Q: I’ve had my first houseplants for a few months and they now look dusty. Do I need to clean them?
A: A clean houseplant is a healthy plant. Dust and dirt that collects on plant leaves filters the sun’s rays and interferes with respiration. A clean plant uses light to create its own food, using chlorophyll. Dirty leaves dramatically inhibit that process.
Ways to clean your plant
When plants are outdoors, their leaves get cleaned by the wind and rain, so you can mimic that by dusting the houseplants’ leaves or by giving them a rinse in your shower, or in the kitchen sink with a spray of water. The most ideal situation is to have your plants grouped in an area over a tile floor, and spray them with a bottle of purified water every other day. Palms and ferns flourish when they have water sprayed on their leaves.
You can dust leaves with a feather duster, or gently whipe each blade between two damp paper towels or clean soft cloths. Start cleaning at the base of the leaf, near the stalk, and draw gently outward, to the tip of the leaf.
Leaves with hairy surfaces are not good candidates for the wipe-off method, like African violets, or geraniums. It is best to keep water off their leaves as water spots may damage the leaf.
Look closely at your plant
While cleaning your plants’ leaves, it is a good time to remove damaged, dead or yellow leaves. You can trim just the edge of the leaf, but the edge will turn brown. Or you can cut off the whole, failing leaf near the stem.
This is the ideal time to take a close look at your plants. Why did those particular leaves die? If they are near the bottom of the plant, they could just be old. If a leaf in the middle has died, look more closely, near the stalk, for fine little webs, an indication of spider mites. If the newest leaves have died, it may have an insect problem, or the plant may be over watered.
Fungus gnats are common to houseplants that get extra water. These little fly-like creatures come from the outdoors, and are virtually harmless, if a bit annoying. The larvae may damage the root hairs of your houseplants. To control them, keep the soil a bit dry, or apply one of the treatments discussed in the fact sheet, below.
If all the leaves have yellowed, your houseplant may need more light, or more iron. There are many things that can affect your plant. For more information, refer to the CSU Cooperative Extension Home & Garden Fact Sheet no. 5.595 Managing Houseplant Pests by visiting the http://www.ext.colostate.edu website or contacting the Master Gardener Help Desk, 636-8921, Monday through Thursday.
The two main things that affect the health of your plant are the amount of light it gets and the amount of water it gets. CSU always emphasizes, “right plant, right place,” as with outdoor plants.
Touch the soil gently, and see if it is damp or dry. Only water plants with dry soil. If you plant is leaning toward the light, you can turn it a quarter turn, to encourage it to grow in a balanced fashion. You may have to move a plant to a sunnier or less sunny location during the year. For example, when the sun is low in the sky in the winter, much more sun comes in house windows. Conversely, when the sun is high in the sky in the summer, my plants get much less direct sunlight because the widow over hangs block the light.
How to repot a plant
Most house plants need to be repotted every three years or so. You may even see roots coming above the soil, looking for more dirt, as spider plants do. It is easy to do at home, and the plant will benefit from the renewed soil.
Lay out several layers of newspaper on the work surface. Lay your house plant gently on its side, loosening the sides, like you would a cake. Then, holding the top of the plant, tip the bottom up and shake it lose. There may not be much soil left, but it should smell nice. Notice if the bottom hole was plugged. Notice if a salty film has built up around the edge of the pot.
New pot or reuse the old pot
If reusing the original pot, scrub it in some warm water to clean it, and remove as much of the salt build-up as possible. The salts come from the additives in our tap water and from fertilizers.
When the plant is lying on the newspaper, you may see that there are several independent groups of plants. These may be separated and potted separately, creating new plants. African violets and spathe or “peace lilies” like to be divided frequently.
If all the roots are crammed into the pot, you may want to reduce the roots before placing it back in its original pot, or put it into a larger pot. With the gregarious spider plant, you can simply cut off a number of the external roots, and repot it in the same pot.
If you are working with a tree-like plant, like dracaena, you will want to find a pot just a bit larger than its current pot. Dracaena need good drainage, and easily develop root rot, so putting pebbles on the bottom of its new pot will increase drainage.
With the pot upright, and some pebbles in the bottom, add a little houseplant soil. Hold the plant over the bottom soil so its roots dangle freely, and fill in around the roots with the new soil. Gently press the plant into its new home, and top with a little extra soil.
The selection of potting soils is vast, so look for soil that is intended for indoor plants. Many potting soils contain fertilizers, so you will not have to fertilize for a while.
As with outdoor plants, repotting is a good time to trim a plant back. At this time, trim dead flowers, and cut a bit off the top of a plant encourages its roots to grow. Often, you can place that cutting in water and propagate new plants. Schefflera can multiply throughout your house, this way.
These are examples of vegetative propagation, ways that plants can multiply, without using seed. Vine plants are easy to propagate: you simply snip off the end, and put it in a glass of water. In a few weeks, you will see roots growing, and you can expand your indoor plant “family”.
Contributed by Brook E. Mark and Peg Zimprich, Colorado Master Gardeners. For answers to your horticultural questions, contact the Master Gardener Help Desk at 636.8921 or CSUmg2@elpasoco.com
(A version of this article appeared in The Gazette on 2/14/09.)