EXOTIC PLANTS AND/OR UNUSUAL PLANTS at OpdeHaar gardens
What are exotics?
Nothing would be easier than to simply omit discussion of this question and just leave it to intuition. However a brief exploration does turn up some points worthy of reflection. Strictly speaking, as many as 90% of the plants in our European gardens are exotic in the sense that they originated in other parts of the world. Even trees such as the sweet chestnut came over with the Romans. Moreover thousands of plants that were introduced from China and Japan during the 19th and early 20th centuries. For our purposes, my definition of an “exotic” is a plant that looks tropical and /or is evocative of an exotic or tropical location.
Plants with large or elaborate leaves come to mind e.g. gunnera, musa species (bananas), tetrapanax (rice plant), fatsia, geranium yeoi and melianthus. Canna, colocasia or coleus also evoke the exotic. Finally, plants such as the palm, Trachycarpus fortunei, prickly pear cacti (opuntia species), various yucca and agave all have undeniable associations with faraway places.
I think you get the picture and I hope that it is clear. An exotic plant is not necessarily tender in our winters but clearly many are. At “Op de Haar”, our general rule is that our exotics must be hardy enough to survive out in the ground with, where necessary, some winter protection. This may be in the form of mulch or wind protection but must not be too labour intensive. Additionally, the plants need to grow attractively each year as opposed to just surviving. There is nothing worse than a plant which is obviously totally unhappy and it will certainly attract the most comment.
All photos were taken in our garden.
Click on the photos for a larger image and a slideshow.
The role of exotic plants in the garden
One of the undoubted pleasures of a varied garden like “OpdeHaar” is that there is something to see in each season of the year. However, when the floral contributions of many perennials start to falter in early August and the autumn flowerers such as aster and dahlias are also visibly running out of steam, there is indeed scope for a “wow factor” to fill the gap until the first frosts. This is exactly when many exotics come into their own.
Many of these plants do not really get going much before mid-June. So a degree of planning is called for when incorporating them into planting schemes. For example, a space left by spring bulbs can be subsequently filled by something like a hardy ginger such as Hedychium Tara.
Exotics in our tropical border
The Tropical border is home for many of our “exotics”. This area is very well sheltered and receives full sun from around 10.30 onwards. The soil is well drained and it can get unpleasantly hot (40ºC plus) on a summer’s day. Furthermore the temperature may even surprise you in the middle of winter. Current planting started in 2004. However we are still moving some plants that are twice as big as they should be and juggling with new plantings in order to get a satisfactory aesthetic balance.
As recently as 5 years ago, many plants now appearing from the colder areas of New Zealand, South America, Nepal and China had simply not been trialed in The Netherlands. In addition, it is now recognised that some plants from desert areas have a tolerance of formidably low temperatures. The question is how they will cope with our winters, if, for example, they are kept dry, as in the desert. There is only one way to find out – try them. This is truly experimental and is an aspect of gardening that has a strong personal appeal to an ex-research chemist.
Explosion of new plants
If a Victorian gardener was to see how modern nurseries offered ranges of camellia and bamboo for planting outside in our gardens he would surely shake his head in disbelief. Over the past 15 years we have planted numerous Fatsia japonica around our gardens where they grow quite happily. However they still attract questions as to how we manage to keep “houseplants” outside! Another example is our rather large hardy palm tree, Trachycarpus fortunei, which has grown happily in a corner of the rose garden for more than 15 years. By way of illustration, Major Lawrence Johnston planted them at Hidcote Manor in the Cotswolds, UK, on an exposed hilltop in the 1930’s.
The point that I am trying to make is very simply that there are relatively large numbers of plants with exotic or subtropical connections that can be grown outside in The Netherlands. Getting hold of them is becoming increasingly easy thanks to specialist nurseries and seed companies (see websites). They offer the gardener something different albeit sometimes in exchange for a little extra work in the form of winter protection. We are certainly not experts in exotics, but regard them simply as extensions of what is currently available at most garden centres. Hopefully these notes will tempt you to try an exotic plant or two in your garden.
