Dr. Leonard Perry, Horticulture Professor
University of Vermont
Houseplants drop leaves for many reasons, but most are related to improper care or poor growing conditions. Often just giving plants the correct light and temperature, or controlling pests, is all that is needed to prevent future leaf drop.
Either too much or too little watering may cause leaf drop. A common problem is that when you see leaves droop or even fall off, you may be tempted to think the plant is thirsty and needs more water. This could lead to overwatering and even more leaves dropping. Make sure when watering, especially in northern climates in winter, to use lukewarm water. Icy cold water can chill the soil and injure roots of tropical plants, leading to root rots, leaves dropping, and perhaps even dead plants.
Extremely low humidity will cause sensitive plants, such as gardenia, to drop leaves although most common houseplants will not show leaf drop in response to low humidity only.
Fertility, or rather lack of sufficient nutrients, can lead to leaf drop. With this, usually you will notice leaves lighter in color first, so you have a chance to correct this before leaves totally turn yellow and drop. Use a houseplant fertilizer, according to label directions, particularly while plants are growing or flowering.
Plants in pots that are too small may drop leaves. Why? Because there may not be enough root room to support all the leaves the plant tries to form, so the oldest leaves drop off. Because the space for the roots is inadequate, the plant may not be able to absorb enough water and nutrients.
Some leaf drop occurs when plants are subjected to a big change in environment. Such changes occur when plants grown outside for the summer are brought inside for the winter. Greenhouse-grown plants may drop leaves if placed in dimly lit house conditions, when they’ve been grown in high light. Some plants just may require higher light to grow and keep all their leaves. Leaf drop brought on by a change in environment should be temporary and non-life threatening (to the plants), new leaves forming that are adapted to the new site.
Chilling is one cause of leaf drop related to environment. Tropical plants are sensitive to low, but above freezing, temperatures. Plants on windowsills may be exposed to chilling temperatures. Hot or cold drafts may be a problem for some plants. The poinsettia is a prime example of a plant that drops leaves due to exposure to cold drafts of air.
Insects and diseases can cause leaf drop, but are not as common as the previously listed causes. Recently I had a variegated English ivy that was losing leaves. On closer inspection I found leaves infested with spider mites. Washing plants well with mildly soapy water is a good start, and often all that is needed, for pest control.
Some leaf drop on houseplants is normal. Older plants should be expected to drop a leaf or two occasionally. This is particularly the case with plants that grow upright like umbrella plant or cane plant, losing lower leaves as newer ones form on the top. The only solutions for this are to stake plants and live with this habit, to propagate new plants by air layering the canes, or to give away the plant and get a new more compact one.
If you’re not sure of the correct culture and conditions for your houseplants, check any directions that came with them, look online or in books, or ask your local full-service garden center.
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