| The Tropical Border |
Before giving my definition of "exotics" and the role of exotics in the garden we will first wet your apprtite by naming and showing you photographs of some of the "exotics" which can be found in "Op de Haar" gardens. 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 at the close of 2006 the following plants were doing well:
- Gunnera chilenesis (syn. G tinctoria)
- Gunnera manicata (see photo below)
- Musa basjoo (decorative Japanese banana)
- Musa sikkimensis (syn. M. hookerii) (Sikkim banana)
- Phormium tenax “Bronze baby”
- Cordyline australis “Zuidland” (hardy cabbage tree?)
- Typhonium (Sauromatum) nubicum – the “Voodoo lily” (see photo below)
- Tetrapanax papyrifera “Steroidal Giant”
- Hedychium maximum and spicatum
- Roscoea purpurea and “Brown Peacock” selection
- Roscoea australis
- Roscoea auriculata “White Cap” and “Floriade”
- Pelargonium endlicherianum (Turkey)
- Olearia x scillionensis (Tasmanian daisy bush)
- Cytisus battandieri
- Melianthus major
- Clerodendron bungei (See photo below)
- Fatsia japonica “Aureovariegata” (see photo below)
- Nandina domestica (Heavenly bamboo, see photo below)
- Paulownia tomentosa (see photo below)
Since 2008/9 the tropical border has become more of a test bed and some plants such as the Tetrapanax are being tried in various other areas in the garden. 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 and 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 'n Ice" garden and I may adopt this strategy in The Tropical border. As I write these lines looking out at a covering of snow in January 2010, I'm really still awaiting a Damascus Road sort of revelation as to how I will go forward with the central part of the tropical border. I have a selection of seeds of vividly coloured coleus, osteospermum, mesembryanthemums and dahlia as a fallback for 2010 - on reflection, those echeveria weren't all that bad!
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| Gunnera manicata | Fatsia japonica |
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| Clerodendrum bungei | Nandina domestica |
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| Paulownia tomentosa tree | and flower |
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| Typhonium (Sauromatum) nubicum “Voodoolily” |
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| Echeveria elegans |
As mentioned above we used to use Echeveria elegans as a sort of low ground cover. These plants are not winter hardy but are so easy to store in baskets under the greenhouse staging that I was willing to break a rule for them. We have several sorts of opuntia cacti in pots and in other areas near the Tropical Border – I need to find a dry position for these plants, where visitors will be safe from their spines!
Exotics are not limited to the Tropical Border. In the rose garden, you will find Trachycarpus fortunei (Chusan palm) (photo below), Arbutus unedo “Rubra”, (the strawberry tree, photo below). Camellia, bamboo, hardy gingers, various arisaema and asarum sorts are also distributed throughout the gardens.
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| Trachycarpus fortunei |
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| Arbutus unedo "Rubra" |
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. Unusually coloured leaves such as found on some 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 “Op de Haar” 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 (see photo right). 
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 (photo below) 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, (see photo right of Trachycarpus fortunei in flower in May 2006) 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.
Just to show you how we protect our more tender plants in winter there is a photo below in the section on Cannas of our tropical garden in winter and here is a photo of the overfull greenhouse (after all I said!).
Fatsia japonica Trachycarpus fortunei
Our greenhouse in winter
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Musa basjoo
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Water, food and sun
The property of “explosive growth” in bananas and some other sub-tropical plants depends on providing ideal growing conditions i.e. the right amount of food, water and adequate temperature along with plenty of sun. However, some bananas such as M. itinerans come from shady woodlands in their native habitats in Yunan. (This particular plant is potentially the tallest banana but I understand that its overwintering properties are difficult and this was confirmed when it failed to resurrect after a winter which gave no problems for either M.basjoo or M.sikkimensis.) Food comes in the form of a good mulch of well-rotted manure, courtesy of my neighbour and his cows, that I supplement with general-purpose fertiliser. In practise, the manure accounted for about 95% plus of the food and we have been rewarded with massive, healthy leaves but no flowers or fruit until 2009. However, more on this topic shortly. The tropical border is on just about the highest and driest bit of the garden so I cater for sufficient moisture by creating subterranean ponds under both bananas and gunnera. This amounts to putting saucer-shaped agricultural foil about 1 to 1.5m below the surface under the central part of the plants. Roots then find their way in and around this. In the long, dry periods a few minutes with the hosepipe are all that are needed to replenish stores for a week or two.