Just to show you how we protect our more tender plants in winter here is a photo of the overfull greenhouse (after all I said!).
Konjac is a member of the edible Amorphophallus family and is cultivated in Japan, China and S.E.Asia. There is no shortage of background information on the Internet.
It is not winter-hard in Northern Europe. However it goes conveniently dormant in the winter months when the tubers can be stored dry in a cool, dark place; if space is at a premium, they need not be in pots. In early summer, tubers send up a single attractively patterned stem with a bush of leaves at the extremity. Mature tubers (about 3 years or more) send up a characteristic “flower” from around March if temperatures are at least 20 deg C. They will do this from a tuber which you have not potted up as a fairly blunt prompt to get your act together! The photographs illustrate what one can expect. After what I said about a single leaf stalk per tuber, it will be apparent that numerous off-sets are produced as tubers grow and these are easily potted on.
Amorphophallus Konjac is fairly easy to grow and responds gratifyingly to heavy organic feeding. In Japan, planting in holes enriched with manure is widely practised. I have used slow-release fertiliser in the pots with acceptable results, as the photographs show. Konjac needs to be kept moist throughout the growing season, in light shade and not exposed to the full summer sun. It can be allowed to dry off once the leaves start to yellow at the end of summer. Some people advise giving a final potash-rich feed at this stage.
“Herb Robert”is well known in northern Europe where it generally has the status of an attractive weed. We never saw it in our woodland until more than 20 years ago when Joyce found a small seedling on a path during a walk on Madeira and decided she would grow what we had decided was a seedling Geranium maderense. It turned out that we had not saved the largest member of the Herb Robert family but its baby brother which is perfectly winter-hardy here in the Netherlands. It now appears literally everywhere around our property. I find it a decorative little thing and only move it when it is definitely in the wrong place; this is very easy to do and is not a chore.
We have subsequently grown G.maderense in pots – seed is widely available and germinates readily. This giant Herb Robert is a short-lived plant which is usually treated as a biennial but is not a hardy plant outdoors in The Netherlands. It is the largest Geranium and I have to confess that I find it the most attractive. Ironically, if you travel south east from Madeira to The Canary Islands, just off the coast from the Sahara desert, you arrive at the home of another Herb Robert in the form of Geranium palmatum. This is arguably rather less spectacular than its northern cousin but is reportedly more winter-hardy back home in NL. For readers wanting to delve into more practical background detail on these two geraniums, there is a really informative blog by Dan Cooper who gardens in Kent .
In a garden such as Op de Haar cared for by a couple who aren’t getting any younger, any plant which demands the care of a container year-round has to be exceptionally special to be added to the collection. A couple of years ago, I could hardly believe my eyes when I saw a tray of what looked like G.maderense at our local nursery run by a real plantsman couple, Hans and Miranda Kramer , which on closer inspection was named as Geranium yeoi which the literature reveals to be a re-naming of Geranium rubescens . The photo and text taken from the Hessenhof website are both informative and revealing:
Hans says: “According to the literature, this Madeiran native is biennial but this is definitely not our experience. Moreover, although it is a relative of our Herb Robert, the flowers are five times larger and fluorescent magenta-pink and we have recorded a size of 4.5 cm. The plant itself is highly reminiscent of Geranium maderense” . Hans goes on to speculate that maybe the plant he has is maybe a hybrid with something like G.canariense ( now G.reuteri) with a far higher degree of winter-hardiness than previously realised. The photo below of plants at the end of the first growing season in our garden gives an idea of the size and the foliage :
Whatever this mystery Herb Robert is, it does provide seed because I discovered seedlings in pots under the greenhouse staging after a plant I had there flowered. It should be noted that Hans has a VERY free-draining soil at his nursery which invariably helps plants of marginal hardiness through the winter. My first plant which over-wintered in 2017-18 seemed to want to continue growing and flowering through what was a very mild winter. There was a sudden very cold period at the end of March (“Beast from the East” as the media christened it) and my plant rotted off at the base. This prompts me to remind people growing both G.yeoi and maderense that their lower leaf stems (petioles) get very wooden and seem to dry off. The last thing you should do is try to neaten up plants by trimming these stems off because they support the plant which has a rather weak root structure and stop it flopping over on its side. (G.palmatum is not reliant on this ancilliary petiole support mechanism)
The winter of 2018/2019 was neither cold nor wet here in the central Netherlands but the gardener in me triumphed over the scientist and I put bubble plastic covers over my large geraniums until the start of April. As I write these lines on 1 June 2019, both G.palmatum and G.yeoi have been in flower for 3 days or so and both have very similar flowering stem structures with the significant difference in plant size being the only visual difference.
