Article 3-3 Optimum Candelbra Method

Optimum Candelabra Methods

The Sea of Green Method was developed by Hydro-Tech in the 1980s, popularized by an American author, and is now widely used in high-tech Holland. The basic idea is to eliminate the vegetative stage and go right into bloom after the cutting is fully rooted. This takes up a lot less floor space, produces less large leaves, shortens the time until harvest, and results in a shorter (easier to illuminate) plant. There is a next generation sea of green method, which is more complicated. The basic idea is to double the bloom length. There are a few issues with these sea of green methods:

  1. larger number of cuttings and plants.
  2. less margin of error, which can result in little useful yield.
  3. size of individual flower clusters is less.

Hydro-Tech has also pioneered a modification of sea of green, called “Candelabra”. The basic idea is to grow the plant to about one foot tall before going into bloom. This takes about two weeks in soil, usually less than that if grown hydroponically or with a soilless medium such as coco-peat. (Increasing the oxygen content by using a more aerated medium improves the growth rate.) If the plant grows another 1′-1.5′ vertically after it is put into the bloom cycle, the plant at harvest is about 2′-2.5′ tall–optimum for the recommended five foot paraboloid reflector. Any taller, and the bottom leaves will not receive enough light.

The era of the 20-1000 watt light grow rooms has come and gone. With today’s technology and methods, a similar yield can be expected with only about 6000 watts of power. There are variations on the recommended candelabra method, depending on the situation and your priorities. Let us consider first a top view schematic of a 20’x20′ basement. The stairwell and a portion of the basement are walled in, to allow for efficient air conditioning and CO2 supplementation.

The veg room is smaller, and is capable of supplying enough one foot tall plants for one five foot paraboloid bloom light every two weeks. This is called the continuous harvest system, in contract to the simultaneous method. With the continuous method, harvest one of the bloom lights every two weeks, and replace with plants which have been in the grow phase for two weeks. If the grow phase were limited to two weeks, and the grow room were always in production, and there were three bloom lights, the bloom phase would have to be completed in six weeks. With a two week grow phase, and the grow room always in production, but an eight week bloom phase, four bloom lights would be needed. If there were less than three bloom lights with a six week bloom cycle, or less than four bloom lights with an eight week bloom cycle–there would be some downtime in the grow room or the grow cycle would have to be more than two weeks or less than one bloom light would have to be harvested at a time.

With the simultaneous method, you would need an amount of lights and space in the grow room equal to that in the bloom room, but the grow room would not be in production most of the time. On the first crop, it maybe more immediately rewarding to use the simultaneous method before converting over to the continuous method. In that case, to avoid getting a large number of metal halide lights for grow, the enhanced spectrum Hortilux hps can be used for both late grow and all of bloom. You can root and grow for a few days with blue spectrum fluorescents (preferably a three tube fixture with electronic ballasts, covering a 10″x20″ area for two flats). Root in two inch cubes for about six days, then when they’ve rooted, insert into a tall three inch or four inch square (rockwool block or pot filled with coco-peat), and grow for another four to six days. If the cutting starts at three inches, and grows another three inches, that will be a six inch tall plant on about day six. Transplant into a one gallon container of rockwool or coco-peat (or a mixture of the two), and grow under a blue spectrum metal halide until it is about 10″ tall (about a week or two). Then simply move the rockwool filled pot from a grow hydro into an empty slot in a bloom hydro; or transplant the coco-peat into a 2.5 gallon container. The coco peat will need a little extra time to recover from transplant shock, then in both cases, grow with the colored-enhanced hps light another two inches (a total of 12″ tall). Using the same Hortilux bulbs, change the light cycle (and fertilizer) to bloom stage.

Lighting: Let us start with the mother plants, the source of cuttings. Two medium size mother plants can be maintained with a horizontal 250 watt metal halide. This hood is small and easy to work with. The reason it is horizontal is that with such a small wattage light, that is the only way to attain sufficient intensity to cover the vertical height of the mother plants.

Twelve to fourteen cuttings are taken, and placed under the dual 40 watt blue spectrum (7500 Kelvin color temperature) for rooting. (Blue spectrum light is the best for rooting.) Slimmer tubes (called t-8) which are electronically ballasted, are more efficient and a better quality light, but are only 32 watts. There is a new three-tube fixture for this type of bulb, which is efficiently shaped and 95% reflective. The cuttings can be placed on a 1’x4′ shelf above the halide light, with overhead fluorescents. They can also be rooted under a blue spectrum metal halide, but that would consume more watts, take more space, and the light distribution wouldn’t be as uniform. Twelve cuttings is all we really need to fill the space under one five foot reflector. The extra two are the margin of error, in case they don’t all root well. They should be rooted in about six days. The cuttings can be grown for about four days in four inch pots filled with coco-peat or tall rockwool squares, under fluorescent light.

