Mini-greenhouses for container gardening. Part 2: Plastic bottles (Willem van Cotthem)

In Part 1, the transformation of yogurt pots into a mini-greenhouse was described (see former posting).

In this Part 2, the use of plastic bottles as containers for the production of tree seedlings will be described.  Indeed these bottles also function as “mini-greenhouses” for the roots, because the seedling roots are thus fully protected against drought, limiting the volume of irrigation water in a considerable way (as if the seedlings were grown in a real “greenhouse”).

2008-12 (880) - Avocado seed (Persea americana) put in a yoghurt pot greenhouse to activate germination (see former posting Part 1: Yogurt pots).

2008-12 (917) - Germinating avocado seed in a mini-greenhouse.

2008-12 (921) - Appearance of the young shoot between the 2 cotyledons : the seed is germinating.

2009-01 (953) - At the top of the young shoot little leaves are developing.

2010-02 (533) - A germinating avocado seed can easily be transplanted into a 1,5 liter soda bottle filled with potting soil, twice perforated 2,5 cm (1 inch) above the bottom to assure evacuation of a possible surplus of water. Roots are growing quickly through the potting soil.

2010-02 (100) - Left: An avocado seedling with 3 shoots growing in a soda bottle inversed in the bottom of another bottle. Right: an older seedling grown in a yogurt pot mini-greenhouse.

2010-02 (506) - The same seedling with 3 shoots. Two developed quickly, the third one didn't. This seedling was grown in the upper part of a soda bottle (with the red stop), inverted into the lower part of another bottle, serving as a water tank. To allow water uptake from the tank, the neck of the inverted bottle was perforated just above the red stop.

2010-02 (522) - Many roots have grown towards the red stop of the inverted bottle.

2010-02 (523) - One cuts the plastic without touching the roots so that the top of the bottle can be taken off.

2010-02 (525) - The top of the rootball is set free, while the rest of the rootball is kept moistened inside the bottle, functioning as a protective mini-greenhouse.

2010-02 (526) - The curled roots are unrolled before planting this seedling (with the plastic bottle still surrounding the rootball) in the field, so that this bunch of roots can continue its growth in the soil. Meanwhile the major part of the roots inside the bottle keep the water uptake going.

2010-02 (529) - One can also transplant the inverted bottle (with the top of the rootball set free) into another plastic bottle filled with potting soil. Thus, a longer cilinder of roots can be formed and the seedling grows higher and higher, becoming stronger before transplantation in the field. Before planting in the field, the bottom of the second bottle is cut off (2,5 to 5 cm or 1-2 inches) whereby the top of the rootball is set free to grow into the soil at the bottom of the plantpit. As the seedling is planted, still sitting in the two plastic bottles, all supplementary irrigation water will run towards the bottom of the rootball, thus offering the roots more opportunities to grow quickly into the soil.

With a bit of imagination, a number of variants on growing tree seedlings in plastic bottles can be found.  I am strongly convinced that this technique offers many advantages over the use of polybags in tree nurseries (see also my posting

“BOTTLE REFORESTATION – a new method to combat desertification”

published on January 31st, 2008, on this blog.

It goes without saying that bottle reforestation is an interesting technique for large-scale projects in developing countries as it limits considerably the costs of seedling production and irrigation, both before (in the nursery) and after planting in the field.  It guarantees also a higher survival rate of the planted trees, which again lowers the costs of the project.

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About Willem Van Cotthem

Honorary Professor of Botany, University of Ghent (Belgium). Scientific Consultant for Desertification and Sustainable Development.
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