Sometimes, we need to go back to the basics and look at our water…
So many times, as hydroponicists, horticulturists, or botanists, we look too far into a problem and try many exotic methods of figuring out why our plants are reacting a certain way. We over scrutinize the nutrients, lighting, environment, and any other area that can influence plant growth. Sometimes, we need to go back to basics and look at what seems too easy to have been missed; the water. So simple and abundant, yet we often overlook one of the most important molecules in the universe. Now let’s follow in NASA’s footsteps and follow the water…
Quality of Water
Figuring out whether you have hard or soft water is easy to find with a quick Google search of your locale. If you live in an area where the water can come from one source or another, it’s important to monitor and use the appropriate nutrients; they’re designed to either balance the calcium and the magnesium that makes water “hard,” or the lack of it, which makes water “soft.”
Very hard water areas would benefit from using a reverse osmosis filter to remove some of the minerals in the water, therefore softening it. On the contrary, very soft water area growers can benefit from adding a small amount of a Cal-Mag nutrient, which will help buffer the nutrient solution and prevent big pH swings. Lastly, if in a hard water area, the extra buffering from calcium and magnesium can mean it takes a lot of acid to bring the pH down to an acceptable point (5.5-6.5), so using a nitric acid pH down solution during vegetative growth, and a phosphoric acid pH down during flowering can help with plant growth at different times of the life cycle, while still maintaining the lower pH levels.
The pH of water needs to be between 5.5 and 6.5 for optimum absorption of nutrients. In hydroponics it’s best between 5.5-6.0, coco prefers 5.8-6.3, and soil likes 6.0-6.5. Common errors with pH include growers being too strict with a specific pH number, and adding large quantities of pH up or down. This will lock out other nutrients and cause deficiencies, while in reality, it’s good to let the pH swing a little between acceptable values so the full spectrum of nutrients have an opportunity for complete uptake.
Possibly the most common mistake that any grower can and will make. The term ‘over watering’ may seem a little pedantic, since technically speaking it is impossible to ‘over water’ a plant. It is however, entirely possible to run SO much water through a plant medium, that it pushes all of the pockets of air (oxygen) out and suffocates all the roots of the plant. This, single-handedly, is the number one mistake when cultivating any plants, and if allowed to continue, will surely cause a succession of deficiencies and plant abnormalities. In the most severe of cases, it creates a breeding ground for pathogens, and the root zone becomes an anaerobic playground for Pythium and other root disease monsters.
Under-watering can just as easily lead to plant wilt and death as over-watering can, however, even some of the most horrific looking plants can come back from the brink when given a healthy dose of H20. With the option of automatic feeders, gravity feeding systems, and timers, there really is no excuse for any plant to lack water to the point of wilt. To hit home the point of under-watering, the plant will close its stomata during periods of drought, and essentially stop all processes to conserve what little water it has left. Your plant is in suspended animation until you water it, or it dies!
An easy mistake to make is thinking that water temperatures really don’t matter that much. Get the water out of the tap, add nutrients, check EC, check pH, and feed. Right? Well, a few days later, the grower is left wondering why they’ve got deficiencies or root problems. When too warm, the amount of oxygen decreases dramatically, creating a breeding zone for anaerobic bacteria, such as Pythium. If too cold, the plant is unable to take up nutrients efficiently, specifically phosphorus. The “Goldilocks” temperature for water is 18 degrees Celsius or 64 degrees Fahrenheit. At these temperatures, the water is cool enough to hold sufficient oxygen, but also warm enough to allow good uptake of all available nutrients. Keeping an eye on water temperatures can prevent root rot and other rhizosphere pathogens.
The error of many a grower is not fully understanding the importance of oxygenation at the root zone. Whilst knowing that the roots require an oxygen rich (aerobic) environment, many growers will still saturate the media with water (over-watering), and forget a plant’s basic physiology needs. Therefore, getting the watering technique just right is essential for a healthy crop, and to do so, you need to understand the system that you use, whether that is simple hand-feeding, or a sophisticated deep water culture system.
