Over-Watering Pot Plants

Most people know plants should not be over-watered. That's the problem. Thinking that giving too much water at one time will kill the plant, they adopt a policy of 'little and often' just to be safe, usually in the form of a daily top-up.

Since more water is invariably given than can be utilized, the compost gradually becomes wetter and wetter, giving the plant a slow death by drowning. This wetting happens so gradually it is virtually imperceptible.

I want you to be quite clear about something:

Provided the plant is flowering in an appropriately-sized pot (i.e. pot is not too large and its roots occupy most of the compost), and provided there is an unblocked drainage hole(s) in the base of the pot (i.e. it can drain freely), it should be almost impossible to over-water, in the sense of giving TOO MUCH water at one time.


So WHAT EXACTLY IS OVER-WATERING?

Not all plants are sensitive to over-watering, since some are specially adapted to deal with it. However, others can be particularly sensitive.

If a plant's roots are left too long in soggy compost (or soil), short of oxygen, they are unable to breathe (respire) properly (aerobically) in the normal way. Consequently, a process called 'anaerobic respiration' occurs. Alcohol is produced which kills the white healthy roots and turns them brown. Unless detected early enough and dealt with by drying out the roots, death quickly follows.

So over-watering is caused by giving too much water over a period of time.


HOW IS OVER-WATERING DETECTED?

Wilting is a sure sign of water stress. However, it can mean different things:

• In a WET compost, wilting is a first sign of over-watering, since the suffocating roots cannot take in water.
• If wilting occurs in a DRY compost, the opposite is true: the plant NEEDS water.
• But if wilting occurs in a DAMP compost (usually in hot weather), this can be quite normal. All that has happened is that the roots cannot take in water fast enough. Once things cool down, normality will be returned, so no extra water is required. Short-term protection can be offered by spraying the leaves and covering with newspaper, or similar.

Yellowing of leaves, particularly at the bottom of the plant and in warm conditions is another sure sign. Look for fallen yellow leaves on the surface of the compost.


HOW LONG CAN ROOTS BE IMMERSED IN WATER?

This depends on:

• soil temperature (the cooler the better)
• species of plant (bog plants can stand permanent immersion)
• plant's water requirements (i.e. how quickly it can use up excess)
• soil structure (affects drainage rate - not usually a problem unless extra clay is added - soil-based composts drain quicker than soil-less ones)
  

Most plants can cope with flooding for about 24 hours, even in summer temperatures - often up to 48 hours. Since most soils can drain in this time, over-watering should never be a problem, unless more water is applied. This is why, for most plants, it is best to water infrequently but heavily, as already outlined. This way, although growth may slow for a day or two, it will then resume at maximum rate, and all parts of the compost will have been wetted.