Small Containers – Figuring Nutrients

Q.  I live on a very small city plot and have almost no spots that get
southern exposure enough that veggies will grow. I have a couple of

1. I would like to put a grow-box in a 20″x90″ site for tomatoes.
This spot is between the house and the sidewalk. Will this work? How
do I figure for nutrients, watering, etc.?

2. The only other place I have is also small; however, it is a cement
slab. Will a grow-box work over cement? Would I have to increase the
heighth of the box to help accommodate for the lack of ground soil?

A.  What you have is a 7 1/2′-long Grow-Bed or box – you can grow in the dirt, or in a container.  It will certainly work, if you have full sunshine for 8+ hours.   You can grow 11 tomato plants in that space – enough to produce about 200# of fresh vine-ripened tomatoes!  Who said you can’t grow a garden in a small space!

If you’re going to grow in the dirt, just dig it thoroughly, eliminating all weeds.  While digging add 8 ounces of Pre-Plant Mix and 4 ounces of Weekly Feed Mix, and mix thoroughly with the soil.

Make 4″-high ridges around the edges by pulling soil from the center of the bed. You should end up with an actual planting area about 12″-wide and 7′ long.

Each time you feed, you should use 4 ounces of Weekly Feed Mix.  Watering should be every day, because the location will be very hot, with the house on one side and a sidewalk on the other.  In the heat of summer you may need to water a second time.  Apply enough water to leave 1″ of water standing in the bed.  If that doesn’t soak in within a couple of hours, then put less in until it does soak in within 2 hours maximum.

You can also build a Grow-Box on your cement slab.  Thousands of MM gardeners have grown this way, with no more height than 8″.  Watering daily is critical, because the sawdust/sand mixture won’t hold water the same way clay soil does.

Fertilize an 18″-wide bed or box with 1 ounce per foot of Pre-Plant Mix – one
time.  Weekly Feed should be applied at the rate of 1/2 ounce per foot of bed or box.

Most things you plant will be on both sides of the bed or box, so you are
actually feeding two rows of plants with that feeding regimen, unless it’s
tomatoes, cucumbers, or other climbing plants, which are only planted one row per 18″-wide bed or box.

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?


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, 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.