Tag Archives: Dahlia imperialis

A week of determined gardening

The first half is now all planted

I have not been shilly-shallying around. The first half of the new court garden is planted and I have started on the second half. This is not light work. Mark has rotary hoed and I follow up with raking the area out and getting clods of roots out, as well as squishing the abundance of grass grubs. It has only just occurred to me that had I transferred all those grubs to a jar instead, we should have had enough for a meal of alternative protein. Whether grass grubs are delicious when tossed in garlic butter in a hot pan will likely remain mystery, however. I am not that intrepid.

Starting on the other half – the pressure is on to get it planted before winter sets in 

I describe this as romantic chat between two wheelbarrows (me being a two barrow gardener)

The rush is on because our soils are still warm and temperatures are mild, despite it being late autumn. I am hoping for a few more weeks of grace so the plants can start forming new roots. You would not want to be doing it this late in the season in colder climates or places with heavy soil where the plants would languish in wet, compacting ground. With our excellent drainage and friable, volcanic soils, we have much more leeway.

My plantings are neither complex nor detailed. This is a novel experience here. Most of our garden is highly detailed so going with sweeping plantings of large growing perennials is very different and way easier to put in. Because I am digging and dividing from other areas to get the plant material, it is heavy work but it means I am able to put in sizeable clumps at finished spacings. Had I bought the plants, it would be different. When you are starting with nursery-grown plants in small 10 cm pots, it is really difficult to envisage their mature size and the instinct, always, is to over-plant to get a quicker effect. That of course makes for more work in the future because that over-planting will need thinning sooner, rather than later.

B I G salvias for autumn colour, though I am having to cut back early because of transplanting them

I planted the waves of foundation plants first, using just seven different plant varieties (5 grasses, Astelia chathamica and Elegia capensis), added the blocks of a few additional plants I wanted to use (two black flaxes or phormium, a block of rushes that I have lost the name of already, the giant Albuca nelsonii and a plant of Carmichaelia williamsii which has had a hard life but I hope will survive and thrive) . Finally, I added the flowers. At this stage just the giant inula (likely Inula magnifica), big salvias for autumn flowering, pale foxgloves and Verbascum creticum. I hope I have at last found the right spot for these botanical thugs. The plant selection is fairly typical of the way we garden in that it will end up around 25% native plants integrated with exotics. We have never gone for the deliberate “native garden” but instead select native plants that will work in a mixed situation.

The discards of earlier generations to the left, our plastic generation to the right

There are times when working in the garden here takes on the flavour of an archaeological dig. This used to be a farm and farmers were not exactly renowned for taking their rubbish to the dump. It then became an outlying area of the garden in Mark’s father time, before becoming nursery in our time. I always gather up all the non-biodegradable rubbish as I garden and this haul interested me. Given that our nursery years coincided with the widespread switch to plastics, I was surprised that the volume of modern plastics and synthetics (on the right) was not greater. We must have been tidier than I thought. On the left is the older rubbish. Metal, glass, broken china and some pieces of clay pots, basically. There is quite a lot of broken horticultural glass there. Felix was doing his home propagation back in the days of terracotta pots and wooden seed trays covered with sheets of glass. While the broken glass would have been hazardous in the beginning, time has dulled the edges. Unlike modern plastics, I don’t think there is evidence that glass and shards of pottery enter the food chain and pollute the oceans. In this time when there is growing concern at plastics in the environment, we are relieved to be out of the nursery industry – a business that is now built on extensive use of plastics, some of which may be reused but precious little of it will ever be recycled.

Dahlia imperialis towers some 3 to 4 metres high against the autumn sky

Finally, because I read a brave comment in a southern blog this week boldly declaring, “Even though it’s May, that most dire of months for gardens in the southern hemisphere…” (waving to my friend, Robyn Kilty) , I offer you three flowering plants this week. All are big, rangy, brittle, frost tender and come into their own just as the autumn storms hit. But are they not lovely?

This evergreen tree hydrangea is even larger. Now, I understand classified as a form of H. aspera

And the luculia season has started, bring us sweet scent. Luculia pinceana ‘Fragrant Cloud’.

