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Why do plants seem to flower so late at Larnach Castle?

Why do plants seem to flower so late at Larnach Castle?


(more technically: Fiona’s theory)

Comments within the garden environs are very possibly, well almost definitely, very different from those that you would expect to hear in the café, reception or even the Lodge or Stables for that matter.

Do not get m me wrong, they are in general from very appreciative customers – they love the place!! Recently there have been a number of comments on how late our flowers are, as in, that they are still blooming late in the season and well, should be dead or over.

So why should this be? Well here we go with ‘Fiona’s scientific guesstimation’. Firstly, the facts.

Fog, we do it well

As most of you will know we have our own unique fogbank here at Larnach Castle; a fog bank that Larnach himself could have bought with him when he immigrated; a family heirloom from the Scottish moors. It can hang over the small promontory on which the castle rests for days on end creating this semi-dark haven in which the plants and us humans must dwell.

We know that many humans can become quite morose in such weather as for the plants, well I have yet to discuss it with them in detail. One thing it will do for them though is slow their path to maturity, especially those that are trying to make their way through all the stages they believe they need to complete each growing season. In this case we are primarily talking about the flowering – see below for more info on this.

Height above sea level

The next small point of difference we have from a lot of other places in our vicinity, is our altitude; our height above sea level. We stand at a nice round 1000ft up here which can be converted to another nice round 300m (well roughly). This not only means that we have to grind our way up here (in our vehicles or, for those that are strong and brave and slightly weird, their own two feet) but that we are also cooler.

Generally, for each 100m climb in elevation you drop 1oC so for us that means we are 3 degrees colder than at sea level, on average. For those that want a little more science, something I read said that when the atmosphere is wet and moist the temperature gradient is much less at only 1°C per 200m climb in altitude thus, not such a range when it’s raining!

Maritime climate

Finally, we have our position close to the ocean, as the crow flies, thus we have a maritime climate. What this means is that our temperatures are not as extreme as one may experience slightly further from the coast, the ocean being a good heat sink.

Just think of the Taieri plains inland from Dunedin or Central Otago; hotter in summer and colder in winter and with greater temperature ranges within a twenty-four-hour period. We do not get as hot (as we all know) but yet we are also not as cold (hard to fathom sometimes) so the theory goes and, I am not sure if that takes into account wind chill.

The guesstimate
My theory runs like this. Plants, unlike us, make their own food (photosynthesis) out of basic ingredients, simply water and carbon dioxide, pretty amazing eh! Do not get me wrong they also require nutrients from the soil to, in essence, create the machinery to allow the reaction to take place.

Anyway, the energy that drives the chemical reaction by which plants can make a sugar out of these molecules is the sun; light to be more precise. In warmer conditions this process is faster and when light intensity is greater. Both of these factors are limiting at our great heights, coastal position …. well, everything said to date.

The overall result of all this is that our plants start later (for most species 3 weeks later than Dunedin), grow slower and finish later cos well, they started later and do not really catch up. Frost normally reminds the last of the late flowers that it is time to wrap up warm and prepare themselves for the long chill ahead.

Metrosideros – This picture of a pohutukawa (or a hybrid) flower was taken on the 26th of April. For most of us this is but weird; they flower in the upper North Island as early as late November and for most December, hence its common name of NZ Christmas tree. In Dunedin, it can be January or for some February, but April! We do have our own climate and as a bonus, the late tourists can get to see what they look like.

This year we had pohutukawas in flower late April; what were they thinking, even for us this was extremely late! I have yet another theory to cover this one, yes, I can come up with them at will (not always a good trait).

This tale begins with a very mild early winter last year and a species of plant that responds to temperature to determine when it will begin growing for the season (normally spring) and, when it will stop to rest for the cooler months ahead (autumn). Last winter many of our Metrosideros spp. (pohutukawa, rata and their various hybrids) mistakenly responded to our ‘warm’ June and early July and decided to set their spring growth off. I did warn them, in no uncertain terms that it was the wrong time of year and to go back to bed.

Like most teenagers (that is sort of their age in plant terms) they completely ignored me and paid for it. The chills arrived with the requisite frosts and all their new growth got burnt to a cinder; silly children. I think that this threw them out for the whole of the following season; they started growing late in spring (having wasted energy trying to grow too early), so began flowering even later than normal and are running scared, so have flowered over a longer period, the flowers being staggered rather than all at once.

The thing to take away from this is; if you have missed the flowering of a particular species in Dunedin come see us up on the hill with our own unique weather and atmosphere.

Dahlia – Some of Keith Hammet’s dahlias do not stop flowering until either: the frosts hit, the wind chill becomes excessive or the nights just become too cool. For us, this can be as late as June.
Delphinium – The delphiniums as they are late April, looking magnificent in the Serpentine Walk.

Qualmark Endorsed Visitor Activity
New Zealand Gardens Trust
Landmarks New Zealand
Tiaki - Care for New Zealand

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