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.

The Mittleider Gardening books and Manuals teach all you need to know about this subject, and can be purchased in the Store section, or as digital downloads. 

A digital copy costs 30-40% less, and is available instantly!  I HIGHLY recommend you look here https://www.hightechhomestead.com/Products.htm for the best gardening books available anywhere!  Get one NOW and be gardening TODAY!!

Will Sawdust & Peatmoss Decompose and Disappear?

Q. I was looking for a fertilizer substitute in my country (tropical), and I mentioned I was trying to grow in sand+sawdust mix. The person I talked to mentioned that the sawdust will decompose with time, leaving me with only sand.  I recall reading on your website that the planting mediums do not require to be replaced, but what he said made sense.  What are your experiences with this?

A. Organic materials will, indeed, decompose over time, and become less useful.  They do not disapear altogether, but you will need to supplement them occasionally.  Sawdust is slower to decompose, and thus useful for a longer time than peatmoss.  And perlite – if you can get it – lasts a very long time.  Coconut husks last well, but rice hulls decompose rather fast.

Dr. Mittleider has had the same Grow-Boxes in his backyard garden for over 25 years, and has never replaced the materials, to my knowledge. He has supplemented whenever necessary.  When we say the materials don’t need to be replaced, we mean that so long as there is no disease present, you can continue to use them – supplementing as necessary to keep the box full of soil mix.

Also, in a tropical country, organic materials will decompose faster than they do in colder climates, because not much decomposition happens when materials are frozen.

Containers – Depth, Width, Materials & Drainage

Q. I’m building a large Grow-Box 3′ high 3′ wide 15′ long. We receive 10-12″ of rain per year; we have mostly clay soil. 1) I’d like to promote better drainage and have a 3″ soil augur. Is it better to fill my holes with a gypsum and soil conditioner mix or a gravel and gypsum? 2) I’m hoping to get some County compost to mix with sawdust, sand, gypsum and clay to fill the mankiller in disguise.

A.   A real drainage problem is almost unheard of when using containers, and especially in the dry country you describe.  If you must dig, fill auger holes with course gravel. More likely, you would want to preserve every drop of water for the plants, rather than expediting the drainage. For example, even without raised containers, by making level, raised, ridged beds right in the soil, and having the planting area an inch or so above the aisles, you will normally solve any drainage problem in the low rainfall area in which you live.

Why is your Grow-Box 3 feet deep? If bending over is a problem, I recommend 18″ or at most 2’.  If you like working in a Grow-Box rather than the soil, and low bending isn’t a problem, consider building it 8″ deep.  And for any depth box, fill with peat moss, sawdust, perlite, and sand, in equal amounts by volume.  Any combination is fine, so long as the sand is 25-35% maximum. 

Also, build it 4′ wide, rather than 3′, if you have the space. This size will give you 4 rows of most vegetables, while still allowing plants the light they need, while a 3′-wide box only gives you 2 rows.  Excellent detailed instructions for building Grow-Boxes are in most of the Mittleider gardening books, available at www.growfood.com.

You speak of gypsum as if it was a major ingredient in your soil mix.  In a Grow-Box 8″ deep X 4′ wide X 15′ long, apply just 2# of gypsum evenly over the surface of the soil under the Box before you fill with the planting mix. Then, after filling with the planting mix, apply another 2# evenly over the surface and work it into the soil mix.   After each crop apply 2# to the soil mix and work it in.

Perhaps you only meant to use the gypsum in the holes you propose drilling into the clay soil beneath the Grow-Box.  If that’s the case, I would use sand and gravel in the holes.

The Mittleider Gardening books and Manuals teach all you need to know about this subject, and can be purchased in the Store section, or as digital downloads. 

A digital copy costs 30-40% less, and is available instantly!  I HIGHLY recommend you look here https://www.hightechhomestead.com/Products.htm for the best gardening books available anywhere!  Get one NOW and be gardening TODAY!!