How to grow hydro is really about how to maintain your nutrient reservoir. After all, there is nothing you can do to MAKE your plants grow. You can only provide all the best conditions, sit back, and let plant growth happen. Assume your plants are getting enough light and air, and are kept at a good temperature. Plant growth will happen (often quickly) as long as you provide the best conditions in your nutrient solution (and in the rest of the grow room) everyday!
Learning how to grow hydro starts with your beginning water quality. Check your tap water with a TDS meter. Anything over 200 ppm and you should probably use a reverse osmosis filter, or else use bottled spring water. While not necessary, it's not a bad idea to treat your water using hydrogen peroxide.
If you really want to complicate things, you can get a complete water test. In this case, you can use tap water with up to 300 ppm as long as no more than 150 ppm of the total is from Calcium, Calcium Carbonate, and Sodium compounds.
Through the water, the plants will receive all of their food. This water needs to contain primary nutrients (N-P-K), secondary nutrients (Calcium, Magnesium, Iron, Sulfur), and all trace nutrients. I strongly recommend using a professional hydroponic nutrient product for this.
In addition to regular food, there are a few additives that make a
huge difference in the healthy development of your plants. These are
vitamins (like Thrive Alive B1), trace nutrient supplements (like Maxicrop
liquid seaweed), and plant hormones (in both seaweed and Thrive Alive red). Another
useful additive is Silica, which is used to boost the immune system of
Many expert gardening articles I have read by people who know how to grow hydro recommend adding Thrive Alive B1 and Maxicrop to every drop of water you give your plants. Use 10 ml (2 tsp) per gallon of each. If you are using a seaweed based fertilizer, it is not necessary to add additional liquid seaweed. For more information on feeding and maintaining your nutrient solution, check out the hydroponic nutrients page.
If you want to learn how to grow hydro well, you must know about the pH (potential Hydrogen) scale. Hydroponic nutrients are only usable to your plants when the pH is right. The maximum amount of nutrients are available to your plants in a range of 5.5 pH to 7.0 pH. In hydroponics, the nutrients are often kept around 5.5 because the plants absorb nutrients slightly more quickly at this pH.
Also, the natural tendency of the nutrient solution is for the pH to creep up slowly over time,
so it is a good idea to adjust the pH down to the low end of
the acceptable range whenever you make a pH adjustment.
People that know how to grow hydro use a total dissolved salts (TDS) meter or an electrical conductivity (EC) meter to tell how strong or how weak the nutrient solution is. The ideal strength of your nutrient solution depends on what type of plants you are growing, and also what stage of the plant life cycle they are in. Your plants will tend to require stronger and stronger nutrient solutions as they grow more mature, and especially when they go into flowering. Check out the plant life cycle pages for more specific advice on what strength to keep your nutrient solution.
With a ten gallon reservoir feeding 10 medium size plants, you will need to check the strength (TDS or EC) and the pH of your solution at least once per day. People that know how to grow hydro usually use a larger reservoir. With a larger reservoir, the changes in the nutrient solution take a little more time. The larger reservoir acts as more of a buffer. A good general guideline to follow would be to use at least 3/4 gallon to one gallon of nutrient solution per plant. No matter what size reservoir you have, I would still recommend you check your nutrient solution at least once a day!
You should have a desired water level marked out somehow on your reservoir, and as your plants feed they will drop the level of the nutrient solution in the reservoir. Always begin by topping your nutrient reservoir up with plain water. It is a good idea to let any water that you use sit out overnight in an uncovered container. This lets the water de-Chlorinate, and also lets the water come to room temperature. Adding cold water can shock the roots, causing root damage below as well as damage and leaf drop above.
When checking your nutrient solution, it is a good idea to check the nutrient solution strength first (as opposed to checking the pH first), because the addition of nutrients and supplements to the nutrient solution will usually change the pH of the nutrient solution a little. If the nutrient strength is low, add a little more of your base hydroponic nutrients. If the nutrient strength is a little high, add plain water.
Once the strength of your nutrient solution has been tested and adjusted, it is time to test the pH. The cheapest way to do this is with a small bottle of pH indicator drops....you just scoop up a sample of your water, add a few drops of indicator, and shake! Just check the results against the color chart on the bottle for your pH.
If you test your nutrient solution and the pH is up, then slowly
add a little pH DOWN.
If your pH is too low, then slowly add some pH UP.
After two weeks of using the same nutrient solution, it is time for a nutrient change. The plants may have been using some nutrients faster than others, and now you might be heading for a nutrient imbalance.
Keep an extra nutrient reservoir full of plain water waiting for your
next nutrient solution change. This ensures you will have
de-Chlorinated, room temperature water that will not damage your plants'
It is a good idea to run a tank full of plain water (or 1/4 strength nutrient solution) through the hydroponic system for a few hours in between nutrient changes. This helps to flush out any nutrient buildup. Some experienced gardeners do this every four weeks, or every other nutrient change. The addition of enzymes, such as Hygrozyme, will help with the flushing process, and can actually be used DURING the growing process to prevent nutrient buildup in the grow media. Whenever you find your hydroponic system and plant containers empty, consider using hydrogen peroxide to keep things clean and healthy.
Once you have a simple feeding plan that is working well, you can try to maximize your results. The best advice here is to make small changes, one at a time,
and to let each change show its effects before making another change.
Sometimes this will mean waiting two weeks, other times it may mean
waiting a whole crop cycle for the results. This is where keeping a journal for the garden can really pay off!
My experience has shown that a simple plan with high quality results is what your goal should be. Many times, experimenting only leads to bad results. Over complicating things. To make matters worse, if you changed two or more things, you have no idea what is causing the problem now. Anyone interested in a final tweak to push their plants the extra mile should learn more about these fertilizer and soil additives.
Pros that know how to grow hydro usually do a final flush just before harvest. This can be done by replacing the nutrient solution with plain water for the last 7 to 10 days. It will help if you change the water each day with fresh, plain water for these last few days. An alternative is to use a product specifically made to help flush out these nutrients, such as Final Flush or Flora-Kleen.
A common mistake is to give plants just plain water during the flushing process. It IS desirable to flush nutrient salt compounds from the plant tissue, which is exactly why you do NOT want to include fertilizer during the flushing process. However, many plants continue to add plant weight and continue to develop tasty plant esters, amino acids, alcohols, terpenes, and resins right to the end.
example, a plant puts on the last 10% of these compounds in the last 10
days of flowering. If you are giving your plants only plain water for
the last 10-14 days, you may be preventing your plants from coming to
their full potential. I recommend the addition of B1 to continue driving
cell division, as well as an additive that will provide esters and
plant alcohol precursors, humic acids, amino acids, some
carbohydrates....such as Liquid Karma (the original is my personal
favorite) or Sweet. 10 ml per gallon of each is an effective rate of
application, and is the rate that I use.
Flushing the crop helps remove any fertilizers in the plant tissue. Flushing properly will improve the flavor, aroma, and potency of the finished produce coming out of your garden.