The Richmond Register

January 9, 2013

Houseplant Problems

That ‛crusty white stuff’ on plant leaves is soluble salts

By Amanda Sears
Extension Agent

RICHMOND — What is that white crusty stuff that appears on the soil and pots of houseplants?

The white or tan crust on the surface of house plant potting mix is a build up of soluble salts. Excess soluble salts burn foliage, damage roots and lead to problems with water uptake. Wilting, yellowing, and marginal and tip burn of leaves, also called scorching, are symptoms of excess soluble salts.

Soluble salts also accumulate on the outside of clay pots, around drainage holes on pots and even on the stems of plants. Salts come from the potting mix, fertilizers or high salts in the water used to irrigate the plants.

These salts rise to the surface of the potting mix by a process called capillary action, especially when the pot sits in a saucer containing excess drainage water. Excess salts cannot drain through the pot when saucers keep water under the container because the water is re-absorbed. Leaching salts from the soil is an easy remedy for plants affected by excess salt.

Why did my houseplants develop yellow leaves and leaf drop when I moved them to a new locations?

Abrupt change from a location in high light to one in low light may be damaging. Plants can become acclimated to one location. Leaves gradually face toward light for maximum light absorption. Moving the plant disrupts this orientation, and light is not used as efficiently for a period of time. This is especially true of large plants. Moving plants abruptly to more intense light also results in bleaching or burning of foliage, especially in direct sun. Any changes should be made gradually. Many plants can be kept from getting one-sided by turning them once a week.

When and how should I repot my houseplants?

Consider repotting houseplants in the spring when new growth starts. Turn each of your plants upside down, tap the edge of the pot and remove the plant. If the roots are in a solid mass, the plant needs to be repotted.

Shift the plant to a pot 1 or 2 inches larger in diameter (with a drainage hole). Add new soil to the container. For most plants, use a commercial peat-lite mix, or make your own by combining three parts sphagnum peat moss, one part vermiculite, and one part perlite or sterile sand.

Before setting the plant into the pot, gently loosen the root-ball so the roots will move out into the new soil. After adding the soil, water to eliminate any air pockets. Usually you will not need to water as frequently for a few months after repotting.

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