How humid need a seedling cannabis indoors?

Humidity and temperature in your marijuana grow room

It is important to know that the amount of absorbable water depends on the temperature. With a temperature of 68°F (20°C), the air can absorb a maximum of 7.2 ml of water. This air has a relative humidity of 100%. When that happens the amount of water vapor is so high that you won't be able to see anything. Air with a temperature of 32°F (0°C) can only absorb about 5 ml of water. This is the reason why the air is a lot drier in the winter than in the summer. I've written an e-book that you can download for free, and that's packed with tips about how to create the perfect climate for your marijuana plant.

Because you constantly ventilate your marijuana grow tent you pull, aside from the heat that the lamps create, also the humid air from the room. Therefore you always have to make sure to keep your grow room moist in order to increase the humidity level. There are several ways to increase the humidity. But first I'll explain why cuttings, seedlings, and growing and blooming marijuana plants all need a different humidity.

What are the best conditions for seedlings?

The best conditions for cannabis seedlings are a bright, warm (21-23ºC) and humid environment with moving air.

Propagators are simple to obtain and provide an ideal start for young cannabis plants. A propagator is a plastic tray with a transparent top which holds in humidity and warm air while allowing seedlings to receive light. This an easy way to maintain a good environment for very young seedlings . However, since the cover prevents normal air movement (which is very important as it encourages young plants to grow strong stems), cannabis seedlings should not be kept in a covered propagator for too long.

Once the young plants produce their second or third pair of serrated leaves, or if they grow taller than about 7 cm with only the first pair, the cover of the propagator should be removed. A small oscillating fan on the lowest setting is a good way to give indoor plants the air movement they need, while outdoor plants can start to receive the natural outdoor air movement when they have reached this size.

How to Control Grow Room Humidity

Irrigate Carefully

If excess humidity is a problem, refining irrigation practices is likely the first step in a solution. In an ideal world all of the nutrient solution would go into the root system with no runoff or excess. Regardless of your growing medium or technique, introducing less moisture into the grow room is the first step in reducing the moisture in the air.

Measuring Humidity

The first step in controlling humidity is measuring it. A hygrometer measures relative humidity fairly accurately, and a more expensive psychrometer gives very accurate information. Knowing your humidity levels is the only way to get a handle on them, so a psychrometer is the best choice for serious growers.

A Humidifier is just like it sounds: a thermostat that controls humidity. When humidity rises, a humidistat kicks on the ventilation. Often, ventilation and the heat from lights are all that's needed to keep humidity down.

Assessing Dehumidification Needs

The amount of dehumidification scales with the size of the grow room and the outside humidity levels. A large volume growing space naturally needs more dehumidification than a smaller one. Humid, coastal locales need more dehumidification too.

You can make sound equipment choices after your grow room's maximum dehumidification needs are nailed down. Once the problem period of excess humidity is identified, you can calculate how much water you need to get rid of and ballpark a dehumidification system based on that. Dehumids are rated in liters per hour or gallons per hour of moisture removal, though their efficiency scales with humidity (i.e., it's easier to collect water from humid air than super dry air).

Heating and Cooling

Larger operations nix those nighttime humidity problems with open ventilation and floor level heating. Because natural gas it so cheap, this can be a practical solution, though it's a wasteful one. Heating in the canopy drops the RH and ventilation blows out the extra moisture.

During the day, air conditioners can serve as dehumidifiers. An air conditioner does this naturally because it cools the air by blowing it over a radiator-type cooling element. The moisture in the air condenses onto that cold surface and is collected in a reservoir. If it's too hot, an AC offers the two-fold benefit of cooling and dehumidification.

Dehumidifiers

A dehumidifier is a lot like an air conditioner. It passes air over a cooling element, condensing the moisture into a reservoir. But then, it passes the same air over a heating element to warm it up again. In an air conditioner, the heat moves to an outside radiator, like the metal fins of the type that mounts in a window. The "dehumid" unit retains the heat in the room while the air conditioner gets rid of it.

Dehumidifiers can be portable, floor units on wheels or large wall-mounted affairs the size of a kitchen refrigerator. They offer some odor mitigation because they remove airborne moisture that carries terpenes and flavonoid molecules (just like air conditioners). But unlike air conditioners, they won't increase heating needs during the dark period. Some dehumids feature filtration as well, further countering the dangers of mold spores.

Desiccant dehumidifiers are a different animal altogether. They use a chemical reaction to collect moisture. The simplest example of a desiccant is the packet of silica beads that comes in a box of new shoes. The beads collect unwanted moisture. The industrial version of a desiccant dehumidifier passes the air over a similar material to collect water. But this special desiccant material, when heated later, lets the moisture falls exhaust away.

Controlling humidity is tough because it changes in relation to temperature. Wily RH values can be crazy-making, but with the right equipment and careful assessment, you can optimize growing conditions and maximize your yields.