How much water does a house plant need? Most prefer a reliable source of moisture – neither too much, nor too little. In most cases, house plants will readily reveal their needs, which vary from plant to plant and season to season. If you learn to read the signs you’ll know whether you plant is thirsty once you’ve mastered watering, don’t be surprised when your house plants grow and bloom more vigorously.
When your house plant is too dry
Plants rely on their cells being full of water to provide support. When water is in short supply, their cells shrink and the plant begins to wilt. Most wilted plants recover once watered, but try not to let them wilt regularly. Instead, look for the early warning signs; feel the compost with your fingers and if it feels dry to the touch, then water. Dry compost looks pale and weighs less than when damp, so if in doubt, lift your plant to see if it’s heavy. When a plant is severely droughted, the compost may shrink away from the pot, so any water will run straight through. If this happens, stand the pot in a basin filled with water and leave it there until the compost has expanded.
When your house plant is too wet
The best way to know if you’re overwatering is to check the compost ? if it feels damp, don’t water. Overly wet compost can give off a stagnant smell while the upper layers may turn green. If you see clouds of small flies on the compost surface, it’s another sign that you’re being overly generous when watering. Plants that get too much water may drop their leaves, leaf tips may turn black (as in peace lilies) or plants may turn soft and rot (cacti, succulents, orchids). If you suspect you’ve been too generous, stop watering completely until the compost dries out. Badly affected plants may not survive so take cuttings from any healthy leaves or stems.
Seasonal differences with house plants
After a few weeks of regularly checking your house plant’s compost, you’ll begin to recognise when it’s thirsty and can water appropriately. But do keep checking it regularly, as your plant’s water needs change from season to season. Weekly watering in spring may increase to twice weekly in summer, when the weather is hot. Also, if your plant is kept outside during the warmer months, it may need water daily. During the cool days of autumn and winter, most plants don’t grow much so reduce watering and, as ever, feel the compost if in doubt.
House plants that require different watering
While these rules work for most regular house plants, there are a few groups that need special treatment. Carnivorous plants hail from bogs and marshes, so they need wet compost at all times. At the opposite end of the spectrum, desert cacti and succulents need much less water. In summer, water regularly, but in winter give only the bare minimum to succulents and keep cacti completely dry. Orchids can be challenging as their potting compost always looks dry, but don’t be tempted to water too often as their fleshy roots rot readily. With moth orchids (Phalaenopsis), wait until the roots look a silver colour before watering (the roots turn green when wet). With all others, water with caution, if the pot feels light when lifted.
Feature by Dr. Ross Bayton.