Winter protection
In the winter, I put down a good layer of dry leaves with a roof of bubble plastic which serves the dual purpose of keeping frost away from the roots and the base of the stems and stopping my “ponds” from building up water which might conceivably rot the roots of the bananas. A combination of too much water at a time when the plant is not growing is a potently fatal combination for many plants, especially the more tender ones. Banana stems are effectively columns of water held in place by vegetative cells that rupture the moment the water freezes.
Spring explosion
In Spring new growth comes from the centre of the old shoots. If you carefully cut back the stem in spring to the point where it is green in the centre, this is far enough.
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Musa sikkimensis
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The temperature in Spring has noteworthy effects on tempting bananas into growth. The Spring of 2006 was especially long and cold and M. basjoo started into growth and developed slowly from green stems about 80cm high which I had brought through the winter. With M. sikkimensis (photo left) a green point seemed to be starting to push out from the centre of 3 seemingly healthy green stems and on a rare warm, sunny day,. However, this start into growth simply stagnated and the stems basically degraded over several weeks. They did not go black and mushy which would be symptomatic of frost damage and rotting but just seemed to die such that playing a hosepipe on them easily peeled off the stem steadily lower and lower with no sign of life. It is difficult to describe but suffice it to say that M. basjoo stems remained solid and robust under similar treatments. M. sikkimensis simply came strongly from new basal shoots once the weather really warmed up. I have shared my observations on this behaviour with other friends, notably Hans Prins, who were not surprised by M. sikkimensis’s reluctance to grow from an over wintered stem like M. basjoo. As global warming tempts more gardeners to experiment with exotics, particularly with decorative bananas, a comparative study of the effect of Spring temperatures would arouse widespread interest.
Flowers, fruit and fertilizer
The winter of 2008/2009 in The Netherlands was the first in a number of years which approached something one could describe as having prolonged low temperatures - after Christmas there was a protracted cold spell during which we experienced -8 deg C and then spring was preceded by a cold spell. I took the protecting dry leaves from around our Musa basjoo clump on 1 April which is later than I've ever done this in previous years. It commenced growth much later than ever before and to the extent that I was wondering if the long, cold spell had almost killed a lot of it. However, once it started into growth, it soon put out its characteristically massive leaves from the ~1m high stumps which soon developed into sturdy trunks up to 3m high with leaves to ~4m and more. Business as usual, or so I thought. I was walking round the garden with visitors right at the end of September when I noticed that a flower was forming on one of the stems. It wasn't immediately very visually spectacular because it couldn't have been positioned in a much more difficult place for it to be viewed but the accompanying photo gives an idea of how it appeared to a passer-by. I delayed cutting back the stems of the banana until the first frost was certain to let the fruiting process progress as far as possible. (It is noteworthy that November 2009 was the mildest on record here with temperatures often well over 10 deg C even at the end of the month.) In the first week of December, a high pressure area moved in such a way as to pull cold north-easterly winds over us and frost finally came on the night of 12 December 2009. It was very clearly predicted and on 10 December I cut down the M.basjoo stems to ~1m high and completed the winter protection. I then discovered that two other stems were producing flowers. We cut off the flowers and the photographs below (with cm ruler) give an impression of what you can expect.
