(Revised for 2015)
The plant is better protected but what is equally as important is the soil warms and stay in the 50+ degree range. The warm roots translates into plant growth. Cold roots keep a plant from growing.
Heats During the Day
They will collect the solar heat of the day. A sunny day in the 40's can easily heat the cage into the 80's. At night I recommend putting a plate on top, a few hours before the sun sets, so it stores up some heat. It is also important to remove it on sunny days in the morning. The inside of the cages can over heat on sunny days.
Water Container Heat Storage
I will be doing a new video that adds in a black painted milk jug at the bottom like in the picture. The milk jug is filled with water and it will radiate heat at night to help maintain a bit more warmth. They day time heat is quickly loss when the sun goes down. Maintaining warmer night temperatures helps prevent the tomato from going dormant so to speak.
In the event of a light frost a cage with a sealed top will give your tomato a few degrees of frost protection. The milk jug with it will help out even more!
Plenty of Room and Light
The tomato can grow and get plenty of light. Some early systems filter out light and plants can get spindly or the aren't high enough and plants out grow them before the right temperatures arrive. They grow out of their protection.
Black Plastic (Another trick)
You can also lay a piece of black plastic on the ground with a hole in the middle for the tomato. The cage can go on the plastic and it will warm the soil. A tomato also needs warm roots to start growing or it will sit and wait for the right temperature.
Good Luck with Your Garden,
Gary (The Rusted Garden)
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