No plant can survive without water, yet more plants probably die from overwatering than from under watering. Getting a grip on this simple procedure is one of the essentials of good plant care in the home. There are no fixed ‘rules’ about watering. How much a plant needs, and how often, depends not only on the plant but also the kind of pot (clay pots need watering more often than plastic ones), the compost (potting soil), (peat-based composts retain more water than loam-based), and the temperature and humidity of the environment.
When you water, fill the pot to the brim, dribbles are not sufficient. If the root ball has completely dried out, water may run straight through, down the inside of the pot, in which case stand the pot in a bucket of water until the air bubbles stop rising. After watering, always check whether surplus water is sitting in the saucer or cache-pot. This will not matter if there are pebbles or marbles to keep the bottom of the pot out of contact with the moisture, but otherwise you must tip out the extra water. Failure to tip outstanding water is the most common cause of problems. With just a few exceptions, if you leave most ordinary houseplants standing in water for a long period, they will probably die.
For easy and convenient watering, choose a watering can that is well balanced to hold and has a long, narrow spout that makes it easy to direct the water to the compost (potting soil) rather than over the plant.
Examine the pots daily if possible; appearance alone can be a guide. Loam based composts look paler when dry than when moist. A dry surface does not mean that the compost is dry lower down, but, if it looks damp, you will know that you do not need to water. The touch test is useful for peat based compost. Press a finger into the surface; you will know immediately if it feels very dry or very wet. The bell test is useful for clay pots. Push a cotton reel on to a garden cane and tap the pot: a dull thud indicates moist compost; a clear ring suggests dry compost.
Tap water is far from ideal for watering, but most houseplants will tolerate it. If the water is hard (has a high calcium or magnesium content), however, you need to make special arrangements for plants that react badly to alkaline soil or compost. These include aphelandras, azaleas, hydrangeas, orchids, rhododendrons and saint paulias. Rain water is usually recommended for these plants, but a good supply is not always available. If your tap water is only slightly hard, simply filling the watering cans and allowing the water to stand overnight may be sufficient. For harder water, try boiling it; part of the hardness will be deposited in the form of scale, and you can use the water once it has cooled.
Just a few plants tolerate standing with their roots in water, like this cyperus. With these you can add water to the saucer or outer container, but never do this unless you know the plant grows naturally in marshy places.
- Porous wicks are sold for insertion into the base of a plant pot, which is then stood above a reservoir of water. You can make your own porous wicks by cutting a piece of capillary matting (available at all good garden centers) into strips, as shown above. Make sure that the wicks and compost (potting soil) are moist before you go on holiday, and that the wick is pushed well into the compost.
- If it is summer, stand as many plants as possible outdoors. Choose a shady, sheltered position, and plunge the pots up to their rims in the soil. Apply a thick mulch of chipped hark or peat over the pots to keep them cool and to conserve moisture. Provided that you water them well before you leave, most plants will survive a week like this.
- Move plants that are too delicate to go outdoors into a few large groups in a cool position out of direct sunlight.
Watering correctly is an acquired skill, but, with practice, you will come to learn exactly how much or how little water your plants need. If you do find watering difficult or time consuming, however, other alternatives would be to use self watering containers, or to try the technique of hydroculture (also known as hydroponics) which will enable you to grow plants successfully with the minimum of attention. Hydroculture is a method of growing plants without soil or compost (potting soil). Watering is normally only necessary every fortnight, and feeding is only a twice yearly task.
You can buy plants that are already growing hydroponically, but, once you realize how easy hydroculture plants are to look after, you will probably want to start off your own plants from scratch. Not all plants respond well to hydroculture, so you may need to experiment, but the range of suitable plants is surprisingly wide, and includes amaryllis, aspidistra, some begonias, ficus, saint paulia and yucca, as well as cacti and succulents.
Routine care is very simple, wait until the water indicator (see step 3) registers minimum, but do not water immediately, allow an interval of two or three days before filling again. Always use tap water because the special ion-exchange fertilizer used for hydroculture (available from garden centres) depends on the chemicals in tap water to function effectively. The water must be at room temperature. As there is no compost (potting soil), cold water has an immediate chilling effect on the plant, a common cause of failure with hydroculture. Make a note of when you replace the fertilizer, and renew it every six months. Some systems use the fertilizer in a ‘battery’ fitted within the special hydroculture pot, but otherwise you can just sprinkle it on to be washed in with a little water.
- Choose a young plant and wash the roots free of all traces of compost (potting soil).Place the plant in a suitable sized container with slatted or mesh sides.
- Pack expanded clay granules around the roots, being careful to damage the roots as little as possible.
- Insert the inner pot into a larger, watertight container, first placing a layer of clay granules on the base to raise the inner pot to a level of about 12 mm/1/2 in below the rim. Insert a water level tube (available from garden centers). If you cannot find one specially designed to indicate the actual water level, use one that indicates how moist the roots are.
- Pack with more clay granules to secure the inner pot and water indicator. Sprinkle special hydroculture fertilizer (available from garden centers) over the granules.
- Wash the fertilizer down as you water to the maximum level on the indicator. If the indicator does not show an actual level, add a volume of water equal to one quarter of the capacity of the container and only water again when the indicator shows dry. A few months on and the house plant is flourishing.
If you find watering a chore, self-watering pots may be the answer. The moisture is drawn up into the compost (potting soil) through wicks from a reservoir below, and you will need to water much less frequently.