Most growers report that a hydroponic system will grow hemp plants faster than a soil medium, given the same genetics and environmental conditions. This may be due to closer attention and more control of nutrients, and more access to oxygen. The hemp plants can breath easier, and therefor, take less time to grow. One report has it that hemp plants started in soil matured after hydroponic hemp plants started 2 weeks later!
Fast growth allows for earlier maturation and shorter total growing time per crop. Also, with soil mixtures, plant growth tends to slow when the hemp plants become root-bound. Hydroponics provides even, rapid growth with no pauses for transplant shock and eliminates the labor/materials of repotting if rockwool is used. (Highly recommended!)
By far the easiest hydroponic systems to use are the wick and reservoir systems. These are referred to as Passive Hydroponic methods, because they require no water distribution system on an active scale (pump, drain, flow meter and path). The basis of these systems is that water will wick to where you want it if the medium and conditions are correct.
The wick system is more involved than the reservoir system, since the wicks must be cut and placed in the pots, correct holes must be cut in the pots, and a spacer must be created to place the hemp plants up above the water reservoir below. This can be as simple as two buckets, one fit inside the other, or a kiddie pool with bricks in it that the pots rest on, elevating them out of the nutrient solution.
I find the wick setup to be more work than the reservoir system. Initial setup is a pain with wicks, and the hemp plants sit higher in the room, taking up precious vertical space. The base the pot sits on may not be very stable compared to a reservoir system, and a knocked over plant will never be the same as an untouched plant, due to stress and shock in recovery.
The reservoir system needs only a good medium suited to the task, and a pan to sit a pot in. If rockwool slabs are used, a half slab of 12” rockwool fits perfectly into a kitty litter pan. The roots spread out in very desirable horizontal fashion and have a lot of room to grow. Plants grown in this manner are very robust because they get a great deal of oxygen at the roots. Plants grown with reservoir hydroponics grow at about the same rate as wicks or other active hydroponic methods, with much less effort required, since it is by far the simplest of hydroponic methods. Plants can be watered and feed by merely pouring solution into the reservoir every few days. The pans take up very little vertical space and are easy to handle and move around.
In a traditional hydroponic method, pots are filled with lava/ vermiculite mix of 4 to 1. Dolite Lime is added, one Tblspn. per gallon of growing medium. This medium will wick and store water, but has excellent drainage and air storage capacity as well. It is however, not very resuable, as it is difficult to recapture and sterilize after harvest. Use small size lava, 3/8” pea size, and rinse the dust off it, over and over, until most of it is gone. Wet the vermiculite (dangerous dry, wear a mask) and mix into pots. Square pots hold more than round. Vermiculite will settle to bottom after repeated watering from the top, so only water from the top occasionally to leach any mineral deposits, and put more vermiculite on the top than the bottom. Punch holes in the bottom of the pots, and add water to the pan. It will be wicked up to the roots and the hemp plants will have all they need to flourish.
The reservoir is filled with 1 ½ – 3 inches of water and allowed to recede between waterings. When possible, use less solution and water more often, to pull more oxygen to the roots faster over time. If you go away on vacation, simply fill the reservoirs full to the top, and the hemp plants will be watered for 2 weeks at least.
One really great hydroponic medium is Oasis floral foam. Stick lots of holes into it to open it up a little, and start hemp plants/clones in it, moving the cube of foam to rockwool later for larger growth stages. Many prefer floral foam, as it is inert, and adds no PH factors. It’s expensive though, and tends to crumble easily. I’m also not sure it’s very reusable, but it seems to be a popular item at the indoor gardening centers.
Planting can be made easier with hydroponic mediums that require little setup such as rockwool. Rockwool cubes can be reused several times, and are premade to use for hydroponics. Some advantages of rockwool are that it is impossible to over water and there is no transplanting. Just place the plant’s cube on top of a larger rockwool cube and enjoy your extra leisure time.
Some find it best to save money by not buying rockwool and spending time planting in soil or hydroponic mediums such as vermiculite/lava mix. Pearlite is nice, since it is so light. Pearlite can be used instead of or in addition to lava, which must be rinsed and is much heavier.
