Home Page

Plant Doctor Archive

Ailing indoor plants — 1

My indoor plants are not looking too healthy. Can you give me some general tips on how to look after them and how to get rid of bugs?


Indoor plants have tough lives. Most come originally from lush jungles or rainforests where they´re used to plenty of humidity and regular washing by rain showers. Contrast this with what the poor things will encounter inside the average house. Here it´s relatively dark and dusty, and often the plants are subjected to the unreliable care given by indifferent or very inexperienced plant owners. It´s no wonder so many indoor plants languish and die.

Here are some commonsense rules for revitalising your indoor plants:

New potting mix

The first thing to do is to check the potting mix. If a plant has been in the same mix for more than two years, it´s probably time the mix was freshened up. Either take the plant out and repot it into fresh mix in the same pot, or pot on to a slightly larger size. Choose a good quality potting mix; Yates Macroblend is a top quality multi-purpose mix for indoors or out.

Get rid of pests and diseases

Lots of pests and diseases just love indoor conditions. Keep a careful watch on houseplants so that insects and diseases don´t get the chance to cause too many problems.

Mealy bugs are sucking insects that develop a white, fluffy coating. They´re most often found in the crevices where leaves join the main stem, but they can also take shelter on the root systems of plants. Scales look a bit like plastic eggs stuck on the leaves, main veins and leaf stems. Each 'egg' disguises a sap-sucking pest. Both scales and mealy bug can be controlled with low-toxic Confidor available in a convenient to use aerosol.

Fungus gnats are tiny little flies that emerge from the potting mix and fly around the room. Although the flies don´t damage plants, they are annoying and their larvae can feed on roots and soft plant material. One simple way to get rid of fungus gnats is to reduce watering — fungus gnats flourish in moist conditions — and let the potting mix dry out between waterings. If the problem persists, take the plant outside into the shade and water through the mix with a pyrethrum solution.

The two most common indoor plant diseases are grey mould and powdery mildew. Grey mould affects flowers and soft growth, especially on plants with hairy leaves and stems. The plant material begins to rot and sprouts soft 'whiskers' before totally collapsing. There´s no effective cure, but the problem can usually be brought under control by picking off the damaged material and avoiding watering over the leaves. Powdery mildew looks just the way it sounds — patches of white powdery spores appear on the affected leaves. Begonias are particularly susceptible to this problem. Baycor, which comes in a convenient spray-can, gives excellent control of powdery mildew.

Watering wisdom

It´s often said that more indoor plants die from overwatering than the reverse. This is probably true, because the potting mix in indoor plants takes far longer to dry out than it would out of doors. Water plants well when the top surface dries, and make sure that water doesn´t sit in a saucer at the bottom. Permanently wet feet very quickly lead to rotted roots, followed soon afterwards by death!


Indoor plants don´t need very much fertiliser, so use a specially formulated indoor plant food such as Nutricote Indoor and Patio or use a half strength solution of your favourite soluble fertiliser.

UnitecAdvice by Dr Dan Blanchon from Unitec's Diploma in Sustainable Horticulture and Bachelor of Resource Management.

Reproduced with permission from NZOOM Home and Garden content,
from the previous website of  TVNZ News

The views expressed here are not necessarily those of the RNZIH

Home | Journal | Newsletter | Conferences
Awards | Join RNZIH | RNZIH Directory | Links

© 2000–2022 Royal New Zealand Institute of Horticulture
Last updated: August 9, 2005