The larger geranium variety (G. yeoi) lacks any hint of red pigmentation in its stems which adds weight to Hans Kramer’s suggestion that it isn’t actually G.yeoi/rubescens. While its size and the support mechanism of resting on lower stems are shared with G.maderense, this is where similarities end. This line of thought prompts one to wonder if indeed it is a hybrid involving G.maderense with one or more other exotic Herb Roberts such as G.palmatum and even G.yeoi/rubescens itself. Besides continuing to monitor the perennial nature of my plant, I need to cultivate the genuine Geranium yeoi so I can make more informed observations. The saga continues!
Towards the end of June 1919, I removed the flower stems from four geraniums I had planted early in 2018 and harvested a large quantity of seed and immediately surface sowed a portion in a seed tray. Germination was quick within a couple of weeks and as good as 100%. Seedlings developed rapidly and were soon ready for potting on and by September were large enough to be planted out in a range of locations around the woodland garden. The idea is to see how they respond to a range of varying shade and moisture levels besides monitoring their hardiness and longevity. Importantly, I should note that as far as I can see, the plants are identical to their parents.
The 4 mother plants came through the very mild 2019/2020 winter without any protection and have become almost sub-shrubs of about 1 metre height and circumference. In fact, this size really does need allowing for when positioning a new plant . These established plants are flowering more abundantly than ever as I write in mid-June. Their progeny around the wood are clearly putting their efforts into growth and have fewer flowers but seem very tolerant of shade and, indeed, the dry conditions we had in the Spring.
Melianthus major takes us into the realm of fancy leaves and is a long established favourite in milder gardens. The late Christopher Lloyd of Great Dixter (UK) fame often said it was his favourite foliage plant in the border. Ironically it is a blessing that it is cut to the ground by frosts each year because it is the new foliage that is most beautiful. If you doubt this, just look at the woody stems topped by feathery growths that you can see in its homeland of S. Africa or in locations such as Madeira. Indeed, where frost does not cut it back, pruning sheers should do. One sacrifices rather insignificant flowers but so what.
Melianthus major is very easy from seed and increasingly one sees plants for sale in garden centres (2010). So it isn’t too great a disaster if one loses them in the winter. However, one can get a much better show from a well-developed rootstock. For this reason it isn’t a bad idea to try and over-winter plants.
Here in the central Netherlands I’ve had mixed success when I’ve kept plants in the ground (dry and protected). Very often I find the rootstock has partially rotted. In recent years I have been cutting the plants back just as the first frosts are predicted and potting the roots up for storage under the greenhouse staging until shoots start to develop in early spring. The plants can go back out once Jack Frost has departed. For what can be a sizeable shrub (1.5 x 1m) by year-end the root system is pretty compact. So one isn’t talking in terms of massive plant pots and a lot of storage space. The procedure is certainly no more trouble than lifting dahlia tubers. If you ensure a fertile soil and plenty of moisture, you can have very robust bushes by August which are mid to rear-of-border subjects in this tropical border.
This hardy member of the Aralia or Ivy family (Araliaceae) occurs naturally in the (very) moist forests of British Columbia where we took this photo in September 2017. It has many of the visual characteristics of its sub-tropical cousin, Tetrapanax papyrifer, albeit on a smaller scale. In its native habitat it can form large groves as suckers form from its spreading rootstock. Wikipedia contains a good review for Oplopanax: https://en.wikipedia.org/wiki/Devil%27s_club.
