Vol. I · Field Data — Root Zone
Published Q3 · MMXXVI
Vol. I · Field Data — Root Zone
Published Q3 · MMXXVI
Landscape specifications answer heat with volume: deeper planters, more substrate, cooler roots. Across 51 consecutive days and 88,214 readings we could not find that benefit — a 4.1× difference in substrate moved the number less than two identical planters move from each other. The variable that did show up, three and a half times above that floor, is settled on the drawing, not on the maintenance contract.
What this page is
Measurement window 19 June – 11 August 2026. Local time throughout (UTC+4).
The reasoning behind deep planters is thermal mass: more substrate, slower heating, cooler roots. It is a sensible expectation, and it is why specifications so often answer a hot elevation with a bigger vessel — the most expensive line item on the drawing, and the one that cannot be revised once the deck is built. This record does not support it.
Planters A and C sit on the same irrigation line, in the same sun, on the same schedule, measured across the same 51 days. A holds 61.5 litres of substrate; C holds 15.1. A spent an average of 6.8 hours a day at or above 38 °C. C spent 6.0 — and both crossed the threshold on essentially every day of the record. Before reading anything into that gap, we measured how big a gap this installation produces on its own.
Planters A and B are the same species in the same 61.5-litre vessel on the same line under the same sun. Across 50 shared days their daily hours above threshold differ by a median of 2.0 hours. The 4.1× volume contrast differs by 1.0 — half of that. It is not a small effect. It is an effect this dataset cannot resolve at all, and its direction is not even stable: measured against one of the two identical olives the smaller vessel looks better, against the other it looks worse.
Planter F holds 22.9 litres — a third of A — and sits against a shaded, trellised elevation. Its maximum across the entire summer was 37.5 °C, and it did not cross 38 °C on a single one of 51 days. That contrast is 7.0 hours a day: three and a half times the installation's own spread, with a median daily maximum 7.7 °C apart. One of these two variables shows up far above the noise. The other disappears into it.
A against C isolates volume: same line, same orientation, same schedule, 4.1× the substrate, no benefit. F against A isolates orientation: a third of the substrate, no exceedance in 51 days.
| Planting | Orientation | Soil volume | Max | Median daily min | Hours/day ≥38 °C | Hours/day ≥40 °C | Days with exceedance | |
|---|---|---|---|---|---|---|---|---|
| A. | Oliveline 1 | sun-exposed | 61.5 L | 45.9 °C | 30.5 °C | 6.8 | 3.7 | 50 of 50 |
| B. | Oliveline 1 | sun-exposed | 61.5 L | 48.6 °C | 31.9 °C | 5.4 | 3.7 | 50 of 51 |
| C. | Bougainvillealine 1 | sun-exposed | 15.1 L | 48.7 °C | 30.5 °C | 6.0 | 3.2 | 44 of 51 |
| D. | Ixoraline 1 | sun-exposed | 60.8 L | 44.8 °C | 31.2 °C | 3.2 | 1.0 | 26 of 51 |
| E. | Star jasmineline 2 | shaded / trellised | 21.9 L | 41.2 °C | 31.1 °C | 0.7 | 0.1 | 11 of 51 |
| F. | Ficusline 2 | shaded / trellised | 22.9 L | 37.5 °C | 30.8 °C | 0.0 | 0.0 | 0 of 51 |
A day enters the statistics only when readings cover at least twelve distinct hours of it;
51 days qualify for five planters and 50 for planter A, which was commissioned two days
later. Hours per day are computed from hourly means, matching the way published guidance
states its criterion — as sustained hours, not instantaneous peaks. Minimum readings across
the whole record ranged 28.2–30.3 °C.
What is not in this table. Four further planters on the same installation
were instrumented later in the season and hold only nine to thirteen days of coverage each.
They are excluded from every figure on this page because a fortnight cannot be compared with
a summer — not because of what they show. For the record, the highest single reading anywhere
on the installation came from one of them: 49.4 °C, in a sun-exposed
planter, higher than anything in the table above. Its substrate volume has not yet been
measured, so it is not quoted here.
