Learning from experience: gardening with bigger grasses in NZ conditions

Late March, so autumn of the first year.

We know quite a bit about many aspects of gardening, particularly shade gardening, but gardening in full sun with big, bold perennials is a whole new ball game here and a steep learning curve. I mentioned a couple of weeks ago that I planned to lift and divide the larger growing grasses that I have used in the new borders.  Of course I am only half way through it. These jobs always take longer than I plan, even factoring in other distractions. But it is interesting to stocktake the performance of these bigger grasses one year on from planting.

Stipa gigantea falls apart into divisions when lifted

Stipa gigantea – the giant feather grass or golden oats. Yes it grows quickly and enthusiastically but is very easy to dig out (not strong-rooted) and pretty much falls apart into divisions when lifted. So it is easy to manage. The flower heads are the feature but while ours bloomed, the sparrows laid waste to them so we did not get the full glory last summer. As far as we can make out, it is sterile so seeding and invasion are not an issue.

It is hard to beat the miscanthus at any time of the year

Miscanthus – I think it is ‘Morning Light’ we have. It required a little more effort to dig it out and an old handsaw and small axe to separate it into pieces but was not particularly difficult. I would not want to leave it too long though, before digging or it would get beyond my physical limits to dig and divide without assistance. It has been a standout. The clumps stand tidily like sentinels and it is brilliant at all stages – the foliage and the plumes. It is the only fully deciduous large grass I am growing and even the pillars of dried foliage have been attractive all winter. It is also close to sterile, setting almost no seed.

Is it Chionocloa rubra? Someone will know but it is a native tussock at least.

Chionocloa rubra – there is a bit of a question mark over the name of this one but a couple of visitors have suggested this identification. A native tussock grass that is performing brilliantly so far in attractive vase-shaped clumps. It is easy enough to dig and divide (more hacking apart with saw and small axe than dividing, to be honest) though I only divided this year to get more plants. It won’t need as much active management as most of the other grasses.

Anemanthele lessoniana is another native grass. It was a little underwhelming in its first year but I am told flowers attractively once established. I started with just three plants so I have divided them after their first year to get more.

The native toetoe (now an austroderia though formerly a cortaderia – our environmentally friendly version of the invasive Argentinian pampas grass) was one I planted a little anxiously, worried about its potential size. I need not have worried. The resident rabbits love it so much that the poor little things have failed to make any headway. I shall have to construct little cages over them if I want them to get any larger. I see we have five different austroderia species native to NZ though which one this is, I am not sure yet.

It appears I failed to photograph the calamgrostris at is peak but it is the third one up on the left in this May scene of late autumn.

Calamagrostis ‘Karl Foerster’. Yes well, this one may be on borrowed time. It is scary. I bought several – I can’t remember if it was 5 or 10 because I divided a couple of clumps mid-season when it was clearly growing strongly (about now, alarm bells should be ringing for experienced gardeners). It is a stock grass for the contemporary perennial gardens we have been looking at, mostly in the UK. Our Canberra daughter also said it was the stand-out grass in her little prairie-style patch. And it was most attractive all summer and autumn. Not so in winter where it has been a messy mix of green and brown. It is deciduous in colder climates but not so here. But that is not the main issue.

Added bucket for scale but I also measured and the root systems reached 45cm across in one year. As a quick aside, my kneeling pad of the day is a piece of rubber carpet underlay cut to size. It doesn’t last that long but it comes from waste destined for landfill anyway and while it lasts, it is good.

The plants I bought came in 2.5 litre pots so larger than a liner but not big. Under one year is all it took for each plant to e x p a n d from about 12 or 14m across to somewhere closer to 45cm across. It took every ounce of my determination and strength to dig out the clumps for they were going deep as well as wide. The root ball is solid and dense and that is when I went to find the axe to chop it apart. I raised my eyebrows and started replanting just a few smaller – much smaller – clumps and these reduced in number the further I went. Most are piled to compost. The clumps I replanted are on trial for one more year but in my bones, I know they are on borrowed time. In our conditions, it is just way too vigorous though I am guessing that in harder conditions with dry summers and cold winters, it may just be deemed a ‘strong’ grower. I don’t know if it seeds but I am not seeing seedlings pop up so far. I would say that it may be quite useful if you want to retain an eroding precipice quickly but as a garden plant, try it before getting too carried away. I think I will decide that its powerful growth outweighs the charm of its flowering plumes.

I haven’t tackled the Elegia capensis yet but it can stay untouched for another year. It is a restio so not one of the grasses, though its growth habit and bamboo-like appearance mean it fits a similar niche in the garden. I know from experience that this is one we can contain if required by cutting around with a sharp spade to reduce its spread.

The smaller grasses can wait but the standout smaller variety so far has been a very dark green form of the Australian lomandra. We have several named forms and I am hoping I will unearth the labels when I lift the clumps again (I hate looking at visible plant labels so I tend to push my labels in so deep that I can’t find them again) and the dark forest green one is by far the pick of the bunch. The rest are a bit… utility, shall I say?

