Aggregates Manager Digital Magazine
Issue link: http://read.dmtmag.com/i/789750
Bill Langer is a consulting research geologist who spent 41 years with the U.S. Geological Survey before starting his own business. He can be reached at Bill_Langer@hotmail.com CARVED IN STONE 44 AGGREGATES MANAGER / March 2017 T hose of you who pay attention to details may have noticed that I have a different puppy with me in the photo at the top of the page. Rosie went to the Rainbow Bridge last June. Our new puppy is named Keiki — Hawaiian for little one. Actually, 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. 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 flood- ed, 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 told Pam that this is not new. A case in point was the gravel-culture installation of the Army Air Forces on Ascension Island in the South Atlantic toward the end of World War II. That tiny volcanic island has a climate characterized by mild tem- peratures and low rainfall; conditions that result in the generation of practically no agricultural soil. The island is so isolated that the large military garrison placed there could only be provided with the 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 to the health of troops. The problem was deemed important enough to justify a determined effort to provide such items as fresh tomatoes, lettuce, pep- pers, radishes, and cucumbers. Because there was no soil on the island to use conventional growing methods, an aggregate cul- ture installation, using a local gravel, was authorized for the soilless production of fresh salad crops. That operation still stands out as an example of the suc- cessful 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. Missouri gravel bed gardening has spread well beyond Missouri. Some places have even created com- munity gravel bed nurseries for area 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. AM Like hydroponic systems, gravel and aggregate cultures have created alternative options for plant growth. Grown in Gravel Aggregate culture allows nurseries to grow plants with minimal damage to the roots when the plants are moved. Image by: David Ryan, Rare Earth Nursery.