It is surprisingly difficult to find in The Netherlands although searching on Google indicates that this may be because no nursery bothers to cultivate it. My plant came from a batch imported from Canada by the Firm Esveld here in Boskoop where the late owner said that he generally expected about 80% of the plants to fail. This conversation came about because the plants that year all looked to be thriving so I bought one! This was about 10 years ago and my plant has SLOWLY formed a sturdy stem just over a meter high but with no signs of spreading as yet. Maybe it is just plain difficult to cultivate commercially and with its slow growth, the quicker wow factor of something like Tetrapanax just eclipses it as well. Totally illogically, I have grown quite fond of my plant which does attract a lot of spontaneous comments from visitors in our woodland. This all said, it is listed by Crug Farm.
As is the case with many plants, the American Oplopanax has a very similar Asian counterpart – Oplopanax japonicus . Although this is also listed by Crug Farm , I have never seen it growing. To judge from the literature, the Japanese variant will form hybrids with O.horridus. Crug Farm make the salient cultivation statement that both Oplopanax plants are intolerant of high temperatures which provides an additional reason for why plants are so difficult to locate in the nursery trade, particularly in central and southern Europe.
In the perennial borders our only hardy citrus plant, Poncirus trifoliata (Japanese bitter orange) is loaded with oranges as I write on this frosty November morning. I notice that Hans Prins, Kwekerij de Groene Prins has ambitions to start a mini-citrus plantation an hour to the north of here but I don’t think we will go to these lengths.
Poncirus trifoliata carries remarkable spines on its stems and is, I have read, used as a hedge to keep out unwelcome intruders. Take care not to plant it next to a path where it could catch an arm or a leg. In spring, it carries beautifully scented white flowers that ripen into tomato-sized yellow fruits in the autumn. It came from N. china to Europe in 1850 and does best in full sun and is perfectly hardy without winter protection.
Tetrapanax name and family
Tetrapanax is a member of the family Araliaceae along with Fatsia, Aralia, Hedera, Schefflera and Oplopanax. The taxonomy in the group remains labile and Tetrapanax papyrifer was previously called “Fatsia Papyrifera”. One still rarely comes across mixed nomenclature such as Tetrapanax papyfera and even variants such as papyriferum or papyriferus. Tony Avent of Plants Delight Nursery in USA has given an insight into the origins of giants such as “Steroidal Giant”. He also has good photographs of both Tetrapanax papyrifer and “Steroidal Giant” for comparison in his catalogue. (Use the search function on his site or click here.)
My “Steroidal Giant”
My “Steroidal Giant” was planted out in a suitably moist and sheltered spot in full sun early in 2006. It sat and didn’t do anything really spectacular right through until August, which was one of the wettest on record in the Netherlands. This prompted the steroids to kick in and it developed a thick stem about 1m high by the time it dropped its leaves in early November. In 2007 it proceeded to dwarf a Gunnera manicata and threatened to mask out Musa sikkimensis with leaves that could truly be described as awesome! In fact, spectacularly large Sauromatum nubicum plants almost looked like incidental decoration in its shade. The lesson is obviously that it needs adequate space. 4m2 would have been just enough in my case.
Finally in the spring of 2008 I decided to shift the thing. I took out the trunk with what I assumed was a very generous portion of root. It never even made an attempt to make growth but, like Monty Python’s Norwegian blue parrot, the bare stem stood bravely erect until I finally dug the corpse out. Meanwhile, curiously familiar leaves eventually developed into small tetrapanaxes over several square meters of our exotics border. Interestingly, prior to this there hadn’t been a sign of any suckering from the roots. Throughout 2008, I have been potting up these plants and, as I write (November 2008), they are growing happily in the greenhouse.
The Tetrapanax formed rather thick roots which travelled close to the surface for up to several metres. Once I severed these from the parent plant, they sent up suckers. Removing these when very small revealed that the individual plants had still to develop their own root system and were just drawing nourishment from the original old root. Subsequent development of these plants was much slower than that of plants which were left a week or two longer and were obviously developing their own root system.
