Water and plants
Watering would appear to be the simplest task when it comes to growing plants. We have readily accessible water straight out of our tap that is clean, low in salts and disease free. However, probably the easiest blunder to fall into is providing too much or too little water to our plants and crops.
Farmers growing broadacre crops that are rain fed don't have to deal with this problem, they measure what they receive which determines their fertilizer applications. Growers who have access to irrigation for their horticulture crops, veggie gardens or manually water their indoor plants need a general idea on how much to water their plants which can be easier said than done. Some water on a weekly or daily schedule, some do it when they remember and others when the pot looks dry.
Why is watering so important?
The best reason I can give is to provide the ideal environment for the roots in the soil, too much water can drown the plant by waterlogging the soil and removing all the air in the soil, consistently having excess water or wet soil for prolonged periods of time will encourage soil diseases to thrive, the most common ones are root rot and fusarium. Not enough and the plant will close it's stomata (little breathing holes in the underside of the leaf) to reduce dehydration but this results in the plant being unable to breath and convert carbon dioxide.
For a majority of plants, you want to water the soil up to the point where it can hold no more, if you see water draining out of the bottom of your pot you've applied too much, but at least the hole can provide for some good drainage. To know when to water again simply put your finger into the soil and pull it back out, if you finger gets cool and you have wet/moist soil sticking to your finger you need to wait longer. By allowing your soil to dry out in the top inch you're preventing soil borne diseases and fungus gnats, which are tiny insects that you commonly find flying around and on the soil of indoor potted plants.
The most common reason for dying indoor plants in my experience is root rot. My friends and family will water too much and too frequently that the bottom of the pot will contain soil that holds no air, when this happens the smell will resemble something that is rotting. Why does it smell bad? when you over water frequently the air from the soil is removed and this causes a change in the microbiology from bacteria and fungus that breath air to bacteria and fungi that function without the presence of oxygen. The microbiology will go through anaerobic processes that give off a rotting aroma and from my experience does not go well with most plants or crops...unless you're trying to recreate a swamp.
How to measure soil moisture
Farmers with access to irrigation must make decisions on when to water their crops to optimize yields. To determine how much water to apply and when, is done by measuring the water content of the soil using different instruments. Some instruments determine water content through pressure and others via electrical current. All instruments are useful but all have their drawbacks. This is called moisture monitoring and can prevent a world of pain especially if you own an avocado orchid or want to get the best out of you banana plants. Typical soil moisture monitoring instruments are tensiometers or water content meters.
Factors affecting irrigation timing and soil moisture
Sunlight and temperature
Depending on where you live or where you place your plant will determine the rate that the water is removed from the soil. As you expose your plant and the soil the plant is in to sunlight the more the plant can photosynthesis. The more a plant can photosynthesis the more water it will use to continue growing and utilising sunlight. For most cropping plants, the ideal growing max temperature is 24-28 degrees, this means the plant is at its most efficient and will utilise water and nutrients faster and grow quicker. Of course, there are plant species that have preferences out of this range so do not be too quick to assume ideal conditions.
Plant Age
How large and old your plant is can determine the water requirement and uptake speed. A tomato seedling can be watered once or twice a week in its first few weeks of growing, but once it has started producing fruit and is over a metre tall may require watering everyday when in ideal conditions. It is easy to over love a new young plant but this can be detrimental to it's health. Seeds may require more attention depending on how deep you seed them!
Crop and phase
Crops and plants go through different life cycles, sometimes called phenological stages, which describes what the plant is doing in that particular time. Tomatoes for example are a crop that usually last no longer than a year, unless you're in a green house. They grow vegetation for the first month or two before going into a reproductive stage where they produce flowers and fruit. Depending on the life cycle can determine the demand for water, for most crops water demand is at it's greatest when the harvest is being produced.
Soil texture
Soil texture! is it sand or clay or silt? the sandier your soil is the more frequently you'll need to water your plant, the more clay there is the less frequent more large volume your watering will need to be. Sandy soils are great because they will less likely hold soil disease because of good drainage but wont hold water for long meaning once you come back from your holiday you plants are either dead or dying for a drink. Clay or heavier soils require less frequent watering and are more prone to waterlogging but provide the greatest yield potential due to the ability to hold much more nutrients and water in the soil.
To Conclude...
Each crop has their own demands and each will constantly vary their uptake! But with a few tools you can get an idea on what the water demand for your plants can be and why the uptake has been faster or slower than usual. If you overwater don't stress, most plants are happy enough to have their roots in waterlogged soil for a temporary amount, some people even keep their plants in a jar of water alone!
Happy growing.