Containers on Concrete – Depth of Soil Needed

Q.  I am constructing some 18″ wide Grow-Boxes.  I have run out of dirt area, but have a slab of concrete on which I’m putting 3 boxes.  My question is: If I am going to grow kale,chard, spinach, and greens, how deep does the soil really need to be in the boxes?  Will 4 to 5″ be enough?  Or do I need to fill the box to the top?  For carrots, I’m assuming I’d need to fill it to the top. 

Also, My bell pepper plants survived the summer and are producing again, but the peppers are small.  There are a lot of them on each plant, so should I prune them some?

A.  Do not skimp on the soil mix in your Grow-Boxes.  All root crops obviously need the full 8″, just so the roots can grow to full length, but other plants also need space for their root systems.  You need the 8″ depth for several reasons, including:

1) sufficient room for roots to grow properly,

2)  enough soil mixture to hold sufficient water for the plants,

3)  enough soil mixture to keep from heating up too fast in the hot weather,

4)  matching amounts of fertilizers to soil mixture, so you don’t end up with salinity.

Each of these are important.

Don’t prune the peppers unless you have close to freezing temperatures and you know they won’t mature.

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