Moreover, the length of old root taken together with the sucker seemed to have little if any relationship to how well the plant subsequently developed. I am not a tetrapanax nursery so I set about carefully removing as many of the original roots as possible. Out of curiosity, I put 0.5m lengths of these into a nursery bed to see how readily these root cuttings produced plants. Some weeks later, all the roots had rotted without any signs of further plant development. I leave it to you to draw conclusions. So much for propagation tips – because, sooner or later, you will get suckers!
Easy to get hold of
Several years after the giant tetrapanax variants burst onto the European plant scene and after my story, it isn’t surprising to find that they are now fairly easy to get hold of. Reports over the internet confirm that their suckering nature can indeed be a problem.
Therefore the question arises as to how well the giant tetrapanax variants will develop if confined by some root restricting device such as the foil sold to limit the spread of some bamboos. I suppose a sort of alternative would be to grow the plant as a specimen in its own bed in a lawn. Suckers would then presumably be mown off. Simply putting Tetrapanax into a mixed border seems to be tempting fate a bit too much from what I have seen. My experience taught me that the plant certainly thrives on moisture and food. The roots had made straight for the manure around the Gunnera and the banana (Musa sikkimensis).
A spectacular plant
Steroidal Giant” (and presumably “Rex“) are undoubtedly spectacular plants when grown well as the photographs illustrate. I was struck by the way some suckers had developed quite well in very deep shade behind other plants. The literature does state that planting can be done in half-shade. Furthermore my last observation prompts me to ask just how tolerant of shade the Tetrapanax is. This is certainly something I will be putting to the test in our woodland in 2009. In general, an increase in the shade tends to enhance leaf size so if this holds for Tetrapanax, then who knows what will happen.
|Typhonium (Sauromatum) nubicum “Voodoolelie”|
Wollemia is a genus of coniferous tree in the family Araucariaceae. It was only known through fossil records until the Australian species Wollemia nobilis was discovered in 1994 in a temperate rainforest wilderness area in New South Wales. This remote area of the steep-sided sandstone gorge 150 km north-west of Sydney is now known as the Wollemi National Park i
Wollemia nobilis is an evergreen tree reaching 25–40 m (80–130 feet) tall. The branching is unique in that nearly all the side branches never have further branching. After a few years, each branch either terminates in a cone (either male or female) or ceases growth. After this, or when the cone becomes mature, the branch dies. New branches then arise from dormant buds on the main trunk. The leaves are flat linear, 3–8 cm long and 2–5 mm broad. They are arranged spirally on the shoot but twisted at the base to appear in two or four flattened ranks.
The discovery, on or about 10 September 1994, by David Noble, a field officer of the Wollemi National Park in Blackheath, in the Blue Mountains, only occurred because of his adventurous bushwalking and rock climbing abilities. Noble had good botanical knowledge, and quickly recognised the trees as unusual and worthy of further investigation. Returning with specimens, and expecting someone to be able to identify the plants, Noble soon found that they were new to science. The species was subsequently named after him. Further study would be needed to establish its relationship to other conifers.
The initial suspicion was that it had certain characteristics of the 200-million-year-old family Araucariaceae, but was not similar to any living species in the family. Comparison with living and fossilised Araucariaceae proved that it was a member of that family, and it has been placed into a new genus with Agathis and Araucaria. Fossils resembling Wollemia that are possibly related to it are widespread in Australia, New Zealand and Antarctica. However Wollemia nobilis is the sole living member of its genus. The last known fossils of the genus date from approximately 2 million years ago. It is thus described as a living fossil, or alternatively, a Lazarus taxon.
Fewer than a hundred trees are known to be growing wild, in three localities not far apart. It is very difficult to count them as most trees are multistemmed and may have a connected root system. Genetic testing has revealed that all the specimens are genetically indistinguishable, suggesting that the species has been through a genetic bottleneck in which its population became so low (possibly just one or two individuals) that all genetic variability was lost.