Gardening Innovations Dubai | Creative Garden Ideas

Freestanding planter pots with plants are used extensively for exterior beautification throughout the world. Combinations of live plants and planters are used to great effect either as a matter of choice or as the only practical solution to injecting some live planting into an environment. So far, little attention has been given to the thermal characteristics vis-à-vis ‘heat transfer to the roots’ which this article addresses.

The technological requirements to effect some control over the thermal performance of planters is described, together with the particular benefits that flow from its application.

Background

There are some inherent restrictions with regard to the type of planter and variety of plant that can be used, which in extreme environments can be compounded to make the selection of suitable plant/pot combinations limited.

Plants grown in planters will by the nature of the arrangement, have a limited root volume, unlike plants in the ground which will be able to spread their roots with little to no restrictions. The limited root zone must, therefore, provide the best conditions and environment to provide a secure anchorage for the plant in addition to the most suitable physical environment vis-à-vis water, nutrition etc.

A lesser known and understood variable is the root-ball temperature, a factor that can play a significant role in extreme ‘hot & cold’ climates. The ‘hot’ climate is looked at in the United Arab Emirates, where summer temperatures can reach 50°C in the shade.

The United Arab Emirates has some beautiful landscapes, and much time, effort and money go into their creation and maintenance. The vast predominance of the exterior landscape is “in the ground”, but there are also many free-standing planters and ‘built-in planters’ on display. Few plant varieties thrive in pots in the harsh summer conditions, however, so the choice of plant and pot selection is severely limited.

Thermal Lining

Providing thermal protection to plant roots in planters was an idea conceived and developed by Douglas Bott at Siji Greenhouse. Experiments have been carried out over the last four years to examine the potential benefits of providing thermal lining to planters, with a view to ameliorating the deleterious effects of temperature variations in the root zone.

Initial Experiments

The initial trials were designed simply to see if there were significant benefits to be gained and little attention paid to the flexibility or practicality of the application.

The first planter comprised a simple cubic box assembled with 4”thick polystyrene side walls.

Washingtonia Filifera was the test plant selected, (as a known hardy plant in the UAE environment).

Controls were set up with plants of the same age and stage which were grown alongside the test units in terracotta planters of similar internal volume. Two years later, a comparison established that the plants with thermal protection significantly outperformed the control subjects.

With Thermal lining

Without Thermal lining

Development of the Concept

A search began for a material that would provide thermal protection, whist also fulfilling the desirable characteristics outlined below. It should be:-

Flexible and malleable, to allow conformity to various planter pots (shapes & sizes).
Easy to cut, shape, form and fit.
Thin, to minimize internal volume taken up by insulation (maximize growing media content and minimizing potential planter size/cost).
Light weight.
Clean and easy to work with.
Cost effective.
Inert, non-degradable and long lasting.
And less stressful

An excellent material has been found which is currently undergoing some modifications to improve its application.

Secondary Experiments

The follow-up trials were carried out using this flexible ‘closed pore’ material of ½” thickness, which conformed to the desired characteristics mentioned. It was used to line the internal face of a range of commercially available planters of various types. In each case results were compared with controls in identical, un-insulated planters. The minimum and maximum temperatures were recorded over the peak summer months along with the root-ball temperatures.

After one year the experiment was decommissioned and the root development also examined.

The firstly the graphical results are shown below demonstrating the actual improvements achieved in a typical trial.

Comment

The stronger root system resulting from the inclusion of thermal protection is directly related to the superior development of the visible (above ground) plant element. Over time the accelerated development of the plant ‘with thermal protection’ is likely to become more pronounced when compared to those without. This was the case in the earlier experiment using polystyrene, which after 2 years, showed an even more pronounced difference in top growth than the 1-year-old trial result.

Conclusions

By providing thermal lining, there is potential to expand the scope of the design and specification of exterior plant/pot combinations in exterior landscape in hot climate zones. Plants that were previously borderline cases (considered unsuitable for such applications) may now be possible with the inclusion of thermal protection.

Plant pots also, that have traditionally been avoided due to temperature transfer to the root-ball can now possibly be used with thermal protection.

A further merit is that with improved performance, the incidence of plant replacements may be reduced thus reducing the associated costs.

Such an approach could also be used to insulate ‘built-in’ planters, with similar projected advantages.

Although no experiments have been done to test the effectiveness of thermal insulation in ‘extreme cold’ climates, it is highly likely that an advantage could be gained by ‘cold’ protection using the same product.

For more information, Douglas Bott can be contacted via email: sijigh@emirates.net.ae

Siji Greenhouse

Siji Innovation

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