T-Frames in 4′-Wide Grow-Boxes

Q(s).  I have questions on building the T frames.   I read in one of your earlier posts that when you have a 4′ x 30′ box you place the 4×4 posts on the inside of the box but at the outside edges.  Is that correct?
1. So I would use 8 posts ( four on each side) on each bed?
2. Why have 16″ or half of the T hanging over my grow box into the 3.5′ isle?
3. Why not just use 4 posts placed in the center of the two foot-wide bare spot in the middle of the four foot bed.  The end of the T”s would be 16″ narrower than the bed or 8″ short from the edge on each side.  Would it hurt to have the plants climbing up on an angle from the outside of the box towards the center 8″?

4. I may try the PVC frame over the T-frames to make a greenhouse, in order to extend the growing season.  Is that a good idea?

If I try enclosing the bed is this the reason for placing the T posts on the edges of the box?  Then would I walk down the 2′ isle in the middle of the 4′ bed?

5. How much Pre-Plant Mix do I spread on the inside of the grow-box before I fill it with my mixture of sawdust & sand?  The Gardening Course says 2 lbs. For a 18″ X 30′ bed.  Do I double that and put 4 lbs. Down and not put any gypsum down in the center of the box?  The Grow Box Garden book said 10 pounds of gypsum for a 5′ X 30′ box?

A(s).

1.  Yes, if you are using a 4′-wide box, one big reason for doing so is to maximize your yield in a given space.  You can put two rows of climbing plants in a 4′ bed, which produces as much in 7.5′ width as an 18″ box or bed grows in 10′ of width.  But you should expect to be diligent in your pruning!
 
2.  The T hangs out into the aisle only 12″ or 13″.  This maximizes the sun-exposure for your plants and uses the space most efficiently.
 
3.  Have you ever seen poles placed like an indian tepee, with plants placed around the outside, and trained to climb the tepee?  That’s a similar idea, and it is just the opposite of what you want.  As the plants grow taller and bigger they need more light, but because they are growing toward each other and getting closer and closer together, they get less and less light, thus greatly reducing your yield.  If you place your T-Frames in the middle of the Grow-Box, in order for them to get adequate light, you can only grow 1/2 as many plants in the same space.
 
4.  A PVC frame over the top, such as the one shown in the picture in the Photos section of the MittleiderGardeningGroup@yahoogroups.com, is a very good idea.  You can then use your Grow-Box as a greenhouse in the spring, and it will extend your harvest by several weeks in the fall.  I recommend you take the plastic off, however, in the summer, as it provides some shade, and you want maximum sun (unless you are in the tropics and the temperatures are over 100 degrees fahrenheit).
 
If you are using the Grow-Box as a greenhouse in the early spring, you may want to keep it tightly enclosed and walk down the center, but you should ONLY do it after placing 2″ X 12″ boards the length of the box and supported, so you don’t compress the soil mix.  After your plants are growing, and especially when they have begun to mature, you should not walk down the center of your Grow-Box.  And there will be no room for you to do so, even if you wanted to. 
 
In building the frame and covering it with plastic, you should nail 1″ X 2″ boards to both sides of the plastic at the bottom, on the sides of the Grow-Box.  String ropes under 4 points along the side, and tie loops in the ropes.  Then raise the sides by hooking the loops to a stratgeically-placed nail for maximum light on warm days, and so that you can get into the box to feed and harvest.
 
5.  Since Grow-Box Gardens was written 30 years ago, Dr. Mittleider has determined that 5# of Pre-Plant mix is adequate to be placed on the dirt under a 5′ X 30′ box.  For your 4′-wide box spread 4# of Pre-Plant Mix evenly on the soil under the box.  Of course you will also mix 4# of Pre-Plant,along with 2# of Weekly Feed into the soil mixture as you are filling the box.