By Erik Biksa
Asexual propagation, or the process of taking cuttings or cloning, is one of the more labour intensive practices associated with plant production. Although there is little that can be done in the way of reducing the amount of work that arises from physically removing plant material for the rooting process, you need not spend all of your time hunched over a tray or un-rooted cuttings to ensure successful propagation. This article is intended more for the novice grower, but I am sure some the veteran growers will pick up on a few ideas and concepts. This little project arose when I realized that I would have to be away for a week but needed to root some cuttings.
After some thought provocation, I came to the conclusion that I would need a relatively fool-proof and automated way of keeping the precious cuttings from drying out while taking care not to over-water and rot stems or impede root development. The challenge was to meet the parameters mentioned without any incurring any significant cost while not spending a lot of time in construction, as the project was of a smaller scale and would not likely be repeated. The first place I started was my “junk closet”. The closet contains assorted odds and ends from all things hydroponic. The project started out much like a popular television show where contestants must raid a scrap heap in order to source and construct a device that addresses a specific need. Before I got too far I decided that flood and drain would be the way to go due to it’s relative simplicity and ability to disperse moisture evenly. If the project were of a lager scale and used more frequently with the operator near bye, it would have justified a budget, in which case I might have considered an overhead misting system.
So, out of the closet I gathered:
- 2′ – 3/4″ yellow flex hose
- 1-Little Giant PE-A 80 submersible pump (with a 1/2″ to 3/4″ manifold from a previous project)
- 1- 1 1/4″ Thruhull fitting with gasket
- 1-3/4″ Thruhull fitting with gasket
- 2-3-1/2″ net pots
- small quantity 8-16mm Hydroton (grow rocks)
- 1′ – 1 1/4″ live bait flex hose
- 1-grounded , 24 hr, 120V household appliance timer (30 min intervals)
- clear trash bag
- white (translucent) trash bag
For the growing/propagating tray and reservoir I went out and bought two 37.9L Rubbermaid containers with lids for less than $10. I discovered that one of these bins could easily hold 40 – 1 1/2″ rockwool starter cubes. Jiffy pellets would have stayed too wet with the timer I was using, and I figured the plants would wind up in a hydro system where the peat was not wanted. Ideally, I would liked to have used Oasis Floral Blocks chopped into cubes, or polymerized compost such as “Rapid Rooters” but did not have any kicking around. Oasis and polymerized compost hold significantly more air than rockwool, and would have worked well with the relatively long flood cycle. A note of caution with Oasis: it floats, so the hydroton is critical in anchoring it, otherwise larger Oasis blocks can float around your table like a toy sail-boat with a plant stem for the mast. I would also like to point out the half hour flood cycles are longer than desired, but the unit was built with the materials on hand. That is why it was critical to have the hydroton to keep the rockwool cubes above the moisture level, so they are not submersed by the flood solution, as the hydroton wicks up moisture evenly to the cubes above the water line. By having the cubes wick up the flowing nutrient solution, there is sufficient aeration to accommodate a half hour flood cycle. Also, the depth of hydroton allows the cubes to drain freely and rapidly. Pooled, stagnant water sitting for extended periods beneath the cubes in this scenario could lead to diseases with the warm and humid environment maintained in the sealed unit.
Determine where in your table or container you will install your delivery/drain port and overflow tube. Always use the lowest points if the bottom of the container has raised and lowered areas, to prevent the nutrient solution from pooling after the system drains. Make sure that you allow enough room for the entire diameter of the upper portion of the thruhull fittings. In larger systems, you may consider having multiple overflow tubes to ensure an even depth of nutrient solution and to prevent over-flooding.
Using the thruhull gaskets as a guide, trace the inner circumference onto the area of your container where you intend to install the thruhull fittings. In the case of the Rubbermaid containers, a sharp kitchen knife was used to cut out the holes required. A hole saw is prefered, and is a must if you are dealing with more rigid material such as commercial flood tables.
Cut out the inner circle on the bottoms of the 3 1/2″ net pots. Slide the thruhulls into the holes, so the upper portion of the thruhull fittings are sitting flush with the bottom of the upright net pots. If net pots are unavailable, use a 3″ or 4″ flat-bottomed pot with many, 5/16″ holes drilled into the sides.
You can drain more water out of your container if you put the thruhull gasket to the outside of the container, as the top of the thruhull will sit lower in the tub. However, thruhulls are more susceptible to leaks this way, especially if a hole saw was not used to create the opening. In this case you may decide to apply a small amount of natural silicon sealant or plumbers adhesive on the inside of the container where the thruhull and net cup come into contact with the vessel. Allow a minimum of 24 hours for the adhesive or silicone to cure before subjecting to moisture. Alternatively, large diameter rubber grommets are lower profile, easier to adjust flood depth with, require no adhesives and are typically less expensive.
Set up the table or container on your stand or shelves. Make sure that you have adequate support, as the table or container will get a lot heavier once it is flooded with water. Remember that one litre of water weighs one kilogram! Fill the table or container with hydroton (growrocks) allowing for at least 1/2″ of space between the level of the growing medium and the top of the net pot. This ensures that no material floats over the edge of the net pot into the drain or fill lines. If this occurs while you are away, it can mean disaster. If hydroton is unavailable to you, consider using aquarium gravel, although it is typically slower to drain (and more expensive) than the more commonly used 8-16 mm hydroton. Also ensure that the aquarium gravel is a large enough size that it cannot slip through the openings of the net pots.
