Tropical garden with “exotic” plants – One of the eight gardens of “OpdeHaar”
On this page on the tropical garden you will find information on:
- Experimental garden
- What are “exotics” – something that looks tropical!
- The role of exotic plants in the garden
- Cold temperature tolerance
- Experimenting with cold temperature tolerance
- Bananas in The Netherlands
- Agaves (2006)
- Hibiscus of Newbiscus “Mauvelous”
- Melianthus major
- Tetrapanax papyrifer
- Other exotic plants in other borders
- Internet sites
Before giving my definition of “exotics” and the role of exotics in the garden we will first wet your appetite by naming some of the “exotics” which can be found in the Tropical Garden at OpdeHaar. More details on many of the plants are given in later sections. Many of the “exotics” in our garden are collected in the Tropical Border and the following plants are doing well:
- Musa basjoo (Japanese fibrebanana) (Click here for more information on banana plants)
- Typhonium (Sauromatum) nubicum – giant or Nibische voodoo lily
- Tetrapanax papyrifer “Steroidal Giant” rice paper plant
- Melianthus major
- Clerodendrum bungei
- Fatsia japonica “Aureovariegata” – Japanese fingerplant
- Elsholtzia stauntonii “Alba”
- Nandina domestica – heavenly bamboo
- Ginger species:
- Hedychium maximum en spicatum,
- Roscoea purpurea en “Brown Peacock” selection,
- Roscoea australis,
- Roscoea auriculata “White Cap” en “Floriade”
Since 2008/9 the tropical border has become more of a test bed. The groundcover Echeveria were very successful but needed to be dug up and overwintered, frost-free, in the greenhouse each year and in 2009 I decided to discard them in favour of a more permanent planting. Phormium ”Bronze Baby” grew into quite a giant. In winter, I tied the leaves together and surrounded it by dry leaves kept in place by bubble plastic. There was no frost damage at all. In 2008/9, I decided to see what would happen if I just left it unprotected. The long, cold spring of 2009 basically killed the top growth. Although it slowly started to come from the base it was clearly not a plant which could survive reliably without protection. I removed it and am growing the new plants in pots.
The future rule for me is simple – protect all phormiums, cordylines and flaxes such as astelias. Although the roots of such plants may survive a mild winter, subsequent regrowth and recovery is just too slow and messy to justify not protecting them each winter. We currently put out various decorative phormium varieties in pots or as summer bedding in the ”Fire and Ice” garden and I may adopt this strategy in The Tropical border.
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.
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 trialled 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. Indeed 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.
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!)
There is so much to say about the bananas growing in our tropical border that we have devoted a separate page to them.
Just to wet your appetite here are some photos taken in our garden
Our interest in gingers was first aroused as many are light shade loving plants and that is always a plus point with our large woodland garden. Zingiber mioga was a winner in the Millennium garden and its flowers in a shady area stimulated the acquisition of various hedychium and roscoea varieties for various areas of the garden including the Tropical border.
The loss of Canna “Durban” due to rotting (see next section) made room for a roscoea collection – Roscoa purpurea and Roscoa purpurea “Brown Peacock”, Roscoa auriculata “White Cap” and Roscoa “Floriade”. During August and later they are reminiscent of an out-of-season iris. Inspite of the fact that they do keep flowering, they tend to fall over and are not really suitable for someone who likes to keep everything neat and tidy. Incidentally these roscoea are all in the light shade cast by Musa Basjoo and some high miscanthus grasses. The roscoea all came from René Zijveld and were all potted up as tubers in March 2006 and planted out in May. There is an excellent book by T.M.E. Brannery, “Hardy Gingers” in the R.H.S. Plant Collector Guide series (ISBN 0-88192-677-9) which we can highly recommend.
We grew Canna “Durban” for its foliage – flowers are an added bonus. (The “Pretoria” variant substitutes a yellow background for the purple-red of “Durban” for those interested in alternative colour schemes.) Like many gardeners, I have accidentally left both canna and dahlias in various bits of the gardens in past years. Most of these survived our recent milder winters without protection to emerge unexpectedly the next year. In the autumn of 2005 I had a really vigorous clump of Canna “Durban” and decided to try over-wintering them in the ground under a mulch of rotted cow manure topped by 20cm of dry leaves under a roof of bubble plastic to ensure dryness.
