Making the Case for Shorter, More Frequent Watering
For every new set-up, growers have to work out the details of how much water to provide their plants, and how often it is applied. They have to take into account the size of their pots, size of their plants, temperatures, level of air movement and the water retention of their growing media, then work out a plan. Mark Wittman makes the case for making shorter, more frequent watering through the use of automation a big part of your watering strategy.
Shorter, more frequent watering provides a better environment for a plant’s root system for the maximum amount of time each day. It is a popular method of watering that attempts to balance the air-water balance and nutrient levels so root systems and plants have a healthier growing environment.
The most important elements to optimize in your growing environment are moisture, air and nutrients, and all three are closely tied together. When the media is too wet, you are short on air and when the media is too dry, the EC goes up. Some growers link a higher EC to a higher amount of nutrients, but the amount of nutrients does not actually go up, just their concentration.
Many commercial hydroponic growers feed their plants every 30 minutes with 2 oz. of water, starting when the lights are turned on and lasting until 2-4 hours before they are turned off. Their goal is to provide roots with optimal levels of moisture and air supply throughout the day. Here’s a closer look as to why I believe this is a better approach to watering plants.
Air-Water Balance in the Root Zone
When plants are too wet, their roots can’t get enough air. Roots become stressed and root damage occurs. When plants are too dry, their leaves begin to dwindle and weaken because the media does not have enough water to give to the roots, although this lack of moisture should not be confused with the weakening of leaves that occurs when the media is moist enough, but there are not enough roots to transport water to the leaves.
Somewhere in between these two points, the water and air supply in a garden are at optimal levels. If you can find that point and provide your plants with water at the same rate the media is losing it through plant uptake, evaporation and drainage, you are on your way to maintaining the right air-water balance and growing healthy plants.
The more often you water, and the less water you apply at each watering, the better chance you have to maintain the right air-water balance. Some growers use something called the vapor pressure deficit to measure the water needs of a plant, but in doing so, they might find they are making many labor-intensive adjustments to their watering regimen throughout the day.
As an alternative, most growers use sight and feel to make these judgements. Just by using their natural senses, an experienced grower often makes slight, easy adjustments throughout the day to maintain the optimal balance. Practice makes perfect, or at least gets you closer to perfect.
If you are using a well-balanced nutrient solution and a shorter, more frequent feeding regimen, there is less chance your plants will run out of a particular element because the complete balance of elements is continually being supplied. Finding out the amount of nutrients your plants receive is relatively easy by taking an EC reading with an EC meter, which measures the amount of salts in a solution. To know the actual balance of the nutrients in the media, though, you need a lab analysis of the media, which is not always feasible for most growers.
There are a number of factors that make maintaining the right nutrient balance difficult. Knowing the water and nutrient usage, how much run-off is needed to keep salts down in the media, and how much evaporation the plant undergoes, are three primary factors that come to mind. No matter what your plants’ nutritional values are, using a shorter, more frequent watering regimen allows you to make adjustments as the day goes by. If the day starts out warm and sunny, then turns cool and cloudy, the plants’ needs change.
Your environment, both indoors and outdoors, can be susceptible to change for a variety of reasons. It is easier to see your plants’ moisture needs than their nutritional needs. If you are watering once a day, or once every three days, your plants may be running low on a particular element in the nutrient solution, potentially for up to two days or more. You may never see a deficiency, but the plant is inhibited in its growth potential.
However, if you’re watering several times a day, all of the elements are renewed within a few hours, and you can see these changes much quicker.
Distribution of Water and Nutrients
When it comes to water distribution, there are two main points to touch on: the length of time it takes to provide the water, and the number of points the water is delivered to.
Speed – The speed at which water is applied to the plants determines how much of it spreads sideways and how much of it goes straight down. If the water is applied fast, you get a good, broad coverage on the surface, but not necessarily deep or wide. If you apply the water at the same speed it soaks into the surface, you will get a deeper coverage, but not necessarily a wide coverage.
Here’s a better example: If you provide half a gallon of water to a 15-in. potted plant in 10 seconds or less, the whole top of the pot will become wet, including the media that is close to the pot on the sides, but the media that is 1 in. from the side, halfway down, may remain dry. But if you take that same half-gallon and divide it into eight equal parts, and every hour pour a cup slowly onto the media, you will get a more uniform distribution of water and nutrients.
If you water your plants at such a rate that the water begins to move sideways as fast, or close to as fast, as it moves down through the pot, you can get a greater coverage, both in depth and sideways. This will allow roots to grow throughout the growing media, giving them a constant supply of moisture and nutrients, as well as reducing salt buildup. Many commercial growers use drippers so the water and feed solution drips onto the media, taking 1-2 minutes to apply 2 oz. of water. They repeat this process every 30 minutes.
Distribution points – The number of points the water is applied to each plant also has a big influence on how well the water is distributed. For example, the 15-in. pot mentioned earlier would take a long time to water if it only had one slow dripper. The one dripper wouldn’t be able to supply enough water fast enough, and it would not distribute it very well. There is a limit to how far water will travel sideways in growing media. However, if you evenly space four drippers around the top of the pot, your water and nutrients will be distributed more evenly.
In summary, shorter, more frequent watering is a better way of thinking about plant watering. I stand by automating your operation for all of the reasons above. It’s not a big project, and it will increase your yields and lessen the amount of time and resources you need once you’re set up.