 

 

 

 

Late Bloomers – the tree dahlias in autumn

Tree dahlia 'Orchid', bred by Keith Hammett

Tree dahlia ‘Orchid’, bred by Keith Hammett

The last clarion call of the autumn flowers here are the tree dahlias, wildly impractical plants to grow but I absolutely love them. There is nothing like their over the top blooms soaring skywards in late autumn.  At least we are lucky in this country that we get clear blue skies with strong light all year round. Otherwise they might be soaring up to the gloom of lower light levels of other climates.

For problem number one is that these are frost tender plants which is not surprising when you consider they originate from Central American areas like Mexico, Columbia and Guatemala. We are not actually frost free in Tikorangi. We have areas of the garden that are so protected now by overhead cover that we can grow the most tender material, but out in the open we still get sufficient frost to require placing tender plants carefully. We may only get three visible frosts each winter, but the air chill on a calm night can get low enough to wreak havoc. And because these tree dahlias don’t start flowering until May and continue into June, they can get hit late in their season.

Left to right: 'Chameleon" , 'Orchid' (both Hammett varieties), D. imperialis and an unnamed Hammett variety.

Left to right: ‘Chameleon” , ‘Orchid’ (both Hammett varieties), D. imperialis and an unnamed Hammett variety.

A hint to the second problem lies in the name – the ‘tree’ part. These are not trees. They have nothing to do with trees. They are a fully deciduous herbaceous perennial but their rapid growth in summer and autumn sees them take on tree-like proportions. It is nothing for them to be 3 metres high, sometimes 4 or even 5 metres. Being dahlias, they are plants for sunny, open positions but they also benefit from some support and shelter from wind which can knock their brittle stems over. They have the hollow stems that are typical of dahlias. Some we grow against sheds or to the side of frames already in place for runner beans and frost protection frames for the bananas and sugar cane.  Some we fence in with heavy duty bamboo cross bars – hitching rails, Mark calls them.

Below ground, they have big, chunky tubers which mean that they are difficult to grow amongst other plants and they take up quite a bit of space for their six weeks of glory.

Not many gardens have both the space and the conditions that suit such particular requirements, along with a tolerance for their scruffy off-times. But if you have and can, they are as easy to grow as your more modest dahlia but with more spectacular results.

New Zealand plant breeder, Keith Hammett, has done a lot of work with dahlias, including tree dahlias. The orange starburst variety which he named ‘Orchid’,  with its twisted petals is more compact than any of the others we grow. It only reaches about 2 metres maximum though that is 2 metres high  and 2 metres wide. We have it by a big mandarin tree whose fruit are ripening as the dahlia blooms. It is a lovely combination.

Dahlia imperialis, my personal favourite

Dahlia imperialis, my personal favourite

My favourite is the simple Dahlia imperialis species and it is the most commonly available plant. When it first comes out, it looks like a clematis from a distance. Yes the blooms are a little floppy and the petals are larger and soft, so easily damaged, but I like the somewhat pendulous form and I think the lilac pink colouring is pretty.

Dahlia imperialis Alba - soaring skywards as winter descends upon us

Dahlia imperialis Alba – soaring skywards as winter descends upon us

Being a species, there are a fair number of different selections of D. imperialis. Our late season double white is Dahlia imperialis alba plena. ‘Alba’ of course means white and ‘plena’ means full and is applied to fully double flower forms. This one towers above a shed and puts on a wonderful display with its shaggy blooms but usually gets cut back by the cold when still in bloom in early June.

While tree dahlias can be grown from tubers in the same way as their smaller dahlia cousins, they are also commonly propagated from cuttings which are easier to handle than their oversized tubers. I admit I have yet to try it – there is a limit to how many tree dahlias we can place here – but the advice is to cut the stems that flowered in autumn, making sure that you have at least two nodes per cutting. Lay it flat because the new roots form from the nodes and cover to a depth of about 10cm. Or you can take spring cuttings from fresh growth. It does not appear to be difficult. I may report back on this because we are taking cuttings this year. We have a newly available position where a large tree fell, opening up what looks to be an ideal space for a tree dahlia or maybe two.

022 - CopyFirst published in the May issue of NZ Gardener and reprinted here with their permission.