Gardeners know that plants grow best in soil that is fertile, well drained, moisture retentive and alive with biological life. When we are not blessed with good soil, adding organic fertilizers can be an effective Band-Aid. But the best long-term solution is to build up the soil and stimulate beneficial soil life by adding organic matter — especially compost and mulch.
Good soil is also important when starting seeds and growing flowers or vegetables in containers. In these growing conditions, plants need soil that’s lighter and more moisture retentive than even the best garden soil. Time and again we have found that the ideal growing medium is a blend of peat moss, vermiculite and perlite.
Here in the US, we have easy access to a number of different peat-based growing mediums and soil conditioners. But in Costa Rica, where my wife Lynette and I garden from January to April, these materials are very expensive and difficult to find. Vermiculite and perlite are made from minerals that are mined in distant locations and their production requires high heat and industrial kilns. Peat moss is made from decayed, compressed sphagnum moss that’s harvested from peat bogs 4000 miles away in northern Canada.
Without access to these excellent soil conditioners, it was hard to imagine how we could start seeds, garden in containers and lighten up the heavy clay soils that are so typical in the part of Costa Rica where we live. Fortunately, nature has provided a local alternative. We are learning that coir – the fibrous waste product from the outer shells of coconuts – is a good substitute for peat moss, vermiculite and perlite. Throughout the tropics, coconuts are harvested for their water, meat and oil.* Now their shells are proving to be valuable as well.
Finding effective soil conditioners is important for the success of our personal garden, but it’s even more important for the success of Mi Tierra, the 5-acre organic fruit and vegetable farm that we operate in Costa Rica. This winter we discovered that 50-pound bags of compressed coir are readily available just a few hours away. Elias Rodriguez, the farm manager of Mi Tierra, screened these blocks of compressed coir to remove lumps and create a uniformly textured growing medium that’s perfect for seed starting, transplanting and growing in containers. Even the lumps are being put to good use. When mixed into the heavy clay soil, they lighten it and improve the tilth. This soil conditioning property is proving especially effective in areas where we transplant crops such as watermelons and squash.
Nature has given coir unique hydrological qualities. Under a microscope, each coir fiber looks like a bundle of straws. When coir absorbs water, it holds the moisture inside, rather than around these fibers. For this reason, wet coir doesn’t really “feel” wet because most of the moisture is held inside the fibers.
All our tests with coir have been encouraging. We have had good results with a coir-based seed starting mix. Our tests using coir as a soil amendment for field crops also look promising. When mixed into the soil, coir lasts longer than compost or leaf mulch, which is an important benefit in tropical climates. Coir’s unique microstructure also makes it more effective than peat moss for maintaining aeration and minimizing water logging.
Our highest hopes for coir are as a growing medium in container gardening. With the farm’s generally poor soils and many challenges to making an adequate supply of compost, plus strong winds, torrential rains, soil diseases, insect pests and troublesome animals (iguanas, monkeys, opossum), we have come to the conclusion that to maintain a consistent output of produce, some crops need to be grown in containers.
In our current container growing trials we are comparing pure coir to the growing mix we’ve been producing ourselves for the past 5 years. We’re also comparing several different organic fertilization protocols, including a slow-release organic fertilizer. We are growing in reused plastic rice bags linked to a drip irrigation system, and are experimenting with preformed cubes of compressed coir that are currently being used in the commercial greenhouse industry. If these tests are successful, the farm could significantly increase the amount of local, organic food it produces. Ideally we can be bringing fruit and vegetables to market 9 to 10 months per year rather than just 3-4 months.
|Elias Rodriquez, farm manager of Mi Tierra, with a bag of screened coir. Bulk coir must be screened before use to remove big lumps.|
|Elias next to watermelons, newly transplanted into heavy clay soil that’s been amended with coir. The cages protect against garobos, which are large omnivorous iguana-like lizards that eat almost everything that isn’t protected.|
My wife Lynette with some of the reused rice bags filled with coir.
|Seedlings started in coir. In the background is a coir brick ready to be hydrated.|
|We are growing eggplants and cucumbers in both coir and a local soil mix. We’re also testing various organic fertilizers and are experimenting with windbreak netting.|
|These tomatoes are growing in pure coir with slow release organic fertilizer and drip irrigation. The surrounding fence protects against iguanas and opossum.|