Mean daily maximum by month. The shaded planters did not hold a fixed advantage — they started the summer far below the sun-exposed line and closed part of the gap as the season deepened. By August the shaded jasmine was averaging a daily maximum of 39.2 °C and had crossed the threshold on 11 days. A shade strategy sized for June is not a shade strategy sized for August.
| Planting | Orientation | June | July | August | Drift | |
|---|---|---|---|---|---|---|
| A. | Olive | sun | 42.4 °C | 42.0 °C | 42.5 °C | +0.1 °C |
| B. | Olive | sun | 42.2 °C | 43.4 °C | 44.9 °C | +2.7 °C |
| C. | Bougainvillea | sun | 38.6 °C | 42.3 °C | 43.7 °C | +5.1 °C |
| D. | Ixora | sun | 40.0 °C | 38.5 °C | 39.8 °C | -0.2 °C |
| E. | Star jasmine | shaded | 35.1 °C | 36.4 °C | 39.2 °C | +4.1 °C |
| F. | Ficus | shaded | 33.6 °C | 34.0 °C | 36.1 °C | +2.5 °C |
Planter D is the exception in both tables and is discussed below rather than removed.
Planters A and B are a replicate pair — same species, same 61.5-litre vessel, same line, same sun, same schedule. Over 50 shared days their hours above threshold differ by a median of 2.0 per day. That is what this installation produces when nothing is different, and it is the yardstick every other comparison on this page is held against. We publish it because a contrast smaller than it is not a finding.
Planters B and F carry the same probe model. B recorded a maximum of 48.6 °C, F a maximum of 37.5 °C — 11.1 °C apart, on the same site, across the same days. A model reading systematically high would have carried the shaded unit up with it. It did not. The readings are the substrate, not the scale.
Volume is varied within the sun-exposed line, where planters range from 15.1 to 61.5 litres — a 4.1× spread — and produce a daily difference of 1.0 hour, half the replicate floor above. The obvious objection to this page, "then specify a deeper planter", is not refuted here so much as left without support: four times the substrate did not move the number far enough to be seen.
Planter D is sun-exposed and holds 60.8 litres, yet records 3.2 hours a day against 5.4–6.8 for the rest of its line. This dataset does not establish why. Probe position within the vessel is the likely explanation, but it is a hypothesis and is not verified here. A record that never shows an inconvenient row is a record worth distrusting.
Extension guidance for container-grown plants states that growers should "strive to always maintain root-zone temperatures below 108º to 113ºF, and chronic, longer exposures below 100ºF to 104ºF" — 42.2–45.0 °C for peaks and 37.8–40.0 °C for sustained exposure (Ingram, Ruter and Martin, HO-119, University of Kentucky Cooperative Extension Service). Our observation threshold of 38 °C sits at the bottom of that band.
The same source frames the criterion the way this page reports it — in duration: "a 104ºF root-zone temperature for 5 to 6 hours per day can impair or damage the physiological processes of most of the plants studied." Under controlled conditions, 42 °C applied six hours a day for twelve weeks killed half of a test population of elm and cut holly root dry weight by 78 per cent (Martin, Ingram and Nell, Arboriculture & Urban Forestry 15(11):272–276, 1989). That is not a heatwave event. It is an ordinary summer, repeated.
One species in these planters appears in the published tables by name. Ixora coccinea carries a predicted critical temperature for direct membrane damage of 132 °F (55.6 °C) on excised roots. Planter D peaked at 44.8 °C — roughly eleven degrees below it. On direct injury, this record says nothing alarming, and we will not imply otherwise.
Not a record heat claim
The same guidance describes ordinary nursery containers in full sun as "consistently exceed[ing] 104ºF for 5 to 10 hours each day."
On this Dubai installation, hours per day above that same 40 °C ran 1.0 to 3.7. By the published yardstick our substrate is milder than a routine production nursery — plausibly because these are large ceramic vessels rather than black plastic.
The point of this page is not that Dubai is exceptional. It is that a well-built, generously specified installation crosses a published chronic threshold on 50 days out of 51 — and that nobody standing on it would know.
Sources are named in full because they are checkable. Our own instrumentation and analysis stack is not named, by policy.
Vessel depth, elevation and shade structure are settled at design stage, before anything is planted, and every planter on a deck inherits that decision for the life of the building. This record cannot find the benefit the volume half is bought for. The half that does show up — orientation and shade structure — is routinely treated as an aesthetic choice rather than a thermal one, and it is the cheaper of the two to get right on paper.
Across all six planters the median daily minimum fell between 30.5 and 31.9 °C — shaded units included. Shade removes the afternoon peak; it does not return the substrate to a resting temperature by dawn. Any irrigation, fertigation or replanting plan built on the assumption of overnight recovery is built on something this record does not show.
For the reference sun-exposed planter the hourly mean stayed at or above 38 °C from 13:00 to 19:00 local time and peaked near 42 °C at 16:00 — remaining above threshold for three to four hours after direct sun had left. Thermal lag moves the maximum into the early evening. An 18:30 irrigation event, chosen precisely to avoid the heat of the day, arrives in roughly 40 °C substrate.