Soil may be wet and still not be able to supply enough water to roots. This is most often caused by a toxic buildup of (nutrient) salts in the growing medium. When fertilizer salts and salts dissolved in water build up, roots are unable to absorb water and nutrients. Sodium is the worst dissolved solid in water. When just 50 PPM (parts per million) sodium are in the water, roots are able to take in very little water and nutrients. The first outward sign is droopy leaves. Plants wilt as the condition progresses.

The best way to avoid nutrient buildup is to use a fast-draining growing medium and keep allow plenty of drainage. These mediums have adequate air space to make the uptake of nutrients and water faster. Such mediums are difficult to over-water and give the grower much more control.

Roots take up water and nutrients in the presence of oxygen (air). Without enough air available in the root zone, roots cannot function properly. If the level of water is too high, most of the air to be forced out of the growing medium and roots soon rot. Interesting enough, when excess salts build up in the growing medium and roots cannot absorb enough water. Plants will soon show signs of drying out, even though there is more than enough water in the container. If roots are also fried in a hot container under the blazing sun, problems are further compounded.

Some soilless mixes that hold a lot of air drain quickly and retain moisture well include high-quality coco peat or coir, peat moss mixed with vermiculite and rockwool. Often grow stores will have their own special organic soil or soilless mix that works well in local conditions. You can also find great soilless mixes at discount and wholesale nursery stores. If you plan to use a low-quality soil, make sure to mix it with 20-30 percent perlite to improve drainage.

Protect outdoor plants from hot midday sun with shade cloth. Growing under a shade cloth will cut water consumption substantially. Sunlight in the middle of a clear day will yield 50,000 foot-candles. This is much more than cannabis needs to grow big and strong. Shading plants lowers all stress levels and cuts maintenance. Setting up a 30 percent shade cloth would actually increase growth!

Protect containers from hot sunlight. Containers full of soil act as a heat bank. First the outside will be warmed by the sun. Once the soil heats up, it stays warm for hours. White plastic containers dissipate heat quickly. White Styrofoam containers repel light and the easiest to keep cool. Ceramic and concrete pots retain more heat, which keeps the growing medium warmer. Deflect sun-generated heat by shading containers. Set up a board or something to shade the containers from hot sun. This little bit of tender loving care will save you and your plants much misery!

Plants grown in gorilla gardens can often be tied down to stay out of midday sun. Many times it is possible to bend trees or bushes above the marijuana plants to provide shade during the heat of the day.

Beautiful Jack Herer bud in full bloom is the reward for keeping outdoor grow shows cool.

Ducting carries away hot air from this HP sodium lamp. The bends in the ducting and its length reduce air flow efficiency by about half. I believe the room would actually stay cooler if the vent fan was vented directly outdoors rather than attached to the lamp.

This grower keeps mother plants growing with 110 watts of compact fluorescent light. Such lamps are very efficient and create a fraction of the heat generated by metal halides or HP sodium lamps.

These buds look nice, but could have developed about 20-30 percent more weight if the room had been kept cooler.

Protect outdoor plants from wind to reduce transpiration and lower water usage. For example, in the Canary Islands where the wind blows 24 hours a day, growers build stone fences about a meter tall to break the wind. The rocks are stacked so that holes remain in the walls. The holes allow some air to pass through but the majority of wind is stopped. Always build wind blocks so some air passes through. When wind is blocked by a solid wall, it spins over the top of the wall and an even stronger turbulent of wind is forced down on the back side of the wall. The wind breaking wall actually causes more wind to blow on plants!

Indoors, containers tend to heat up less. You can keep them cooler by setting them on cool concrete or tile floors. Also, in general the temperature on the floor is the coolest place in the room. Using white pots indoors will also help keep the growing medium cooler.

The air that comes into the room should be as cool as possible. Always bring it in to the bottom of the room because it will be cooler. One of my friends in California pulled cool air in from under house he was growing in. The air was about 5 degrees C. cooler than the ambient air. He also put the nutrient tank for the hydroponic system near the cool incoming air vent, which helped to cool the nutrient solution. Combining several small tricks like this will really help keep the grow room a few degrees cooler.

Always vent the indoor garden from the highest point in the grow room. Hot air rises and this is the best place to remove it. The ducting between the extraction fan and the air filter should be as straight and short as possible. This will increase the efficiency of the vent fan substantially. In fact, if the air must travel through a vent with a 90-degree corner, the fan looses about half of its efficiency!

Place ballasts outside grow room because they generate heat. Move everything out of the grow room that could generate heat, ballasts, radios, electrical appliances, etc. Some manufacturers offer reflective light hoods with a self-contained vent fan and ducting. The hot air created by the bulb is vented directly out of the room. Although functional, the ducting attached to the light reflectors is cumbersome in a small grow room.

Turn the lights on at night to keep the room cooler during the day. You can turn the vent fan on all day and night. This simple little trick will keep the grow room several degrees cooler.

If possible, move the grow room to the coolest part of the house. Growing in an attic or directly under a roof can create very hot conditions. Basements and rooms with no external walls or walls facing north are the coolest in most homes.

Remember, stay cool!

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