The plant collections at OpdeHaar gardens – EXOTIC OR UNUSUAL PLANTS

On this page, information about and / or photos of amorphophallus, arbutus, decaisnea, gunnera, melianthus, nandina, poncirustetrapanax, en wollemi pine

 

All photos were taken in our garden.

Click on the photos for a larger image, a slideshow and sometimes extra information.

 

 

What are exotics?

Hedychium “Tara”

Nothing would be easier than to simply omit discussion of this question and just leave it to intuition but 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 to say nothing of the 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 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 in the form of mulch or wind protection – nothing incredibly 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.

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” in the garden from around August to 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. Many or our “exotics” are in a dedicated border  – “ The Tropical Border.” 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 and the temperature may even surprise you in the middle of winter. The current planting started in 2004 and 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 and South America, not to mention continuing finds in 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 and 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. 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 and 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 10 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) and 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.

 Fatsia japonica
Trachycarpus fortunei
 Fatsia japonica  Trachycarpus fortunei
Our greenhouse in winter

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!).

Amorphophallus

 

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 and 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. and 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.

Konjac is fairly easy to grow and responds gratifyingly to heavy organic feeding. In Japan, planting in holes enriched with manure is widely practised. As the photographs show, I have used slow-release fertiliser in the pots with acceptable results.   Konjac needs to be kept moist throughout the growing season and 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 and some people advise giving a final potash-rich feed at this stage. 

 

Arbutus

Decaisnea

Gunnera

Melianthus major

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 and 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. The root system is pretty compact for what can be a sizeable shrub (1.5 x 1m) by year-end 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. As I said, 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.

Nandina domestica

Poncirus trifoliata

  In the summer 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.

Poncirus trifoliata fruit Poncirus trifoliata fruit and thorns Poncirus trifoliata flowers

 

 

Tetrapanax papyrifera

 

 Tetrapanax papyrifera “Steroidal Giant” (October 2006)

 

I first heard about this exotic member of the Aralia family in 2005 from a friend from whom I got my Tetrapanax “Steroidal Giant” early in 2006. Reference to the internet revealed that, as its common name of “Rice paper plant” suggests, it is used to make a paper in Asia. It occurs naturally in southern China and Taiwan. Spectacular variants of the plant are now increasingly common in the trade under the names “Steroidal Giant” and “Rex” and to my eye these appear very similar to each other. However, they are indeed distinct from the Tetrapanax papyrifera itself which is a much smaller plant and to judge from reports on the Internet, is significantly less winter-hard than the giants I’m talking about here which form a stem/trunk and can reportedly withstand temperatures as low as -15°C. Our recent mild winters haven’t allowed me to verify this but more on this later.

  There also appears to be some confusion or a variation in the nomenclature in the spelling of papyrifera” and variants which commonly occur are papyrifer, papyrifera, papyriferum and papyriferus in conjunction with “tetrapanax” as a consistent feature.    Tony Avent of Plants Delight Nursery in USA gives some clues as to the origins of the giants in the nursery trade besides having good photographs of both Tetrapanax papyrifera and “Steroidal Giant” for comparison in his catalogue. 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 – 4mwould have been just enough in my case.

 

Finally in the spring of 2008 I decided to shift the thing and 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! 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 and so 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). 

 

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 and my last observation prompts me to ask just how tolerant of shade the Tetrapanax is and 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”  

 

Trachycarpus

Wollemi Pine

Wollemia is a genus of coniferous tree in the family Araucariaceae. Wollemia was only known through fossil records until the Australian species Wollemia nobilis was discovered in 1994 in a temperate rainforest wilderness area of the Wollemi National Park in New South Wales, in a remote series of narrow, steep-sided sandstone gorge 150 km north-west of Sydney. 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.

 
Wollemi nobilis
Discovery

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, but 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.

Source: Wikipedia

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