Place your reservoir beneath the table or container and determine what length of tubing you need to connect the pump to the flood/drain port, which is in this case, a 3/4″ thruhull fitting. If possible for the overflow port(s), have them drain directly into the reservoir from their height at the bottom of the table or container. As the solution falls into the reservoir, it will draw oxygen (which is critical for healthy cuttings) into the nutrient solution. Alternatively, you can use a drain tube from the overflow(s) to the reservoir. If using a drain tube, it is best that it runs straight up and down and into the depth of solution in the reservoir. If the reservoir is not far beneath the container or table (less than one ft. in this scenario) when flooded and the overflow is draining into the reservoir below (drain end must be immersed), massive oxygen bubbles will rise up the drain tube and cascade into the growing vessel or container. This is one of those things that you will have to see for yourself. It should sound and act like the big air bubbles in drinking water coolers. Also by placing an airstone directly under the drain hose, oxygenated air is filtered through the water and rises into the sealed environment, increasing ambient oxygen levels.
Hydroton carries sediment as a result of handling during shipping that will need to be rinsed from the medium. Carefully fill your reservoir by pouring the water through the container or table and allowing it to drain into the reservoir. This does a great job of removing the sediment from the growing medium. Pump the water containing the sediment from the reservoir. Repeat the process until the water draining back into the reservoir is satisfactorily clear.
If using Rubbermaid containers, you can cut out the inside of one of the lids. This will serve as a gasket for holding down the clear plastic used to maintain warmth and humidity in the container. Cut a clear plastic trash bag so that you have at least an extra six inches going around the perimeter of the tub. Keep both layers of the plastic trash bag intact. The dead airspace between the two layers of the bag offers a surprising amount of insulation and helps to diffuse light. Both of these principles are part of what makes double poly-covered greenhouses so attractive to commercial greenhouse growers.
Turn on the pump (or trip the timer) to commence the flood cycle. Insert a short length (2-3″) of 3/4″ diameter hose into the 1-1/4″ diameter overflow fitting. This allows you to adjust the depth of the nutrient solution in the table or container. Adjust it (by using different lengths of 3/4″ diameter poly hose) so that you see the nutrient solution just beneath the surface of the growing medium. This is the correct depth to allow the rockwool cubes to wick up the oxygenated nutrient solution. Finer mediums usually have more wicking ability, although slower to drain.
Rockwool must be pretreated for 24 hours before setting in plant material such as cuttings. This is due to the fact that rockwool is alkaline in nature and must be treated with a mildly acid solution in order to condition it. The magic trick for any rockwool garden is to maintain the pH of the nutrient solution at 5.5, which usually results in a pH of 6-6.5 in the growing medium. So, prepare your nutrient solution for cuttings. In this case I used General Hydroponics Flora Series in a 1:1:1 ratio with Diamond Nectar to a strength of around 400 ppm (using good quality water). An enzymatic “shielding” product was also added to help combat any potential pathogens. The pH was then adjusted to 5.5 using phosphoric acid. Place the cubes into the container or table and turn on the pump to run for 24 hours. After ensuring that the flood solution is being maintained at the correct depth via the adjustable overflow, cover the table or container with a lid or sheet of plastic so that the cubes can be preconditioned to the correct pH and to ensure that they are fully saturated with oxygenated nutrient solution before the cuttings are set in. This will also help the cubes and nutrient solution to warm up, if the lights are left on. In this case, an aquarium thermometer was inserted through the bag lid, so that temperature could be accurately observed. A digital min/max thermometer with probe would have been ideal. Occasionally check and adjust the pH of the nutrient solution while conditioning the cubes.
After 24 hours have past, you should be ready to take your cuttings. The water in the reservoir may develop a film. Do not be alarmed, this is just a thin film of rockwool fibre washed from the cubes. You may discard this solution, or continue use. In this situation, the inexpensive 24 hour timer was set to come on every 12 hours for 1/2 hour durations in a 24 hour photoperiod provided by flouresecent lighting. As mentioned previously, shorter more frequent flood cycles allow the grower a higher degree of moisture management. Plants do not generally like going from very wet to very dry conditions. They usually prefer a maintained level of even moisture. In an attempt to avoid foliar diseases, the cuttings were not misted. The cuttings were subjected to a 24 hour photoperiod as soon as they were removed from the mother plant. To prevent wilting or sagging which typically occurs within the first 24 hours of new cuttings, a white translucent (allows some light to pass through) kitchen trash bag was used in conjunction with the clear double poly cover to reduce the amount of light and heat in the sealed environment. If possible, remove the white bag after the first 24 to 48 hours.
So, how did it work?
I returned after just under seven days away and was greatly relieved to see live plant material in the home-made propagation chamber. The temperature was at about 85° F (about 27° C) underneath the plastic. The pH in the reservoir and cubes had climbed up to near pH 7 during my absence, although the level of the nutrient solution in the reservoir had hardly gone down. Upon close inspection of the cubes, I could see healthy roots just beginning to form. The foliage of all the cuttings was immaculate (free of blights, algae, etc.) and green. By keeping the chamber sealed with the double plastic sheeting (secured by Rubbermaid lid gasket) the humidity was maintained high enough to prevent any wilting WITHOUT having sprayed or misted the cuttings. I believe that rooting would have been accelerated with bottom heat from a heating mat or heating cables. Although the air temperature inside the chamber seemed to stay near 85°F, the temperature of the medium (hydroton) was actually closer to 75°F.
I personally consider this project a success because even after seven days away, I was rewarded with over 40 healthy, rooted cuttings from a homemade hydroponic system that I built with odds and ends from my junk closet and an investment of about $10 for the two Rubbermaid containers. It just goes to show that with a little planning and ingenuity, growing hydroponically can be reliable, simple, inexpensive, and rewarding.