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Proper Watering of Plants

Posted by Gordon Redman on 4/1/2016

Believe it or not, watering is the hardest thing for gardeners to do. Most gardeners, at one time or another, have had a preconceived idea that all you have to do is throw a little water in the plant’s general direction and you're done. This misconception can ruin the harvest or keep the blue ribbon from being awarded.

Imitate the effects of natural rainfall by adding water to your water. For small applications, fill up milk jug half way with water. Place the cap ON it and shake vigorously for a minute or two. Now the water has air in it. For grander applications, an air pump with air stones or water pumps can add air to larger drums or reservoirs. For automatic watering systems, spray stakes or spray emitters will force the water to pick up air the same way water picks up air as it falls from the sky in the form of rain. The above methods will re-oxygenate the soil for healthy roots and microorganisms.

Water the plant. Then let the plant’s soil go from wet to moist before watering again. This will prevent you from over watering or suffocating the roots causing root rot and eventual plant death. Some varieties of plants like to have their feet go almost dry to the point of slight leaf wilt before watering again. You may have to experiment with your watering cycle to find the best results for each plant variety. Log the facts you learn about your plant varieties for future reference. With a watchful eye your plants will tell you when and how often to water. Its a good idea to assign several test plants with different watering techniques. Some you water often, some you water seldom and some you water in between. Taking the time to find out how much water your plant wants will help you understand each variety of plant and become a true master gardener.

Another good idea is the use of a drip tray under the pot. When watering, drip trays work well to catch drips after you have seen what looks like to be the last of the waste-water run-off* come out of the pot. Be careful the plant doesn’t stand in waste-water for long lengths of time. This will reduce the oxygen content of the soil and can possibly cause root rot to occur. Watch your plants for signs of overfeeding if your plant is sitting in a drip tray and you haven’t been careful to see waste-water run-off of approximately 10-20% of the water applied to the soil.

*Waste-water run-off refers to water exiting the pot, never to be used again for that pot. Do not let your plant sit in waste-water. This is especially true if you use plant foods when you water. Waste-water may be used to fertilize outdoor plants.

General Rule of Watering

A good rule to determine how much water is needed at every watering is to determine how much waste-water run-off occurs. At each watering, calculate the waste-water run-off from each pot to be approximately 10-20% of the water applied to the soil. Keep watering until you get 10-20% run-off. The idea here is to make sure that the soil does not build up too much soluble plant food generated by the naturally occurring beneficial microorganisms found in all soils and/or the plant food that you are using.

If the soil dries out to the point of being bone dry, it may channel water down the side of the pot without hydrating all of the soil. If this has occurred, slowly water the plant little by little until the soil has expanded back and is uniformly moist. Keep the soil surface even and level so the water penetrates the surface evenly. Apply the water evenly to the entire soil surface.

Remember, waste-water run-off should not be allowed to soak back up into the pot’s soil. Waste-water may be used to fertilize outdoor plants.

General Rule of Flushing

If you are not able to make sure a 10-20% run-off is coming from your plant’s pot when watering, you should flush your plants every three weeks just like a good rainfall does outdoors.

Exactly how little water can be used and still have a good flush? A light periodic flush every month is a good place to start. Lets say your plant is in a 5-gallon pot. Water the soil with enough water until you see at least 25-50 percent of the 5-gallon pot capacity come out of the bottom and run away. In this case it would be 1.5 to 2.5 gallons of water. Calculate it this way; 5 (pot size in gallons) times by .25 (percent of flushed waste-water run-off water needed) = 1.25 (1 gallon of water you want to run out the bottom of the pot never to be seen again).

If you think you might need more waste-water run-off than a 25 percent flush run-off, increase to 50 percent or more and log that information into your logbook so you can remember what you did for your next grow.

When plants show signs of nutrient deficiency they may very well need more plant food but make sure you haven't overfed them first. Divide the plants that look like they are underfed into two groups or better yet if they're not too far-gone, select two plants that represent the two groups. Feed one plant and flush the other. Use a careful eye to watch for signs of improvement or further problems.


For those who put fertilizer in your water, it is important that you take care not to over-fertilize your plants. The 10-20 percent run-off rule is going to help you greatly. When you add fertilizer to the water, the plant food goes into the soil.

What’s not good is when the plant food builds up in the soil. Osmosis allows the plant to pull in the soluble plant food from the soil because the plant fluids in the roots are stronger in minerals than the soluble plant food in the soil. If the soil builds up plant food to the point where the soil has more soluble minerals in it than the plant roots have in them, the soil will actually pull minerals out of the plant’s roots. The plant can no longer feed and an interesting thing occurs. The plant shows signs of both overfeeding and underfeeding. To the untrained eye, the symptoms can be interpreted as the plant needing more plant food because it shows signs of being underfed. This leads many gardeners to add more plant food to the soil and make matters worse.

Once you have determined that you are not overfeeding your plants or you have taken the steps to flush the fertilizers out of the soil you can start your fertilizer program again with caution and a watchful eye. You most likely will never experience overfeeding again because now you know how to feed them and what to look for if you have.

The American Heritage® Science Dictionary. Osmosis (ŏz-mō’sĭs): The movement of a solvent through a membrane separating two solutions of different concentrations. The solvent from the side of weaker concentration usually moves to the side of the stronger concentration, diluting it, until the concentrations of the solutions are equal on both sides of the membrane. The pressure exerted by the molecules of the solvent on the membrane they pass through is called osmotic pressure. Osmotic pressure is the energy driving osmosis and is important for living organisms because it allows water and nutrients dissolved in water to pass through cell membranes.

I will take this opportunity to tell you some classic symptoms that plants will show when they’re being overfed.

Leaf: The plant leaf will tend to show signs of stress by turning a very dark green and then turning to a light green fading eventually to yellow. Initial stress can also be seen in the leaf as a slight buckling, or the plant’s inability to keep its leaves flat or inability to keep the classic even shape of all of the leaves. The leaf may even show signs of obvious deformity. Plant leaf tips may start to curl, either from side to side or curl up or down. The leaf tips may turn brown, dry and crumble. New leaf shoots may show signs of yellowing, either in the veins or between the veins. Advanced signs of over-fertilization will take on the same signs as severe under-watering/drought.

Stems: Stems will show signs of mineral deficiency by displaying different color stripes running up and down the main stem or/and running from the main stem to the branches. The branches will lose their ability to bend and bounce back to their original position. They will tend to break, fracture and split under pressure.

Roots: Roots will generally not give signs of over-fertilization. I will say this however; those who have over-watered the soil by letting their plant’s pot sit in waste-water may develop root rot. With root rot, the roots will turn brown and mushy. You will see many of the same symptoms as mentioned above as the plant's root lose their ability to uptake nutrients.

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