CORVALLIS, Ore. – Salt can build up on both indoor and outdoor container plants. Whitish deposits, composed of salts from hard water and fertilizer, usually indicate insufficient drainage or not enough flow-through of water.
To avoid salt buildup, Ross Penhallegon, horticulturist with the Oregon State University Extension Service, recommends that every time you water plants in containers, let all the liquid run out of drainage holes at the bottom of the pot. To keep soil from washing out, place gravel or a broken piece of pottery over the holes in the bottom of the pots.
If you own a pot that doesn't have drainage holes and prefer to use it to grow plants, transplant your plant into a pot with drainage holes and then place it in the pot you prefer. Check the water level in the larger container by digging in the soil to avoid soils that are too wet.
Remove salts and hard water deposits from the potted soil once a month by flushing the potted plant with lots of water, about a gallon for a one-quart plant.
Keep the water in the bottom of pots or terrariums to a minimum. Root injury will occur if a plant's root system is submerged in water for very long. Excess water should be poured out of the larger container periodically to avoid creating habitat for mosquitoes to breed.
Another way to make sure potted plants get adequate drainage is to line the bottom of the pot with charcoal. Then cover it with a layer of coarse gravel. Next, add potting soil and place the plant. The water will drain through the soil to the gravel and the charcoal layers.
Always make sure there are holes in the bottom of all pots. Do not put compost in the bottom of pots. Compost will clog the holes and cause root rot. The charcoal will assist in neutralizing or absorbing noxious gases and other materials from the water.