I do not seem to have a good handle on watering my indoor plants. I water all of them about once a week. Some pots have mold growing on top of the soil. Other plants are developing yellow leaves. Could you give me some pointers on proper watering?

Mold growing on top of the soil is usually an indication of too frequent watering. Yellow leaves can also be caused by over watering. However, inadequate fertilization is another possible cause.

Many factors affect the frequency of watering needed for specific plants. What are the light and temperature where the plant is growing? How big is the plant in relation to the pot? What type of soil is it planted in?

The best single way to determine if a plant needs water is to feel the top of the soil with your finger. If the soil is dry on top, then it is probably time to water. After you have watered a plant several times you will find out about how long it takes to dry out. Wet soil is darker than dry soil, so after a while you can tell by color when a particular soil is starting to dry out. Not all potting soils are the same color, so you need to feel the soil a few times until you learn the relative color.

Since there are so many factors involved in how often a plant dries out, you should not try to water all plants at equal intervals. If you check plants every day or two for awhile you will find out which ones need frequent or infrequent watering.

Plants with thick leaves such as cactus and Jade plant like drier soil than plants with thin leaves. Drooping or wilting of leaves is a sign that a plant is too dry.

Water quality is also important. Softened water has more sodium chloride than is good for plants. Sodium chloride or table salt damages plant roots and soil structure. Most cold water taps in the kitchen do not have softened water. However, cold water can slow plant growth, especially in the winter. I like to fill my watering can with cold water and let it sit until it reaches room temperature.

I would recommend scraping the mold off the top of the soil and replacing it with fresh potting soil. If you adjust your watering frequency so that the soil becomes dry on top, you should not have problems with the mold coming back.


Allen Wilson

Allen has been writing about gardening for over 30 years. He is a retired professor of Horticulture.

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