I have had a lot of questions on dead houseplants, my answer is you have over watered, under watered, too much light, not enough light, too cold, too warm, drafty conditions, too much fertilizer now, etc. Hopefully you do not think I am full of it! It all depends on what type of houseplant you have.
More houseplants die from over watering than from any other cause. Adjusting your watering routine once houseplants are move back inside the house is essential for the plant’s continued survival. Most plants benefit when the soil is allowed to dry slightly between watering. This dryness ensures that oxygen penetrates to the plant’s root system, oxygen that is just as essential for good plant growth as water. Often a plant can be allowed to wilt slightly before it is watered; thus, giving an indication when water is needed.
No matter if the plant is a cactus or an azalea that needs continual, even moisture, always water plants thoroughly. A thorough watering wets the entire soil ball in the container and leaches away excess fertilizer salts built up in the soil. Fertilizer salts can burn roots resulting in burnt or dried leaf edges and plants that wilt, even though they seem to have plenty of water. I water by placing the container in an empty sink, adding water until the water comes through the drainage hole.
A plant that needed watering once a day while outside in July and August may only require watering once a week in the house during winter. Test the soil moisture levels before watering. If the top one-inch of soil feels dry or the plant begins to wilt slightly, most plants will be ready for another watering.
Also keep in mind that some plants, like ferns, Rex begonias, Prayer Plant and Calathea to name a few, require high humidity to grow well so mist once or twice a day or group plants together. Indoor humidity levels are usually lower than those in a greenhouse, in fact during winter when furnaces are running, indoor air can be as dry as desert air.
Fertilizer, easy. Do not fertilize during the winter. Avoid over-fertilization, plants require less fertilizer under low light conditions and for houseplants, almost all indoor locations are “low light” when compared to outside light levels, especially during the winter. Burned or dried leaf margins and wilted plants can also be a sign of root damage to the plant caused by salt buildup in the soil from over fertilization.
One thing to remember for most cactus and many succulents are they thrive if kept cool during the winter months. Lower temperatures encourage the development of sturdy plants and stimulate flower bud development. Most cactus do best at temperatures from 45-55 degrees Fahrenheit, however, they still require high light conditions during this period, so a cool bedroom or porch with a south facing window would be ideal.