Answering the question, “How much water do plants need?” is a lot like answering the question, “How much food does one person need?. The answer relies on a string of variables. Different people require different amounts of food. Different plants require different amounts of water.
Size matters. When assessing the hydration requirements of a plant, take into account its size. Picture the water being absorbed by the root system and traveling up the stem and into the leaves. Taller plants will need more water applied to the roots in order to achieve proper hydration to each stem and leaf of the plant. If the plant is a fast-growing variety, higher amounts of water will be needed to support the rapid growth. Stems, stalks, trunks and branches are like drinking straws. The water from the roots travels up these tubes, carrying with it all the nutrients from the soil. The taller the plant, the more it must “drink” to allow that water to travel further up to the top.
Find out what kind of root system the plant has before determining its water requirements. Some plants put out shallow roots or runners directly under the surface of the ground. The spreading root system allows the plant to be anchored in strong winds, and it also enables roots to soak up surface water more readily. Shallow root systems are common in plants that grow naturally in hard or rocky soils. Creeping ground-cover plants, vines and bushes often have wider root systems that spread just below the surface of the soil. These types of plants will require a more frequent watering schedule, but the amount of water per application should be fairly minimal. Envision the roots under the soil as you water the plant. Water in a broad pattern, enabling all of the soil around the base of the plant to become well-moistened. Soils that drain easily like sand or loam will accept more water. Dense soils will hold the moisture like a sponge. Over-watering will cause root rot and fungus, a sure recipe for disaster.
Plants that put forth a tap root require a longer watering cycle. Water these plants less frequently, but apply more water per watering session. Again, a “mind’s-eye” approach is best, picturing the plant’s root system absorbing the water as it seeps into the soil. Trickle the water from a soaker hose, or pour slowly from a watering can. This allows for percolation to take place rather than a fast run-off. Taking into account the soil’s composition is crucial to getting good results. Hard, compacted soils will not percolate water easily. Aerating the soil prior to watering can help to allow water to permeate the surface and reach deep roots. Use a claw tool or garden hoe to loosen soil near the base of the plant, being careful not to damage the plant’s structure.
A final element in determining a plant’s needs is environment. Humidity levels in the environment will play a huge part in a pant’s water requirements. Once again, a certain level of common sense and imagination is necessary in assessing environmental factors. Tropical climates are steamy and humid, hydrating plants and soils through the water droplets that hang in the air. If heavy dew is present each morning, the humidity is high and the plants are receiving natural hydration each day. Dry air and windy conditions indicate low humidity and a greater need for artificial water sources.
Don’t forget to take into account the area’s rainfall amounts when determining the water requirements of plants. Of course, indoor plants are exempt from this formula, but monitoring rainfall in outdoor growing areas will help to calculate shortage or overages of water. Not much can be done when rainfall is excessive, other than ensuring proper soil drainage. If the weather is sunny and dry, be prepared to water often and in large quantity. Over-watering is close to impossible when the sun is working equally hard to evaporate your efforts.