GREENWELL’S temperature control role advantage for the critical first two years, from tree planting time at both ends of the scale of temperatures – from high to very high, and down to low and very low temperatures.

Cold temperatures:

It is acknowledged that trees and shrubs need to have as much warm soil time to establish a firm root system base to withstand the coming dormant period.

Northern hemisphere climates can deliver extended extremes of cold to freezing soil temperatures adversely affecting newly establishing root systems. A consequence is the shortening of active root growing time compared to temperate zones.

For example: it was common practise for Floridian citrus growers to mound their sandy soils as high up their stems and certainly above the bud or graft union, to protect their trees from the often severe winter freezes. Observations of the practise indicate the protection given was the result of preventing freezing air movements directly onto the sensitive bark and root surface crown.

A downside to this occurs when there is appreciable clay content in the soil that induces bark rotting over the winter period, and it was an expensive process with the potential to damage shallow root systems.

Selection of cultivars of all desired cultivars that show better cold resistance is an ongoing process. However, physiologically, new plantings do not have the time to develop mature wood above and just below soil surfaces to be fully resistant to this first and even second winter stress period.

Greenwell offers the opportunity to change this micro-environment by filling them with low cost but extremely effective wood chips. Consider the changed physical effect of a cold snap on the developing plant root crown both above and just below soil level. When this plant is watered, the chips soak up a substantial amount of water but aeration is still satisfactory because coarse chips contain a large amount of air space. Plant bark rotting does not occur. The latent heat of fusion occurs maintaining a higher ambient temperature within the Greenwell and still preventing direct air movement within this critical area.

Extremes of heat:

The same process in force for cold temperatures applies at the other end of the spectrum. Using the same coarse chips and keeping them water saturated during extreme heat periods, significantly reduces temperatures below the level that severely damages bark and has a serious effect on the plant’s ability to transfer liquid nutrients up the stem. In addition our concern is such that we apply full strength white paint on tree and shrub butts into their crowns to reflect heat, and it is very effective, adding to the control provided by this system. Adding a Greenwell basin filled with coarse wood chips enhances the process of protection significantly, as they contain a substantive amount of cooling water storage in the chips and in the soil around the sensitive root crown, that we know is also sensitive at extreme temperature ranges.


There is a significant investment of time and money to plant new trees and shrubs. Compared to that cost there is a very small outlay for Greenwell protection with added coarse chips to provide significant protection advantages for extremes in weather events, as well as the proven advantage of a controlled water volume with a desirable soil wetting pattern.

GREENWELL- About the author:

Ian Tolley OAM, was presented with the Order of Australia Medal on behalf of the Queen, by the Government of Australia, for his service to citrus, and the community. He is an internationally recognised Citrus authority, a generalist, and a horticulturist, who has been consulting worldwide for more than 40 years.

Ian is a founding member of the Australian region of the International Plant Propagators Society (IPPS) and acted as both a past Australian President, and also as Australian World President. A founding creator of the International Society of Citrus Nurserymen (ISCN), he holds the position of current Patron of the Society.

He continues to run Masterclasses and Workshops – this past year addressing some 1,000 participants at classes covering the southern regions of South Australia, and Victoria.

This past month he was one of six Fellows asked to present a review of his participation in the Australian Churchill Fellowships, as 50 years ago he was one of the first to receive his Award to study overseas for five months.

He attended the recent 50th Anniversary Convention held in Sydney where over two hundred Fellows met and participated, delivered his address, and participated in TV recordings of the event.

A prolific writer on Horticultural subjects, Ian was the principal writer of ‘Citrus for Everyone’ He also produced a recent update ‘Citrus – A Gardener’s Guide’- as described on his website:

Currently he is working on completion stages of the 450-500 page ‘Common Sense Citrus’, due for release in early 2016.