Jacaranda (Jacaranda mimosaefolia) is not a great choice for the Perth sand plain.
When they're good, they're wonderful, but after many years of giving them the benefit of the doubt, I have to reluctantly conclude they're just not good often enough *.
The straw that broke the camel's back for me was a recent visit to the Subiaco Square precinct. This area was developed about 15 years ago and Jacaranda was used extensively as the street tree. The results have been somewhat underwhelming as you can see in this picture.
|Sheen St, Subiaco (click to enlarge)|
One tree is of good form and a healthy dark green but metres away is a stunted and misshapen one and beyond that a badly chlorotic (yellow) one. For trees that have been in the ground this long, this isn't a good result.
And it was repeated in every street in the precinct. It's very frustrating but, I have to admit, not uncommon for this species in the alkaline Perth sand.
Seeking to cheer myself up, I headed off to Applecross. For those not familiar, the Perth suburb of Applecross is famous for it's Jacaranda-lined streets. When they're in flower they're dazzling. At this time of year however they've finished flowering so I thought it would be a good time to assess them more objectively - without the lilac-coloured glasses so to speak :)
When you look closely you can see that even in Applecross the Jacarandas are not really doing very well. This was a fairly typical example.
However, when you put a bunch of even average specimens like this together…..
|Jacarandas, Applecross (click to enlarge)|
…you get this. Amazing, huh?
And this I think is the key to this species. If you really do want to use them on the sand plain, plant them close so that the shortcomings of the individual specimens aren't noticed. These ones in Applecross are only 8 - 10m apart. In the streets around Subiaco Square the spacings are too wide leaving the trees looking "naked" and the overall streetscape a bit barren.
If you're a Parks manager on the Perth sand plain and have Jacaranda-lined streets that look disappointing, my suggestion is not to remove them but interplant with more of them. Jam them in so that the individuals get lost in the whole. You just might turn a "lemon" into lemonade :)
* Remember I'm talking about the sand plain here; in the Perth Hills where the soils are heavier and less alkaline, Jacarandas are a different proposition altogether.