The most basic watering technique used throughout the world by millions of gardeners, and still one of the most effective when done correctly. Two types of hand feeding exist in the hydroponics industry – top feeding and bottom feeding. Top feeding allows the water to soak the top of the media and drain down, irrigating the roots along the way. Bottom feeding, usually used when the plant already has an established set of roots, allows the roots and the media to wick the water upwards through the pot, using the amount of water that each individual plant requires, rather than a one-dose-fits-all type approach that can be the downfall of many top feeders.
Top feeding, however, when a plant is young and lacks an established root zone is the best practice. A common mistake when top feeding is to just drench the pot with a lot of water, which over time will compress the media and effectively push all the air pockets out of the pot. You’ll know if you’re doing this, because one day you will think someone has stolen 2-3 inches of media out of all of your pots. They haven’t though, in reality you’ve just been a little overzealous with the top feeding. Toss out the pressure nozzle for the hose and start lightly drizzling the media from the outside inwards, almost like a gentle rain.
A second mistake that top feeders typically make is watering with just barely enough to saturate the media and roots. Over time, this will lead to an accumulation of nutrient salts, and will throw your EC/PPM/Cf readings way off. Always make sure that with each new watering, there is sufficient water being pushed through each pot, so that it “flushes” out any excess salts from previous irrigations. Lastly, it’s always good practice to flush with plain, neutral water at least 3-4 times per cycle to remove the accumulation of salts that occur, especially so in warmer environments.
Bottom feeding is supposedly not just better for your plants, but also easier to implement in a smaller garden. Bottom feeding into individual saucers is very exact, however those with larger gardens will typically make a deep tray for a collection of plants to feed simultaneously. The biggest mistake when using this method is to leave excess water in the saucers or trays, putting the root zone into anaerobic conditions. When done correctly, the media will absorb what it can to keep the root ball moist, with any excess siphoned off for the next irrigation. After a while, you should know roughly what the plants are actually drinking, allowing for more accurate amounts of water, no waste, and no stagnant plants.
Moving away from hand watering to a complete system can make your life a dream, or a nightmare, depending on how it is approached. Typically, growers will move from hand feeding to a flood and drain system for ease of use, and potentially healthier, more productive plants. The most common mistake made in flood and drain systems is to think the system will do all the work, while the grower sits back and relaxes… Mistake number 1!
It can take some time to configure a flood and drain system correctly, but the time spent here will pay dividends over the coming months. Firstly, you need to consider the media that will support your plants. Two common choices are clay pebbles and a pebble/coco mix, typically 60/40. From here you need to decide on irrigation frequency, irrigation height, and irrigating time.
Common errors in flood and drain systems include:
- Increasing or decreasing irrigation frequency, because your calendar says it’s been maybe 2 weeks since you’ve last increased the cycle, and now it’s time…
- Not changing the irrigation frequency at all throughout the grow/bloom cycles.
- Your plants are showing signs of stress, so therefore you water them more frequently without doing a proper diagnosis.
- Watering often typically increases yield and size, so you water all day and all hours of the night without measuring.
Avoid these common grower mistakes by making sure you follow proper irrigation techniques, it will save you a lot of headaches in the future!
Pebbles will require more frequent irrigation (low water holding capacity) compared to a pebble/coco mix, which will require less frequent irrigation (higher water holding capacity). The second part to consider is the current stage of plant growth, as young plants need less frequent irrigations compared to mature plants. Third, we have our environment to take into account. During early vegetative growth, the temperatures should be lower than in flowering, and the humidity should be higher, therefore transpiration levels are relatively low, and the plant will require less watering cycles (cool with high humidity). Mid peak to flowering, temperatures are higher and humidity tends to drop, which increases the transpiration rate and means the watering frequencies also need to increase.
