As we are not using soil we will need to provide the elements the plant needs to grow, generally we should try and use a hydroponic food, but any mineral salt plant food will do. Remember to use it according to the directions, as your plants will not grow any faster if you give them too much food. Nutrients are usually sold, as concentrates that are mixed with water, never pour these directly on to your plants, as they are too strong when undiluted. Generally you will want to flush your plants once per month with fresh water to remove any excess salts that may buildup. PH is important in hydroponics but electronic pens whilst necessary for active systems are not so for passive whose growers can use PH test kits for aquariums or even test tape as a cheaper option.
We aim for a Ph of between 5.5 and 6.1 in hydroponics at all times. In vegetative state we aim for the more acidic 5.5 and in flowering up higher at 5.9 to 6.1 so we get all the available elements the plant needs. We can lower the Ph making it more acidic with Phosphoric acid or we can raise it making it alkaline with Potassium Hydroxide, both available from gardening stores. The strength of the nutrient is measured either by a PPM pen or an EC Pen available from hydroponic and gardening stores. Beginners can grow simply by following the nutrient recommendations on the bottle.
There are two types of hydroponic systems, passive and active. Passive systems are the simplest and easiest to use, they are also the cheapest. You can simply get an 8-inch pot, some perlite/vemiculite mixture and a small fluorescent light and you are growing. Some people may wish to grow outdoors using this method, as the results are just as good. Passive methods of growing will usually use perlite & Vemiculite granules as a medium or other suitable materials, the plant will simply be hand-watered when the medium becomes dry 1 inch down, you can test this by sticking your finger in and checking. Another basic passive system is the wick system, again its just a pot that sits above a small tray of nutrient, there is wicks running from the tray up through the pots, keeping the mixture moist and providing food the whole time for the plant. Another option is a tub placed in a tub, make some holes in the top tub and run the wicks through into the nutrient below fill the top tub with perlite vemiculite and you're growing. The solutions in these types of systems are discarded every 3 or 4 days and a new solution is prepared.
A simple Rock-wool system can be made by getting a kitty litter tray and cutting a rock-wool slab in half so it sits inside the tray, next saturate it with mixture of nutrient solution that is ph adjusted to 5.5 and leave for 24hrs, Rock-wool is advantageous in that you can buy small plugs to plant seeds or start clones in then simply cut a hole in a larger rock-wool slab and plant straight in, the roots will grow straight through the small cube into the slab. You will need to make a hole in the bottom of the tray for the slab to drain, keep it wet and allow it to drain by placing the tray on an angle. Remember to flush the whole slab with at least 5 gallons of water every 2 weeks to prevent excess salt buildup. Rockwool slabs can also be used in Ebb and flow tables where a pump floods the table to a particular height then it over flows through a tube back to the tank below, after the pump turns off the tray drains back through the pump hose. Pots with expanded clay pebbles can also be used in systems like this, watering is controlled by a timer attached to the pump and is generally turned on for 15mins every hour or more. We only need use 8 inch pots in our systems unless massive plants are our goal as the plant is always delivered what it needs, an overall highly efficient method of gardening.
Active systems are those that use a pump to in some way circulate the nutrients, this can be as simple as a 10 gallon tub below containing the nutrients, and a tray above with 6 or 7 pots in it, a tube runs from the pump in the tank below up to a smaller hose that runs to each of the plants, a hole in the bottom of the tray allows the nutrient solution to run back down to the tank. DWC or Deep water Culture gardens have pots or tubs that are suspended 1 inch over nutrient solution, an aquarium bubbler is placed below the bottom of the plant and bubbles feed the plant the air it needs whilst its constantly in nutrient meaning that the growth can be extremely quick this also is possible with high performance aeroponic and the Quantum Hydroponic gardens.
All active systems perform well, but can be costly to setup initially, the advantages is that the nutrients are either periodically or continually pumped and delivered to the plants resulting in very fast and lush growth and flowering. These systems will require more daily work than the passive systems but are not overly hard to master with patience and practice. Aeroponic systems often have small 6 inch pots filled with expanded clay or pea gravel, the roots grow in netted pots down into opaque tubs or tubes and small misters spray micro fine droplets of nutrient solution that are absorbed by the plants. We can buy small aquarium bubblers with tubes and bubble air through our nutrient solutions to keep them balanced. Optionally we can use aquarium heaters also to heat the solution to around 75° F or 21° C.
No matter what method we choose to grow our plant or plants there are a few things we should remember about hydro grows. Plant mediums should never be saturated for extended periods of time, this is especially important with Rockwool slabs and Perlite/Vemiculite pots, too much water can cause death (the plant will drown). We don't over feed our plants to make them grow bigger buds either, marijuana plants will only take what they need and cannot be force fed, too much nutrient just means burnt leaves and poor health. In the garden we regularly remove dead leaves and make sure the plants are healthy and bug free. Some green algae may grow on the medium, we can prevent this by covering our Rock-wool slabs and our pots with black plastic to prevent the light from reaching it, harmless but annoying.