The four inch pots or squares can now be placed under the 400 watt blue spectrum (6500 or 10,000 Kelvin) metal halide light(s). The blue spectrum is preferred for this stage, because of its superior rooting ability and the reduction of stem elongation (stretching). There is a new 1000 watt blue spectrum halide, with a color temperature of 10,000 Kelvin, made by Ushio; this is better for rooting and early grow, but less efficient for rapid grow than the less blue bulbs. These blue spectrum 1000 watt metal halide bulbs work well, although they are universal and not super output (position oriented). Eye Lighting makes an excellent 1000 watt super metal halide bulb with enhanced bulb life and spectrum, although not as blue as the Eye Lighting MT400DL/BUD (6500 Kelvin), Sunmaster (7000 Kelvin), or Ushio (10,000 Kelvin). The Eye Lighting super bulb would be less efficient for rooting and early grow phase, but more efficient for rapid grow (probably after day six).

Paraboloid reflectors are preferred, for even distribution of light. Ninety five percent reflective specular reflector material is preferred, because only five percent is converted immediately into heat, and because specular reflects accurately like a mirror. Because of the greater accuracy of specular, the shape of the reflector is more important than the diffused kind. When light is diffused, it is scattered, resulting in multiple bouncing of light inside the reflector, and more light shining back through the bulb.

The best reflector for the 1000 watt bulbs is the five foot paraboloid. It is deep, so it covers the whole bulb, and reflects virtually all the light downward. It is well-shaped; the paraboloid angles reflect a greater amount of light at the edge, so the combined direct and reflected radiation is nearly equal throughout the area of coverage (about 19.5 square feet).

The 4″ paraboloid is the best for the 400 watt bulb, having about 12.5 square feet of coverage, and extending about one inch below the bottom of the bulb. With square six inch pots, you can have about 21 plants per stationary 400 watt light, about twice that number when tracked.

To have sufficient working space, either extend the wall another foot into the bloom room, or install extra doors so you can work on the plants in the growth phase by accessing from the bloom room through open doors.

You can cover the door cracks with black plastic, although if you try to use black plastic entirely for the wall, you may have trouble with the air exchange fans (which almost equalize temperature, humidity, and CO2 levels between the two rooms). Be sure to open this work door only when the lights are on in the bloom room, to prevent a disruption in the flowering hormone production.

The three inch paraboloid has about seven square feet of coverage directly underneath the hood. The bulb protrudes below the bottom of the hood, resulting in more light hitting the walls. Some of this light is reclaimed when it is reflected off the wall, although the angles of the wall are not optimum. This wall reflectance allows for some growth outside the edge of the reflector.

In non-hydroponics, to provide enough plants for a five foot stationary paraboloid bloom light, you’ll ordinarily need either two stationary 400 watt halide lights, or one 400 watt halide with a light track, or a stationary 1000 watt halide light with five foot paraboloid. When tracking the bloom lights, also track the grow lights, or use more grow lights. You can get by with less space in the grow phase by using smaller one gallon pots and transplanting into 2.5 gallon pots for placement under the bloom light, or using hydroponics and just moving the one gallon pot from the grow hydro to the bloom hydro. For non-hydroponics, that will result in transplant shock which will stunt the growth for about one week. It is easier and less traumatic to transplant four inch pots directly into the 2.5 gallon pot; the root ball is smaller and less likely to tear the roots.

The best alternative is to use hydroponics, which minimizes the amount of root space (and medium) required, and thereby simplifies transplanting. This way, you can root cuttings in two inch rockwool cubes, and transplant directly into the one gallon hydro pots for the grow phase, and use the same pots for the bloom phase (just move the pots from the grow hydro into the bloom hydro). All of the devices in the grow room can be run off a single 20 amp 240 volt timer. The lights should be at 240 volt, for greater efficiency, ballast life, and bulb performance. The timer can split the 240 volt into two 120 volt receptacles, to power your 120 volt devices. I recommend for the bloom phase the Eye Lighting (Iwasaki) Hortilux 1000 watt hps. This has 17% more available energy for plant than the standard 1000 watt hps lamp. This is achieved by enhancing the blue spectrum (by 25%) as well as the total output (by 5000 lumens). The retrofit 940 watt hps (which requires a metal halide ballast) has a similar spectrum, but less total output than a standard hps.

