By Gary Pilarchik (The Rusted Gardener)
These cages can be built in 15 minutes. They will allow you to get your tomatoes into the garden a lot earlier. It works. I use a few every year and I am the first in the area with red tomatoes. Try it!
They act as a wind-break and keep the plant from chilling from winds. They also allow transplants time to get used to the elements without becoming overly-stressed from temperature changes. It makes a mini shelter for them.
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 70's. At night I recommend putting a plate on top, a few hours before the sun sets, so it seals in some heat. It is also important to remove it on sunny days in the morning. The inside of the cages can over heat on full sun days when temperatures get into the 60's.
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 below. The milk jug is filled with water and it will radiate heat outward at night to help maintain a bit more warmth. The day time heat is quickly lost when the sun goes down. Maintaining warmer night temperatures helps prevent the tomato from going dormant so to speak as they do in cold weather.
In the event of a light frost, a hot-house cage with a sealed top will give your tomato a few degrees of frost protection. If you put a milk jug within the wrap, filled with water, it will help out even more!
Plenty of Room and Light
The tomato can grow and get plenty of light. Some cage systems filter out light and they aren't tall enough for the growing tomato plants. Plants outgrow 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. The dark color will absorb heat 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. The goal is early growth!