f you find that the level of humidity in your room is excessive, steps SHOULD be taken to control it. Overly humid conditions can quickly cause the growth of harmful bacteria and fungus. It can also provide the type of environmental conditions for certain pests to attack your plants.

The easiest method is to install a vent fan on a timer. The timer will regularly turn the vent fan on and exhaust humid air. While this will help considerably it is still a very rough method of control. We prefer more precise humiudty control and therefore use a vent fan powered by an automated controller which will keep the RH level within a set perameter. The controller will sense the RH level in the room and will turn on the vent fan whenever humidity levels reach too high. It will turn the fan off when the RH level has fallen below your chosen setpoint. Here’s an example of a controller we like, - the RHC-1 from Green Air.

In a medium to large scale system, you may find that a vent fan is not sufficient and that a dehumidifier must be employed to solve the problem. Most dehumidifiers you’ll find on the market are not strong enough to handle this sort of situation. They also require regular emptying of the collected water which can be a real pain. We suggest the use of an industrial strength dehumidifier which pumps directly to a local drain. We searched a long time to find one that would suit the needs of a larger grower and are proud to offer the Drizair line of dehumidifiers to you. These are SERIOUS dehumidifiers and are a bit of an investment. However if humidity is a real problem, this solution is well worth it.

It sounds like your orchids are suffering from a dry environment. In Hawaii, orchids grow naturally in the open air because there is so much abundant moisture. This is the environment that your orchids are thirsting for. In summer, the relative humidity should be about 70% during the day and 40% at night, and 50% during the day and 30% at night in winter.

To increase the relative humidity around your plants, place them on a bed of gravel in a water-filled saucer. Place the pot on the gravel, but do not allow the water to touch the pot, to avoid problems with root rot. A humidifier also give excellent results. A humidifier can be run with a timer – with the help of a hygrometer you can experiment to find how long you need to run it for the optimum level of humidity. Another alternative (and one which we prefer ourselves) is to run the humidifier with the help of an RH controller. A third option is the Hermidifer from Green Air which includes a humidistat to automatically control the humidity level AND is can be connected to a water supply for continuous function.

Carbon Dioxide, known as CO2 is a much needed resource for your plants’ development and overall growth. Plants use CO2 in their respiratory cycle, much like we depend on oxygen. Plants can absorb much more CO2 than that which is available at natural atmospheric pressure levels. In most outdoor environments, CO2 is available at 450 parts per million (ppm). Most plants can use anywhere from 1300 to 1600 ppm. This is roughly up to 4X the amount that is available outside. If you give your plants these elevated levels of CO2, you will immediately notice a vast increase in plant growth, development and fruit/production.

A CO2 Injection System runs off of CO2 gas, (much like a soda dispenser) and is a good choice for a small room. The drawbacks to this kind of enrichment system is the need to consistently change CO2 tanks, and the fact that it can often take a long time to enrich a room. It's a great choice for smaller systems. The largest room this system should be used with is 10x10 (and that’s pushing it a little.) We’ve designed a calculator to help you figure out how long to run your emitter system.

We prefer the use of a CO2 Generator for larger rooms. Generators come in different sizes and you can purchase a generator that is optimum for your room size. (You want a generator that is capable of enriching your room in 5 – 10 minutes.) Green Air has created a calculator specifically to help you choose the right size generator.

CO2 generators come in one of two ways. You can choose to run it off of liquid propane tanks or a natural gas line. Liquid propane is fine, but the tanks need to be regularly refilled (this can be a real pain). Natural gas runs off of a natural gas line, which once installed properly, is safe, low maintenance and easy to use.

CO2 emitters do not add any extra heat to a grow room, although CO2 generators do. Depending on the size of generator you choose, you may be adding a considerable amount of heat to you grow room. This combined with grow lights can create a very warm room indeed. The good news is that heat is a necessary catalyst for plants to use the added CO2 and that they prefer much warmer temperatures than they do without CO2 enrichment. Most plants prefer temps of up 90 – 95 degrees with CO2 enrichment. If your room doesn’t heat up this warm you may need to bring in a heater (this can be the case for greenhouses). More often it is the case that the room will get too hot and the use of an air conditioner will employed.

Humidity is the second major issue with CO2 enrichment. CO2 enriched rooms can get extremely wet. This increase in RH is due to the fact that the plants’ metabolic processes are occurring at a more extreme rate and water is flowing up through the roots and out of the leaves quickly. Most plants do not thive in an overly humid environment. Most plants prefer an environment between 55 & 65 RH. The preferred level of humidity fluctuates as the plants move through their season. They will like more humidity in the vegetative stage and less in the fruiting/flowering stage. As the plants grow older, more leaves are generated and more moisture is created. This will become a problem for most growers (although this will change depending on the environment in which you live – if its dry and arid outside, you probably will have few humidity issues)

When the level of humidity gets too high it needs to be removed with either a vent fan or a dehumidifier. The most common problem for most growers is finding the fine balance between exhausting moist air, enriching a room and keeping the temperature at the right level. If this is done incorrectly, CO2 will be exhausted with the air and plants will not get the benefit of the CO2 enrichment. There are many solutions to this conundrum and we will tell you two of our personal favorites. Feel free to modify these examples to fit your needs.

1. If you are using a CO2 emitter system, we suggest use of the Compugas. It is very affordable, easy to use and extremely efficient. It will turn CO2 enrichemnt on and off at predetermined intervals, based on basic information you provide. (Room dimensions, desired ppm, cfh of emitter) It does all the calculations for you and creates a CO2 on/off schedule coupled together with vent fan control for airing out the room. It will turn the CO2 OFF before it turns the vent fan ON and vice versa. It comes standard with a photosenesor which ensures CO2 will be turned off in the dark when plants are unable to use it anyway.

2. For larger situations when a CO2 generator is employed, heat and humidity are even more of an issue. In this type of growing situation, we highly recommend the grower invest in the CDMC Package from Green Air, as well as a Temperature/Humidity Controller. For a detailed explanation of how this works, click on the two product links above or click here to see how they work together.

Your sensors are giving you an ambient environemental reading, which may be very defferent from what the plants themselves are experiencing. In an indoor environment, powerful HID lamps are most likely being employed which give off large amounts of intense heat. Depending on what size lights you have and how close they are to the plants, the plants may be experiencing very hot conditions.

To get a true reading of the conditions your plants are experiencing, we suggest using an indoor/outdoor Thermometer- Hygrometer. The extended sensor allows for placement at the plant tops where temp and humidity reading really matter. If any automated controllers are being used (tempstat, CT-DH-3, RH controller), the set points can be adjusted to compensate for the difference between ambient and plant level conditions. A fan can also be set up to blow across plant tops, thereby removing hot air.

Yes. Plants really appreciate a gentle breeze in a grow room. This breeze prevents stale pockets of moisture and heat from building up, while also providing a gentle and stimulating exercise for plant stalks. Really. A gentle breeze will strengthen plants and help them to grow better.

The jury is still out on this one, but some studies have shown that plants respond favorably to classical and Indian music.

For cooling, we suggest using a vent fan and coupling it together with a Tempstat. When temperatures get too high, the tempstat will turn the vent fan on until the temperature drops below your chosen set point. In most idoor environments, lighting is the major source of heat.

Air Cooling your lights is another possiblen solution. Most horizontal reflectors can be easily converted to air cooling by using a lens, the correct hose fittings & ducting to a 265 CFM vent fan.