A common practice in spring is to take your houseplants outside and give them a good shower with the hose, allow them to dry and take them back in the house.
This sounds like it would be helpful for your plants, but it can easily damage them.
When a plant grows outside, it produces leaves called sun leaves. In a sun leaf the chloroplasts are stacked on top of each other. A chloroplast is a structure in a plant cell that contains a pigment called chlorophyll. The function of the chlorophyll is to collect sunlight and convert the sunlight into sugar.
In this arrangement the top chloroplasts are burned by the high light; however, the damaged chlorophyll shades the bottom chloroplasts. Because of the abundance of sunlight, the loss of a few chlorophyll does not affect the plant’s ability to produce energy.
A plant growing in the low light levels such as in a home will produce a leaf called a shade leaf. A shade leaf is thinner, and the chloroplasts are spaced evenly through the leaf to collect as much light as possible. If you move a shade plant or houseplant outside even for a short time, the leaves can be severely burned by the sunlight. It may take the plant a couple days for the leaves to turn yellow and fall off the plant.
Many people do not associate the leaves falling off with too much sun several days before. Many are more likely to think it was the water.
A similar problem will happen to a sun plant moved into a dark location; because of the arrangement of the chloroplasts, the plant will not be able to absorb enough light and the leaves will turn yellow and fall off. Our eyes adjust quickly to the light change, but the leaves cannot change the arrangement of the chloroplasts. This could take months for the plant to lose its leaves.
If you need to wash down your plants outside, make sure you place them in a full shade area and move them back into the house as quickly as possible. It may even be better to place them in your shower and use a hand-held shower nozzle to wash your plants and let them dry in the shower.
While your plants are in the shower for cleaning, it may be a good time to help your plant in another way.
If houseplants are allowed to dry out too much and the soil shrinks, away from the side of the container, this leaves a space that allows the water to run through the container without wetting the potting soil. If your potting soil has a lot of peat moss, it will shrink when dry and once it is dry it will be very hard to get the soil wet again.
To solve the problem, place the plant in the sink or bathtub and prevent the water from going down the drain. Fill the sink with water and allow the plant to soak in water for a few hours. This will force water into the peat moss and the soil should expand and fill in the container.
After soaking for a few hours, drain the sink. Leave the plant in the sink and water the plant a couple of times, allowing the water to drain out the bottom of the container. Fertilize your houseplant and place the houseplant back in its normal spot.