Grown in gravel

Some of you may recall me mentioning our dog Rosie in some of my articles.  Sweet Rosie went to the Rainbow Bridge in June 2016.

Our new puppy is named Keiki – Hawaiian for “little one”. Also, a keiki is an offshoot from an orchid. My wife Pam grows orchids, and this year she planted her Vanda orchids in glass beads.

All plants, including orchids, require water, light, air and essential nutrients to grow, reproduce and perform other critical activities – whether they are grown in soil or not.

In hydroponics (water culture), plants are grown with their roots in water. However, Pam used glass beads, so she was using a technique more akin to gravel culture or aggregate culture.

Sometimes growing plants in aggregates is preferred to the hydroponic method because the aggregate helps to support the roots. The aggregate is held in the same type of tank as is used for a water culture system.

{{image2-a:r-w:200}}The nutrient solution is held in a separate tank and pumped into the aggregate tank to moisten the roots as needed. After the aggregate has been flooded it is drained to provide aeration. Enough water and nutrients cling to the aggregate and roots to supply the plant until the next flooding.

I’ve told Pam that this is not new. A case in point was the gravel culture installation of the US Army Air Forces on Ascension Island in the South Atlantic towards the end of the Second World War. That tiny volcanic island has a climate characterised by mild temperatures and low rainfall – conditions that result in the generation of practically no agricultural soil.

Ascension Island is so isolated the large military garrison placed there could only be provided with essential dietary staples such as grains, meat and milk products. Fruits and vegetables were either canned, dried or dehydrated items. Yuck! This was not only bad for morale, but perhaps even detrimental to the health of the troops.

The problem was deemed important enough to justify a determined effort to provide such items as fresh tomatoes, lettuce, peppers, radishes and cucumbers.

Because there was no soil on Ascension Island to use conventional growing methods, an aggregate culture installation, using a local gravel, was authorised for the soil-less production of fresh salad crops. That operation still stands out as an example of the successful application of aggregate culture in locations devoid of natural soils.

More recently, aggregate culture has found an application in the production of nursery stock.

The Missouri gravel bed (MGB) is a method of handling bare root nursery stock where, during the spring, dormant plants are placed with their bare roots in an irrigated bed of gravel and held for up to a year before planting bare root (in full leaf) in the landscape.

The key to MGB is that root growth in gravel is very fibrous and, unlike with healed-in plants, few roots are damaged when plants are removed from the gravel. Don’t let the name confuse you. MGB gardening has spread well beyond Missouri. Some places have even created community gravel bed nurseries for residents.

Aggregate culture is yet another environmentally friendly application of gravel. And just in case you were wondering, yes, an orchid can make a keiki when it is planted in gravel – or glass beads.

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