How to Water Plants Correctly

3 June 2011, written by Bob Flowerdew

Plants are nearly all water, even wood is mostly water, with some carbon dioxide and a tiny amount of minerals. Water’s the pump that lifts sap with leaves evaporating it away so that more is drawn in by the roots. And water is the medium in which all internal processes take place. Thus providing ample water is a gardening priority.

Most temperate plants and especially garden crops grow most rapidly from spring thro’ summer and need about an inch of rain or its equivalent each and every week. Except in very rainy weather you can hardly over-water any plant growing in the ground. For almost all plants, especially vegetables, doing more watering will always give much better results; more flowers, lusher foliage, larger and sweeter crops. I find sweet corn, peas and beans, tomatoes and potatoes need most water from when their flowers appear and giving them even more from then on increases their yields tremendously. Others such as lettuces and most leafy salads really need continuously moist soil or they may become tough and bitter. So I now water much more than I used to and do so more often.

However few plants like water-logging and so we need to be much more careful with any growing in pots or containers. It’s easy to kill plants by standing their roots in wet compost or soil when they are not growing strongly as they drown. Roots need to take in oxygen and give off carbon dioxide and if standing in water they die rapidly. Unfortunately the plants then wilt and look as if they are short of water (which indeed the top growth really is), often resulting in even more watering and drowned roots becoming rotted beyond recovery. (Hydroponic culture has to make provision for root aeration, except for those water and bog plants which are especially adapted to such conditions.)

Different Watering for Different Plants

Roots in the ground can only be watered from above unless special irrigation pipes or funnels, tubes or similar are fitted which is well worthwhile. Usually most plants in the garden will have water supplied from a hose or pipe - don’t use a sprinkler if you can apply water to the soil directly not the plants. It’s better not to wet most plants as this can cause problems such as fungal diseases -and much will just evaporate away anyway. Water gently, with a rose (like a shower head) which will damage the soil less than a jet of water and prevent much mud splashing up onto the leaves. Also it’s better to wet the ground really heavily occasionally rather than to just splash a little about more often which can make the soil look damp on top while remaining dry underneath.

In pots though we have to be more careful - here roots are totally reliant on our watering and cannot seek out more on their own. We must water methodically and regularly. And we have a choice - whereas larger pots and containers with established plants can usually be watered from above with a rose on a can or pipe it is much better when sowing, pricking out and potting up small plants to water from underneath. I stand pots in saucers and fill, and then re-fill them as it’s sucked away. It’s important not to let pots stand in water for longer than a half hour or so before emptying any left in them or it could damage the roots. However this soaking upwards of water stops the top of the compost packing down so improving seedling emergence, and it prevents the other common problem of a wet surface remaining dry underneath. (If the compost ever gets totally dried out then submerge the pot for ten minutes in a deep bowl of warm ever so slightly soapy water, then drain thoroughly.)

As to the water itself, I use only (and preferably warm) tap water for sowing, small seedlings and delicate plants as many rots and wilts are caused by water from dirty rain barrels. We all must use only fresh clean tap water on salads and other crops eaten raw- for obvious reasons (see our article on Grey Water for details). Tap water is convenient and may be your only source of any quantity and will do for most plants. But in areas with hard water tap water will not suit acid lovers such as azaleas, blueberries and heathers. Rain water, held in clean rain barrels, is by far the best for almost all plants in the ground and even the more-so for those in pots as it has no chlorine or dissolved minerals which may build up in a pots’ compost. And when your plants are desperate even the dirtiest water from rain barrel, pond or ditch, and the grey water from your sink, shower or bath will have to do. But please do not use these on those salads….

By Bob Flowerdew.