The best bloom phase reflector for the candelabra method is the five foot paraboloid, made only by Hydro-Tech. This covers about 19.5 square feet, to a vertical height of 2′-2.5′. The seven foot paraboloid is more efficient, covering about 38.5 square feet, but it is good only to a height of 1′-1.5′. The four foot parabloid is more intense, and could grow plants to about 3′-3.5′, but only covers 12.5′ square feet and is less efficient.

Specular or mirror-like finish is preferred, because of the greater accuracy, and the greater reflectivity possible (95%), resulting in a greater quantity of light applied to the plants. By moving the light on tracks, and having internal air circulation with fans, hot spots are spread out.

One five foot hood on a six foot track covers a 5’x11′ area. Two stationary five foot hoods cover almost the same area. One light on a track is more efficient per watt, but two stationary lights would result in a greater yield. One multi-light timer could power all the blooms lights, tracks, fans, etc. With four 1000 watts lights on a track, a 240 volt 30 amp circuit would be required. With eight 1000 watt stationary lights, a 240 volt 50 amp circuit would be required.

Growing Media: Coco-peat is ground up coconut shells. It is better aerated (has more oxygen) than normal soil or peat moss, although not as aerated as a true hydroponic medium. This means you get some of the benefit of hydroponics, and yet can still handwater (although more often). Place one hand over the top of the four foot pot, and turn upside down, gently tapping. If you’ve grown too long, there will be a root girdle, which should be gently raked to allow root growth into the new medium. Place the root ball into a similar size hole in the 2.5 gallon container of coco-peat.

Rockwool is better aerated and thus grows about 10% faster growth than coco-peat, but requires a hydroponic system for more frequent watering. Simply place the four inch cube on top of another cube, or loose rockwool, or a rockwool slab. Place the drip emitter stake on top of the four inch cube, and irrigate at least every hour, preferably continously, while the lights are on. If you want to use a different hydroponic medium, like expanded clay pellets, root in two inch cubes and transplant directly into the different medium once rooted. The expanded clay pellets work well with the high-flow emitters and tubes, because they drain faster. A high water flow can reduce clogging, especially important with organic fertilizers or supplements.

Construction: Let us say that the steps symbolized in the lower left corner are four foot wide, and extend eight feet into the basement floor space. The first step is to construct a wall using two by fours and plywood. This can go across the whole span of the room, starting with the stairwell. Leave about a 3’x4′ floor space after the last step, and install a door into the vegetative (growth) room, and another door leading into the bloom room. Cut a hole into the wall surrounding the stairwell, and install an air conditioner. You’ll need some two by fours to support the weight of the air conditioner. White paint with an added fungicide can be applied to the plywood. Highly reflective insulating foam sheets can be adhered to the plywood surrounding the stairwell, and the two doors. This will thermally insulate the grow and bloom rooms from the stairwell. Be sure to position the air conditioner with the hot coils in the stairwell, and the cold coils in the bloom room. To almost equalize the temperatures of the grow and bloom rooms, install two axial fans in the wall seperating the two rooms. One fan, near the floor, should blow into the grow room; and the other, near the ceiling, should blow into the bloom room. Be sure the light does not leak from the grow room into the bloom room, by constructing a cardboard light baffle, or use flexible black plastic ducts attached to the axial fans. A couple of doors can be installed to access the plants in the grow room from the bloom room. This minimizes the amount of space required in the grow room, by eliminating the need for aisle walking space. This is especially handy when transplanting the two week old plants from the grow room into the bloom room. Be sure to block light leaks, perhaps with a black plastic sheet, or careful construction.


Temperature: Depending on the genetic variety, most plants start stretching or stem elongating excessively at about 75°F. Set the air conditioner to come on at 75°F. It can go down to 68°F. The AC thermostat may be variable drop, or more likely, it will take the temperature down a set number of degrees, say, three degrees. Allow for about 4000 btu of cooling per 1000 watt light in a basement. If this is not in a basement, in the summertime, double the cooling capacity of the AC. If your AC is not powerful enough, there are a few supplemental cooling procedures:

  1. Your ballasts can be remoted to inside the stairwell, saving about 400 btu per ballast. (By applying a fan (about 65 cfm) to each ballast, the bulb burns brighter and the ballast lasts longer and operates more efficiently.)
  2. A 16″ pedestal mount fan can be applied to the hot coils of the AC, directing the hot air up the stairwell and heating the rest of the house. If the hot coils are thus cooled, the AC operates more efficiently.
  3. You can slowly skim the hot air off the top of the room, using only the small fan in an ozone generator. Mount the ozone machine to the ceiling, and attach a hose or duct to the outflow, venting into the stairwell or chimney. Make sure you only vent the air which passes through the ozone generator, using duct tape to seal leaks. This way minimal CO2 is lost, and vented odor is totally controlled. AC has several advantages over venting. With venting, you are dependent on the outside temperature, because you are bringing in the outside air. If it is too hot outside, you will never get cool enough inside no matter how much you vent. (Blowing smelly air outside may disturb the neighbors, although blowing into the sewer lines would overcome this problem.)

