The philosophy driving the thinking on this method of watering is to provide the optimum environment for the root system for the maximum amount of time each day. Trying to balance the air-water relationship and the nutrient level along with the nutrient balance so that the root system and the plant have as healthy environment as you can provide. Many commercial hydroponic growers feed their plants every 30 minutes with 60ml each watering from when the light comes up until 2-4 hours before it goes down. The goal here is to provide your roots with the optimum level of moisture & air supply at the time of feeding.
The most important elements we want to optimise are moisture, air and the nutrients balance. All three are closely tied together. When the media is too wet you are short on air and when the media is to dry the EC goes up, which growers would usually link to the nutrient level going up – the amount of nutrient does not actually go up, just the concentration but that is a topic for another time.
Water and air balance
If we define “to wet” as not enough air (roots are stressed and root damage occurs) and “to dry” as the plant leaves are flagging because the media does not have enough water to give to the roots. (This lack of moisture should not be confused with the flagging of leaves that occurs when media is obviously moist enough and the leaves are flagging from lack of roots to transport enough water for the amount of leaves the plant has. Somewhere in-between these two points the water and air supply are at an optimum. If we can find that point and give water at the same rate that the media is losing water (plant use, evaporation, drainage etc…) we should be able to maintain the air-water balance and grow a very healthy plant. The more often you are watering and the less water you apply at each watering the better chance you have to maintain that balance – If vapour pressure deficit is used as a measure of the water needs of a plant you may be adjusting the water regime several times an hour. We won’t go into Vapour Pressure Deficit right here but if you do fancy digging in a little more check out this page. There are loads of sites out there. Most growers actually use their sense of sight and feel to make these judgements – by just using your natural senses, an experienced grower often makes adjustments several times a day to maintain that optimum balance – practise makes perfect or at least it gets you closer to perfect.
Nutrient levels and nutrient balance
The amount of nutrient and the nutrients balance are difficult to watch on a day-to-day basis. If you are using a well-balanced nutrient solution and a more regular short & frequent feeding regime, then there is less chance that the plant will run out of a particular element because the complete balance of elements is continually being supplied. Knowing the level of nutrient is relatively easy by taking an EC reading (EC just measures the amount of salt). To know the actual balance of the nutrient in the media you would need a lab analysis of the media which is obviously not going to happen for most growers.
There are a number of factors that make maintaining that balance difficult. Knowing what the plant water and nutrient usage is for growth; knowing how much run-off is needed to keep salts down in the media and knowing how much evaporation the plant has are the primary three factors that come to mind. Knowing what values to use for these factors is not easy but I would suggest that no matter what the ‘need’ is, using a small and frequent watering regime allows you to make adjustments as the day goes by. If the day starts out warm and sunny then turns cool and cloudy the plant’s needs change. Your environment both indoors and outdoors can be susceptible to change for a variety of reasons. It is easier to see moisture needs than the nutritional needs. If you are watering once a day or once in three days the 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 would be inhibited in its growth potential. If watering several times a day, all of the elements are renewed within a few hours so you can see these changes much quicker.
Distribution of water and nutrient
Let’s just talk about the water distribution because where the water goes, the media can be flushed and the nutrient solution goes. I will talk about the distribution from two points. The length of time it takes to give the water and the number of points the water is delivered too.
The speed that the water is applied determines how much it spreads sideways and how much it goes straight down. If the water is applied very fast, you get a good broad coverage on the surface but not necessarily very deep or wide. If you apply the water at the same speed that it soaks into the surface you will get a deeper coverage but not necessarily very wide coverage. If you apply the water 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, then you can get a greater coverage both in depth and sideways. This helps to allow root growth throughout the growing media, giving a constant supply of moisture and nutrients as well as reducing the build-up of salts. Many commercial growers use drippers so that the water and feed solution literally drips onto the media taking 1-2 minutes to apply 60 ml of water.
If you give a half-gallon of water to a pot (or a plant in the ground) that is about 15inches in diameter, in 10 seconds or less the whole top of the pot will become wet and the media that is close to the pot on the sides. The media that is 1inch in from the side half way down the pot may be dry. If you take that same half gallon and divide it into 8 equal parts (1 cup) and every hour pour the cup of water slowly onto the media you will get a much more uniform distribution of the water and nutrient.
The number of points that the water is applied to in each plant also has a big influence on how well the water is distributed. A 15inch pot with one slow dripper would take a long time to apply enough water and would not distribute it very well – there is a limit to how far water will travel sideways in growing media. But if you put 4 drippers evenly spaced around the top of the pot your water and nutrients will be distributed quite evenly.
This is a way of thinking about watering; each set-up has to work out the details of how much water is given and how often it is applied. You have to take into account the size of the pot, size of the plant, temperature, amount of air movement, the type of growing (how much water it holds), etc. to work out the exact plan. And of course it takes lots of trial and error. Again practise makes a better grower. Don’t expect to get it right in the beginning – failure teaches us to perform better.
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