Mar 25

Mar 25 On the outer: Yesterday's heroes

Plants we used to think of as good in SA, that aren’t really.

I don’t like to bag plants unnecessarily. Everything in nature has its place, in the wild and the garden. So it’s with reluctance that I use this post to fire some shots.

It’s not that the plants are objectively bad, more that our choice & use of them here in our Mediterranean & semi-arid climates - while OK in the past - now appear misguided in different times with warmer weather, water restrictions, plant breeding breakthroughs and evolutions in our approaches to gardening. Basically that was then & this is now.

All of those on my subjective hit-list below do just fine in places not far from us - even the Adelaide Hills. But they have fallen (or are falling) out of favour in most other parts of SA. So here we go…

Diosma (Coleoneum pulchella)

Golden or otherwise, these are not my favourites & I don't apologise for this. Partnered with volcanic rock or polished pebbles, or maybe a good old expanse of kikuyu & a Hills Hoist, the clipped Diosma bush or hedge was all the rage in mid-suburban landscaping c.1984 & thereabouts.

Diosmas haven't aged well & I'm not entirely sure why. Maybe in 100 years' time they will accrue classic old-world charm. But fashion is not my main issue. It's that they don't appear to be as hardy as first thought. Particularly in the last decade since the Millennium Drought & periods of water restrictions, I've seen an increase in the number of struggling diosmas.

In gardens they do OK but on verges, street plantings and anywhere without supplementary irrigation, they can really go woody & thirsty looking, with occasional branch dieback. Sometimes an entire plant will die. This is normal during extreme weather, but disappointing in a plant long billed as hardy.

I've read that stressed diosmas respond really well to a hard autumn prune. This is encouraging. I've also read several articles & posts saying diosmas have very good heat & drought tolerance in their neck of the woods. So clearly there are other factors at play. But I can't see the reason to persist with a dated plant with problems when these days there are so many superior alternatives of similar size & purpose. There's my two cents' worth anyway.

Ouch! Die-osma! This is a local Golden Diosma in an open sunny spot on poor dry soil but high annual rainfall. Most Diosmas do OK in SA but a good handful also end up like this.

Silver Birch (Betula pendula)

Right through the 70s, 80s and 90s if you walked into a mainstream Adelaide plant nursery and asked about a tree, chances were very high they would have stocked silver birch. It really was a mainstay.

And they populated a lot of front & back yards across the city. They seemed to have a lot of strengths: exquisite foliage, beautiful white papery bark, hardy, fast-growing, no thug-like roots, moderate shade without killing everything underneath them.

Then something happened in the 2000s. A warming climate, the Millennium Drought and eventually strong water restrictions had an effect on the city’s flora. They were inevitably some winners & losers.

One of the biggest losers of all was the silver birch. In an interview with ABC Talkback Gardening in August, Co-owner of Heyne’s Nursery - an institution of Adelaide garden and landscaping - was asked to name the plants he thought had suffered the most since the millennium drought, both in health & sales, and he pinpointed the silver birch as No 1. The amount of woodchipping of birch trees over the coming years, he said, was tragic. Their presence in nurseries is now a shadow of its former self.

Is this sad or a necessary adjustment? Probably both. Silver birches are basically suited for temperate climates and only got by in SA with irrigation & favourable conditions. Once these disappeared many were caught short.

There are still a number of fine specimens around. As a rough guide they are best suited to areas with at least 700mm average annual rainfall and summer average max temps below 28 deg C. This includes the hills and foothill centres like Blackwood & Belair, as well as the Lower Southeast around Mt Gambier.

English Lavender (Lavandula angustifolia)

Emblematic perennial of cottage gardens worldwide, the English lavender often graces magazine covers & B&B flyers due to its photogenic, misty drifts of lilac flowers in summer, especially when presented in clumps or edging.

It deserves its reputation. I do think it has its limits though in hot Mediterranean (Koeppen classification Csa) or semi-arid (Koeppen Bsa) climates.

I have seen a lot of English lavenders go woody, especially in extreme summer weather and extreme cold. In colder climates they are virtually semi-deciduous, and I think this is a drawback. Unlike herbaceous perennials it’s not a good idea to cut them right back to the ground, as they will be set back.

Again, I think the species has a lot going for it in the right locations, but in more extreme settings the Spanish & French lavenders and associated hybrids are so much better, not to mention other silver-foliaged options in say the Teucrium or Rosmarinus genuses.

Difficult .

Kind of like what my English lavender looks like after a cold winter or hot summer

Mexican Orange Blossom (Choisya ternata)

Undoubtedly elegant small shrub that warrants a place in many cottage-style gardens, and needs no further introduction. The fragrant blooms (as its name suggests) are a particular highlight.

As for hardiness I’d call it “3-and-a-half star hardy” – like those 3-and-a-half star motels between Adelaide & Melbourne: solid but with some drawbacks. The species does best in temperate and subtropical climates between say Melbourne and Brisbane – where the summers are not too hot and winters not too cold.

In my neck of the woods I find both frost and dry summers knock it back (with leaf singe and branch dieback being the main respective stress responses). There are still some great specimens both on the Plains & in the Hills, but these are usually the results of careful site selection.”

Evergreen alder (Alnus jorullensis)

The photo below sums everything up. Big, unsubtle, fast-growing and prone to dying off in dry spells.