But rockwool has many advantages that are not appreciated until you spend hours repotting; take a second look. It is not very expensive, and it is reusable. It’s more stable than floral foam, which crunches and powders easily. Rockwool holds 10 times more water than soil, yet is impossible to over-water, because it always retains a high percentage of air. Best of all, there is no transplanting; just place a starter cube into a rockwool grow cube, and when the plant gets very large, place that cube on a rockwool slab. Since rockwool is easily reused over and over, the cost is divided by 3 or 4 crops, and ends up costing no more than vermiculite and lava, which is much more difficult to reclaim, sterilize and reuse (repot) when compared to rockwool. Vermiculite is also very dangerous when dry, and ends up getting in the carpet and into the air when you touch it (even wet), since it drys on the fingers and becomes airborne. For this reason, I do not recommend vermiculite indoors.
Rockwool’s disadvantages are relatively few. It is alkaline PH, so you must use something in the nutrient solution to make it acidic (5.5) so that it brings the rockwool down from 7.7, to 6.5 (vinagar works great.) And it is irritating to the skin when dry, but is not a problem when wet.
To pre-treat rockwool for planting, soak it in a solution of fish emulsion, trace mineral solution and phosphoresic acid (PH Down) for 24 hours, then rinse. This will decrease the need for PH worries later on, as it buffers the rockwool PH to be fairly neutural.
Hydroponics should be used indoors or in greenhouses to speed the growth of hemp plants, so you have more bud in less time. Hydroponics allows you to water the hemp plants daily, and this will speed growth. The main difference between hydroponics and soil growing is that the hydroponic soil or “medium”is made to hold moisture, but drain well, so that there are no over-watering problems associated with continuous watering. Also, hydroponically grown hemp plants do not derive nutrients from soil, but from the solution used to water the hemp plants. Hydroponics reduces worries about mineral buildup in soil, and lack of oxygen to suffocating roots, so leaching is usually not necessary with hydroponics.
Hydroponics allows you to use smaller containers for the same given size plant, when compared to growing in soil. A ¾ gallon pot can easily take a small hydroponically grown plant to maturity. This would be difficult to do in soil, since nutrients are soon used up and roots become cut-off from oxygen as they become root-bound in soil. This problem does not seem to occure nearly as quickly for hydroponic hemp plants, since the roots can still take up nutrients from the constant solution feedings, and the medium passes on oxygen much more redily when the roots become bound in the small container.
Plant food is administered with most waterings, and allows the gardener to strictly control what nutrients are available to the hemp plants at the different stages of plant growth. Watering can be automated to some degree with simple and cheap drip system apparatus, so take advantage of this when possible.
Hydroponics will hasten growing time, so it takes less time to harvest after planting. It makes sense to use simple passive hydroponic techniques when possible. Hydroponics may not be desirable if your growing outdoors, unless you have a greenhouse.
CAUTION: it is necessary keep close watch of hemp plants to be sure they are never allowed to dry too much when growing hydroponically, or roots will be damaged. If you will not be able to tend to the garden every day, be sure the pans are filled enough to last until next time you return, or you can easily lose your crop.
More traditional hydroponic methods (active) are not discussed here. I don’t see any point in making it more diffucult than it needs to be. It is necessary to change the solution every month if your circulating it with a pump, but the reservoir system does away with this problem. Just rinse the medium once a month or so to prevent salts build up by watering from the top of the pot or rockwool cube with pure water. Change plant foods often to avoid deficiencies in the hemp plants. I recommend using 2 different plant foods for each phase of growth, or 4 foods total, to lessen chances of any type of deficiency.
Change the solution more often if you notice the PH is going down quickly (too acid). Due to cationic exchange, solution will tend to get too acid over time, and this will cause nutrients to become unavailable to the hemp plants. Check PH of the medium every time you water to be sure no PH issues are occuring.
Algae will tend to grow on the medium with higher humidities in hydroponics. It will turn a slab of rockwool dark green. To prevent this, use the plastic cover the rockwool came in to cover rockwool slab tops, with holes cut for the hemp plants to stick out of it. It’s easy to cut a packaged slab of rockwool into two pieces, then cut the end of the plastic off each piece. You now have two pieces of slab, each covered with plastic except on the very ends. Now cut 2 or 3 4” square holes in the top to place cubes on it, and place each piece in a clean litter pan. Now your ready to treat the rockwool as described above in anticipation of planting.
If growing in pots, a layer of gravel at the top of a pot may help reduce algae growth, since it will dry very quickly. Algae is merely messy and unsightly; it will not actually cause any complications with the hemp plants.