The takeaway lesson from all this is we need to trial plants here. That key plants used widely overseas perform differently in our conditions. It is why we buy garden books that cover design, history, philosophy and contemporary trends but never books written by overseas authors which focus on recommended plants and planting schemes. There is no substitute for local experience.

Postscript: I have finally found a home for the Dutch irises. They always looked a bit crass and coarse in the rockery and other areas where we concentrate on species and dwarf bulbs. But they are perfect with the big grasses, Just the right scale. And they bring in colour now in early September when there is not much else happening in that area.


11 thoughts on “Learning from experience: gardening with bigger grasses in NZ conditions

  1. tonytomeo

    Cortaderia by any other name is still a cortaderia. That would make me nervous.
    The so called sterile Cortaderia selloana is all female, so can not pollinate itself. However, it can sometimes hybridize with the invasive Cortaderia jubata and throw seed!

    1. Abbie Jury Post author

      Totally banned in our part of NZ and probably in most other areas. Which means it MUST be removed. It was widely used for shelter in fields but is way too invasive so our councils went on a total eradication campaign. But our native ones are far better behaved.

  2. Tim Dutton

    A few years ago we needed to move a very large clump of Miscanthus sinensis ‘Variegatus’. That divided just fine with a sharp spade from what I recall (though I may have used the axe as well: I use it to divide toetoe when I’m removing them), but it did seem to set it back a couple of years before all the pieces started to grow lustily again: perhaps we moved it at the wrong time of year?

    Our local toetoe here is Austroderia fulvida and pops up all along the stream banks and other wet parts of the garden with no intervention from us. Due to the very sharp edges to the leaves we try not to have it growing anywhere near a path: I’ve had a few very nasty cuts from them over the years.

    Elegia capensis is a plant we fell in love with when we saw a huge clump at Gordon Collier’s Titoki Point garden many years ago. So we planted one next to a stream. After 4 years we carved a piece off it and planted another next to the pond. Then years later I tried to carve a big piece off that to go by another stream: I snapped the handles of my spade AND shovel in the process! Since then we haven’t tried any more division, but do cut off the outer stems from the clumps every year to contain them a bit. Once they get to the water’s edge they never seem to venture any further, but they have become VERY big plants. We would need a digger to remove them.

    1. Abbie Jury Post author

      I have seen huge plants of the elegia too. I am now eyeing up the ones in my new borders and thinking maybe I need to intervene this year after all, to restrict them a little from the start. I don’t want them too dominant and your example is why I don’t want to leave these plants to get too large before tackling them. It will take me a few more seasons to work out how often I need to get in amongst these plants and which ones I can leave alone for years. I used the yellow Phlomis russeliana in several drifts. In our woodland, it has been a most obliging plant, requiring no ongoing attention but in sunny, open conditions it has grown extremely rapidly. I lifted one block, thinned and replanted it on Friday and I will watch it over summer in comparison to the other two blocks in their second year. I have seen big patches of phlomis that rather lose their charm when they get too congested. If it is going to need to lifting and dividing too often, I may reduce the areas substantially in size. Gardening in full sun and open conditions is a very different proposition to the gentler shade gardening we are accustomed to.

  3. Paul Roper-Gee

    Great stuff. love all these grasses. The Calamagrostis in my ChCh garden has been quick growing but seems to wane after a few years and needs dividing to freshen it up. In a different spot I’m trying another tall grass this year – the NZ form of Deschampsia cespitosa – apparently good in damper soils. I’ve been told the NZ form is different to the D. cespitosa from UK / Europe gardens.

    1. Abbie Jury Post author

      I will have to try the deschampsia – thanks for the recommendation. Grasses are new territory for us. I imagine the calamagrostis would be much better behaved in your climate – drier, colder in winter and hotter in summer. Here it appears too happy and wanting to romp away all year round!

  4. sarahnorling2014

    Thanks for this article, lots of interesting information! What are your thoughts on whether one should cut back or just replant our native grasses when they get overly floppy after a couple of years? (Anemantheles has a tendency to ‘lie down’ after flowering! – am trying to decide what to do with a whole slope of it.) I know cutting back is the practice with e.g. the seasonal Miscanthus Morning Light, but where I’ve tried it, or seen it done, with rejuvenating say Festuca glauca or Chionochloa flavicans…they’ve never really looked the same or regained vigour.

    1. Abbie Jury Post author

      I lack sufficient experience to answer this properly. But I would have thought that the general rule would be cutting back for deciduous grasses and lifting and dividing for evergreen ones?

  5. Tim Dutton

    We’ve used Phlomis russeliana a lot in our garden and it grows pretty well in both the rare sunny spots and in the shadier areas. Like you we don’t have many parts of the garden that could claim to get the fabled ‘all day sun’ that so many plants seem to require according to the gardening books and labels in the garden centres. Mel likes to use te Phlomis as it is such a no-fuss plant and smothers weeds well, has architectural flowers that can be left all winter and is quite easy to remove or thin when the clumps get too big.

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