, a houseplant’s leaves turn yellow, it may be getting too little light so try shifting it to a brighter location.
Water your houseplants when the soil is dry to the touch. One golden rule is: “Be thorough when you water and don’t water again until the soil is dry.” A little watering induces the plant to keep roots only in the moist surface of the soil, which means that it will wilt immediately if ever you neglect to water it.
Thorough watering of pot plants can be done by immersing the pot (but not the whole plant) in a basin of water until it stops bubbling. This ensures that the soil has been moistened all the way to the bottom of the pot. Doing this once or twice a week is more effective than watering the plant a little every day.
Make sure that the pot has stopped dripping before you put it back to its stand, to avoid water-logging. Water-logging, or saturating the soil with water, is as detrimental to plants as letting them go bone-dry; a friend of mine lost a prized plant when excessive watering caused it to stand in a saucer filled with water for several days.
In order not to stress your plants, leave them indoors for 10 to 14 days at a time then move them outdoors to recuperate. Make sure that the place where you move them has filtered light, as putting them in direct sun can burn their leaves.
To help the plants recover, trim and remove dead foliage, give them enough water and feed them with fertiliser. Wait three to four weeks or until they look like they are back in top form before moving them back inside.
Having plants that you can move indoors while others are recuperating will ensure that there is always greenery inside your house or apartment, office or even clinic, if you have one like Dr Vichai. n
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