What could go wrong!? Well, in common with several other people who tried over-wintering cannas in the ground that winter, I am afraid they just rotted in-situ. One can speculate that the long, cold spring of 2006 was to blame; temperatures were too low to stimulate growth but were enough for destructive fungi to really get to work. Interestingly in this respect, I have had a canna for about 10 years in a sheltered spot under a south facing wall that has popped up annually without any protective intervention by me. The fact that it also vanished in 2006 does indeed tend to fuel my speculation of the importance of a sustained start into growth in spring. My initial thought was to just replace canna but I could not find either “Canna Durban” or Canna Pretoria”, so I have planted the spot with hardy roscoea. (see previous section)
The real experiment tin 2006 came in the form of the cold hardy agaves and prickly pears. For those interested, I had Agave neomexicana and Agave havardiana along with Opuntia compressa, fragilis, macrorhiza and polyacantha. A quick reference to the Internet reveals that they are tolerant to temperatures as low as -25°C in dry desert conditions. My attempt to ensure winter dryness came in the form of a bubble plastic tent that unfortunately partially collapsed onto two Agave neomexicana and an Opuntia polyacantha. The Opuntia survived, although damaged with bits broken off, but both the Agaves were nearly killed – they got wet and rotted extensively. This accident was my own stupid fault but I’ve “used” it as an opportunity to re-design this central part of the tropical border.
We introduced three new plants into the tropical border that really came into their own in 2006:
- Hibiscus or Newbiscus “Mauvelous”
- Melianthus major.
- Tetrapanax papyrifera “Steroidal Giant”
As far as Europe and The Netherlands are concerned, the hardy large-flowered hibiscus introduced in 2005 is a real breakthrough. It first appeared in USA around 2000 from the Gilberg Farms nursery under the hybrid name “Matterhorn”. It is registered here, with breeder’s rights, under the names of “Newbiscus” and “Mauvelous” (not “marvellous!”). This hardy perennial is suitable for a sheltered place in the sun and gets to around a metre high. Spectacular, soup plate sized flowers appear from about August and continue into autumn.
I got our plant in 2005 and was surprised to see it emerge from the ground in the Tropical Garden after no special winter care, in the spring, as claimed. It is a cross between Hibiscus syriacus and Hibiscus moscheutos and is a pink variant; in USA red and white hybrids are available and it is said that these will soon be available here. Of additional interest to me was that the Newbiscus can be treated in cultivation as a standard border plant in contrast to Hibiscus moscheutos (swamp hibiscus) which needs really moist conditions before it will flower.
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 the 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 from seed
This plant 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.
I first heard about this exotic member of the Aralia family in 2005 from a friend from whom I got my Tetrapanax “Steroidal Giant”. Reference to the internet revealed that, as its common name of “Rice paper plant” suggests, it is used to make 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 papyrifer itself which is a much smaller plant and is reported to be 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.
Tetrapanax needs room!
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 papyrifer and “Steroidal Giant” for comparison in his catalogue.
My “Steroidal Giant” was planted out in the Tropical garden 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. Coincidentally, this was one of the wettest on record in The Netherlands. This prompted the steroids to kick in and it had 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 sikimensis 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 take out the trunk with a very generous portion of root. It never even made an attempt to make growth. 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.
Tetrapanax root system
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. Apparently, they 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. These were obviously developing their own root system. Moreover, the length of old root and sucker combined didn’t seem to influence how well the plant subsequently developed.
Out of curiosity, I put 0.5m lengths of these roots into a nursery bed. Some weeks later, all the roots had rotted. So much for propagation tips – because, sooner or later, you will get suckers! Therefore, 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. So the question arises as to how well the giant tetrapanax variants will develop if confined by some root restricting device. My experience taught me that the plant certainly thrives on moisture and food.
“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.
Decaisnea fargesiiI have just moved 3 Decaisnea fargesii from the tropical border to other areas of the garden. Their claim to fame comes in the form of long blue seed pods in autumn. For those who have not grown it, Decaisnea fargessii is quite hardy, readily available and also easy to grow from seed. It is decoratively unremarkable except for its blue seed pods in autumn, as shown in the photograph. I personally would not waste space on it in a smaller garden. However, the tactile quality of the pods never ceases to fascinate me. They look like they should be hard and unyielding much as a broad bean or pea pod. When you touch them, they are unexpectedly soft and yielding and contain seed in a gel that looks more like frog spawn than anything else.
As I’ve said earlier, the tropical border is not the only place where we have exotics and more tender plants. Years of success with my Opuntia humifusa growing and thriving in the dry soil against the garage wall along with Arbutus unedo, Erica arborea “Albert’s Gold”, Phlomis chyrsophylla, Daphne cneorum, Trachelospermum jasminoides variegatum are evidence to what one can bring through Dutch winters in a sheltered, dry border. These latter plants generally don’t get any special protection in this position. A rather sizeable Trachycarpus fortunei, (Chusan palm) only kept free of snow on the leaves, is getting up to the first floor.
There is a lot of interest in pushing out the boundaries of exotics. Virtually every time I visit the internet or look at recent book publications, I come across something new and interesting. Some sites I find useful from our base in The Netherlands are:
- De Groene Prins: www.degroeneprins.nl
- Bamboo nursery Kimmei: www.kimmei.com
- Tropical Centre: www.tropicalcentre.com
- For seeds: www.jungleseeds.co.uk
An extensive website with many interesting links and a blog is: