Designing an Aquaponic Greenhouse for an Urban Food

In terms of the rock and particle size we should pick a media that is between 8mm and 16mm.If we go
beyond these limits there are some disadvantages (Research, 2010). For example if the media is smaller
then there is not going to be enough air in between particles in the growing bed. If the media larger, we
will have a reduced surface area and planting will become difficult. When we talk about weight we refer
to the density of the media per cubic foot. The pH is the measurement of the acidity or basicity of an
aqueous solution (Covington, Bates, & Durst, 1985).When the most acidic is 1 and the basics is 14,the
neutral pH Is 7.

The most common growing media are shown in the Table 10 below:

Expanded Shale Expanded Clay

(Hydroton)

River Stone Crushed Stone Synthetic

Weight (^) Slightly heavier than
expanded clay
½ the weight of
stone
Heavy Heavy Lightest –
tends to
float
Environmental (^) Mined from a quarry Mined from a
quarry
Mined near local
rivers. Larger
environmental impact
than engineered
quarries
Mined from
quarry or
consists of
crushed river
stone
Made from
petroleum
Origin (^) United States Germany or
China
Local quarry Local quarry China
pH Neutral
(inert)
Yes Yes If the stone has any
limestone, it will
continue to raise the pH
Same as River
Stone
Yes
Easy on the
hands
Yes – even though
the shale has been
crushed, the kiln
process rounds over
all the edges
Yes – though the
spheres tends to
roll away when
dropped!
Yes Typically very
sharp and hard
to dig in with
bare hands
Yes
Cost
per lb.
4.1 $ 4.8 $ 2.8 $ 1.5 $ 5.5 $
Prices amazon.com
Table 10. Growing Media

Figure 31. Growing Bed with Expanded Shale

The best option for our system would be the crushed stone. This kind of growing medium costs less

than the others. It keeps the pH neutral and also is a local quarry. It is very good for growing lettuce,

cucumbers, tomatoes, pak choi, squash, peppers, kale, broccoli, beans, arugula, cabbage, basil,

watercress and chives.