There are no absolutes when it comes to irrigation frequency. What works for you and a particular plant and environment may not work for somebody else, so start with 2-3 irrigations a day* in pebbles, and 1-2 irrigations a day in pebble/coco mixes for young plants. Adjust as required for the environment, and keep a record of irrigation frequencies for later adjustments and future growing. Plants showing signs of growth, and root systems becoming fully established are good indicators to increase the irrigation frequency.
*A “day” being when the lights are on, whether this is 24 hours, 18 hours, or 12 hours.
Irrigation Height and Duration
A common mistake with irrigation height is not making sure the pots are on an even surface. Having some pots higher or lower than others results in different flood heights, over-filling some pots and under-filling others. Make sure your floor is level, this can be done easily by filling the pots by initiating a flood cycle.
While checking the flood height it’s good practice to time the cycle, to avoid mistakes of not allowing all the pots to properly fill during the flood, or leaving water in the flooded state for too long. If the floor is uneven, it’s probably worth investing in trays that will raise the pots up off the floor, tilting them slightly to improve draining. These are then much easier to manipulate, and ensure all pots are the same height. Flood height should reach roughly two-thirds of the way up the pot. Any less and you risk not keeping all the roots moist, too much and you may keep the media, such as coco, wet for too long.
A good irrigation duration for pebbles would be a couple of minutes before draining. For pebble/coco mixes, once flooded to the correct level, it needs to drain immediately to prevent diseases, such as root rot, from lack of oxygen. For a healthy, productive plant in a flood and drain system, you need to apply a hand feeding mentality of daily checks and investigation to the system. Only then will you see the improvements flood and drain systems have to offer.
Common mistakes when watering or irrigating an NFT system include not using any spreader mat on the tray to help evenly distribute the flow of water. A spreader mat will ensure the water forms an even layer, and if allowed to drape over the edge, will remove any trickling effect. Stealth is wealth in this instance.
At the beginning, leaving the water pump on 24 hours a day before the roots are properly established can lead to ‘over-watering’ the rock wool. Immature plants do not have the root system to take up water like more mature plants, and so, require reduced irrigation. Either putting the pump on a timer or manually turning the pump on once a day for a couple of minutes to soak the rock wool is good practice at the beginning. The dry period will allow the roots to search, producing a healthier root mass.
When the roots and plants have matured (the rock wool is covered in roots), the pump can be left on 24 hours a day. A good amount of water to pump through is roughly 1 litre a minute, but again this depends on how many plants are being grown, the size of the channel, and the environment.
There are two common mistakes in DWC, and unfortunately, not addressing either one of these will seriously hinder your plant’s growth. The first is using water that’s too cold, or too warm. The second is not oxygenating the water adequately enough. If the roots sit in water that’s too cold (below 150C/ 590F), it will not take up nutrients. If they are in water that’s too warm (above 220C/710F), the water cannot hold enough oxygen. The “golden point” is at 180C or 640F. At this temperature, we achieve a good level of dissolved oxygen and nutrient uptake.
For good oxygen levels, simply moving the water around is not sufficient for increasing dissolved oxygen in the water. To do this, the surface tension of the water must be constantly broken to allow the oxygen to dissolve in. This can be done with air stones, air curtains, or a pump that pushes water to the surface and breaks the surface tension.
As you’ll notice with DWC, it is impossible to ‘overwater’ as the roots are constantly submerged in water. The term overwater technically means that the roots do not have access to enough oxygen (the water has displaced the oxygen). You will notice that in the systems mentioned above, oxygen is always the critical factor when setting irrigation cycles or flood frequency, and it should be the number one point to keep in mind when irrigating any type of plant – in a system or hand watered.
To finish, if a cultivator is attentive, passionate, and open-minded, they will only make these mistakes once before learning from them, and making changes. Nothing can replace a perceptive grower, and that is the number one piece of information to take away from this article.
By Stephen Brooks, NPK TECHNOLOGY . Excerpt from Garden Culture Magazine