    Venting air to outside the grow room would also vent out the supplemented CO2. If such external venting were minimized by allowing the room temperature to rise to a higher level, the temperature would be above optimum. That would increase stem elongation. The leaves will be thinner and have a higher water content. If the thermostat set-point were not raised above optimum, then when the thermostat shuts off the ventilation, the CO2 would have to be replenished, thus more rapidly exhausting the CO2 gas supply. To prevent the temperature from dropping too much, and the humidity from rising above optimum, operate a dehumidifier, even in the light–off period.

    Humidity. The old style air conditioners would also function as a dehumidifier. The moisture condensing on the cold coils would be collected in a drip pan, and drained off in a tube. The new style air conditioners channel this condensed water to a ferris wheel near the hot coils, which re-evaporates the water. This can be modified by the following steps: remove the AC from it’s housing; apply 100% silicone rubber sealant to form a dam in the channel; drill a hole before the dam; and attach a hose to the hole. The hose can carry the water to a collection bucket, and the water re-used. This way, the AC acts as a dehumidifier. If there are not enough lights to make the AC come on enough to sufficiently dehumidify, operate a dehumidifier in the bloom room. Forty percent is a good target for humidity, unless the bloom period is significantly longer than two months; in which case, 30% would be better to reduce danger of flower mold. At these low humidity levels, the leave pores tend to close to reduce transpiration. High transpiration is beneficial because it will tend to speed plant growth, but only if there is a sufficient water supply. The plant’s genes do not know if there is going to be enough water, so evolution has programmed it to close those pores. This has a side effect of making the absorption of CO2 more difficult.

    Carbon Dioxide supplementation. The sealed environment is better for adding CO2, because high levels can be maintained without losing a lot to external ventilation. There is another method of sealing the growing environment, involving vented hoods. This normally involves a glass cover on the bottom of a horizontal reflector. This glass will filter out approximately 15% of the light, including especially the beneficial UV-B. The horizontal reflectors are used because of their smaller size, thus blocking less natural sunlight in greenhouses. It would also be impractical to have a 5′ or 7′ octagonal glass cover. There are some problems with vented horizontal reflectors in grow rooms:
  4. The light is not distributed uniformly. The greatest intensity is underneath the reflector. The light in the other areas is far dimmer, and is angled diagonally. This can cause the plants to creep horizontally until they reach the high intensity vertical light. This can be overcome with multiple horizontal lights with overlapping fringe areas; however, this would need movable grow benches to avoid wasting light on the aisle space. The plants can be staked to avoid creeping, but the plants at the edge will get less and less light as the reflector is raised above the rapidly growing plants in the center.
  5. The vent hose is too small for multiple reflectors, and the alternative of multiple hoses is cumbersome. If the hose size were increased, that would increase the loss of light, since the hole cannot reflect. Also, the seal is compromised by leaks which are difficult to seal, resulting in the loss of CO2 and smell.
  6. All the vented horizontal reflectors I’ve seen are poorly designed. This results in multiple bouncing of light inside the hood, and light shining through the bulb. This problem is worsened by the diffusion occurring with white or hammered reflective material.
  7. The light which makes it through the glass, and is not absorbed by the plant, is eventually converted into heat. This will increase the water evaporation. So, an AC and dehumidifier would still be needed to maintain a sealed environment.

It is important to remember that with plants, everything works together.

I make the following recommendations assuming all of your important parameters are near optimum. With a relative humidity of 40% (the usual optimum), I recommend maintaining a CO2 level of 3000-3500 ppm. With a relative humdity of 30% (the optimum with the next generation sea of green), I recommend maintaining a CO2 level of 4500-5000 ppm.

If you are able, use a direct reading CO2 sensor/controller. This continuously senses the CO2 level, and maintains the set level. If you can’t afford the approximately $800, get a few of the CO2 diffusion tubes, at $10 a measurement. CO2 is harmful in the light-off period, so curtail emission toward the end of the light-on period, or externally vent when the lights go off.

The application of a special liquid carbon directly to the roots is an excellent adjunct to carbon dioxide gas, as is liquid oxygen in the form of hydrogen peroxide. These are addressed in more detail in another of my articles.