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Flowering Time Variation in a Red Hill Garden

By Ros Walcott

Aug, 2026

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I have recorded whether a plant is in flower for every plant in our garden each week from 2007-2019. I found the discipline of carefully looking at each plant each week to be incredibly useful in getting to know the plants in our garden, their habits of growth, their reaction to different weather conditions and their general health. I had to stop recording as I became too disabled to visit each plant in the garden each week and I find that I now know less about my plants than I did during the 2007-2019 period. I have tried over the years to find some patterns in the flowering times of the plants in the garden but have concluded that the times are too variable to see statistically significant patterns over such a short period. I applied AI (Claude) to the records from 2007-2019 and am gratified to find that AI cannot discern much of a pattern either. AI developed a table of 167 plants that were recorded over the longest periods (8-11 years). Claude concludes:

1. Longer flowering seasons is the strongest, most credible signal — bloom span lengthened by roughly 3–4 days/year across the panel (borderline significant, p≈0.09), about 5–6 weeks longer over the 11 comparable years.
2. Earlier first bloom is a much weaker signal — average first bloom shifted ~1.4 days/year earlier, but not statistically significant. Oddly, among the individual species with the most reliable long-term records, more trended toward later first bloom (12 species) than earlier (3 species).
3. This pattern (season-lengthening more than season-shifting-earlier) is plausible under actual regional warming — Canberra/ACT has warmed significantly since the late 1990s, with minimum (night) temperatures rising even more than daytime highs, which could extend bloom on both ends rather than just pulling it forward.’

• Claude criticises me for not keeping better records. ‘Logging volume roughly doubled from 2007 (4,808 entries) to 2013–2018 (~10,000+ entries/year), which contaminates naive year-over-year comparisons.’ What AI does not recognise is that our garden is growing over time – in 2007 I recorded 4,808 entries while in 2018 over 10,000 entries per year. This difference represents not my lack of effort in record keeping, but a growing garden with more plants to check.

There are some plants which show statistically significant longer flowering periods.

Acacia rubida   later bloom

Acacia spectablilis   later bloom

Callistemon ‘Edna Walling’s Scarlet Willow’   later bloom

Callistemon ‘Rose Opal’   later bloom

Calocephalus citreus   later bloom

Callistemon ‘Pink Champagne’   later bloom

Eremophila youngi    earlier bloom

Olearia phlogopappa   later bloom

 

 

 

A table of all the data can be seen using this link: Table 1

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