Using Dirt in Grow-Boxes – or Growing Right In the Dirt

To further clarify my last post, most of the time we grow right in the existing dirt, with no soil amendments – no matter how “worn out” or “bad” it is.  Whether you have heavy clay or straight sand, or enything in between, unless the soil is diseased, toxic, or under water you can grow a great garden right in the soil.

However, “If for some reason you really must use Grow-Boxes, because you have no ground, but only a driveway, patio, or rocks, (or if you just want the many benefits offered by Grow-Boxes) then go for it. But DO NOT USE dirt in the Grow-Boxes!”  Following are a few of the many reasons not to use dirt in Grow-Boxes.  I recommend you save this information if you are contemplating that method of growing.

Grow-Boxes are designed to give you an excellent growing environment if you can’t grow in the dirt.  They involve an investment of both time and money, and therefore you should obtain the maximum benefit from their use.  If you put dirt from the garden in Grow-Boxes you defeat some of the reasons for having them in the first place, such as:
1) There are always multiplied thousands of weed seeds lying dormant in the dirt, just waiting for conditions favorable for sprouting.  Putting dirt in a Grow-Box creates that favorable environment, and you will have thousands of weeds, instead of NONE as you should.
2) The likelihood is also high that there will be some bugs and/or disease organisms in the dirt you use.  Put it into your Grow-Box, and suddenly instead of a pristine environment, you have the same problems of fighting bugs and disease as if growing in the soil.
3) By putting dirt in your Grow-Box you have the problems of clay soil, too sandy soil, etc., etc. – again minimizing the benefits of the Grow-Box environment.
4)  The weight of dirt in the box is between 2,000# and 2500# in a single 18″ X 30′ X 8″-high Grow-Box if used exclusively, and much more when saturated with water.  This will put substantial outward pressure on the box, and you will end up re-building your box many times over the years.  On the other hand, using sawdust and sand, I’ve seen Dr. Mittleider’s Grow-Boxes still perfectly usable after 25 years!
PLEASE, don’t try and figure out the best methods by trial and error!  It’s been done for you by the best!  Follow the procedures accurately as outlined, and you will have great success.

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.