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| M. basjoo in bud on the plant | M. basjoo bud and small bananas |
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| M. basjoo flower | M. basjoo flower |
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| Stamens of M. basjoo flower | Small bananas forming |
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| Small bananas forming | Small bananas forming |
The big questions in my mind are what was special to cause flowering for the first time this year and what can we do to render this a regular event, short of constructing a winter greenhouse around our Musa basjoo. As with many things these days, I turned to the Internet for inspiration. When one does a dedicated search on "fruiting and flowering", it becomes clear that other gardeners in cooler climes also share the sort of experience I have described. However, there is nothing of substance to be found which describes how to set about getting regular fruiting and flowering under the sort of growing conditions which we have here in the central Netherlands where one really has to assume that winter minimum temperatures will hit at least -10 deg C with the knowledge that they can also go much lower despite all the milder conditions which increasingly occur. An article from New Zealand ( http://www.subtropical.co.nz/writingBanana06.html ) basically summarises the sort of cultivation requirements to favour fruiting in Musa basjoo. In summary, get leaf production going as soon as possible and ensure that potash (potassium) is available to promote flowering and fruiting. Thinking back, the cold 2009 spring certainly didn't help with early leaf production although it did commence from good, thick stems about 1m high and which were at least 2 or 3 years old . In previous years, growth also came from protected stems but feeding was limited to a good load of well-rotted cow manure on the philosophy that it needed plenty of nitrogen to put back all the green stem and leaf I took off it prior to winter. In 2009 I was rearranging the tropical border and the banana was basically left to get on with things but I did throw it generous handfuls of a general fertilizer at regular intervals. In other words, for the first time in it's life, our Musa basjoo received a balanced diet and not one incredibly rich in nitrogen. When one recalls that one symptom of a plant which is fed on a diet of fertilizer in which one of the key NPK components is essentially overdosed is an apparent deficit of the other two main components, then the lack of flowers on an otherwise very vigorous banana clump is possibly explained. I have been part-starving it in my drive for maximising leaf growth! The verification of this hypothesis will follow in 2010 - watch this space or, better, come and see for yourself !
More information
For information, a very interesting article entitled "The origin of Musa Basjoo" by David Constantine in the Plantsman, (vol 7, part 3, p156-161, 2008) points out that the popular association with the "Japanese fibre banana" is quite possibly incorrect. Fibre is/was produced from a less hardy banana grown on the Ryuku islands and nobody less than von Siebold compounded the confusion. M. basjoo is most likely a purely decorative garden plant which Japanese gardeners introduced from China.
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 - R. purpurea and R. purpurea "Brown Peacock", R. auriculata "White Cap" and "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.
Canna
We grew Canna “Durban” (photo left) 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. 
Canna "Durban"
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. (See photo below of tropical border in winter.)
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| Banana's packed up for the winter |
What could go wrong!? Well, in common with several other people who tried over-wintering cannas in the ground last 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 “Durban” or “Pretoria”, so I have planted the spot with hardy roscoea. (see previous section)
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| Agave neomexicana |
The real experiment tin 2006 came in the form of the cold hardy agaves and prickly pears. For those interested, I had A. neomexicana (see photo on left) and A. havardiana (photo at the top of this page) along with Opuntia compressa, fragilis, macrorhiza and polyacantha (see photo on left below). 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 (photo right).
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| 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 border.
Fancy leaves, fancy flowers and fancy fruit
We introduced three new plants into the tropical border that really came into their own in 2006:
- Hibiscus or Newbiscus “Mauvelous”
- Tetrapanax papyrifera “Steroidal Giant”
- Melianthus major.
Hibiscus or Newbiscus “Mauvelous”
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| Hibiscus/Newbiscus “Mauvelous” |
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” and was introduced into Europe by Green Works International of ‘t Zand in The Netherlands (http://www.green-works.nl/nl/bol-vasteplant/newbiscus//). It is registered here, with breeder’s rights, under the names of “Newbiscus” and “Mauvelous” (not “marvellous!”). It is a hardy perennial 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 after no special winter care, in the spring, as claimed. It is a cross between Hibiscus syriacus and H. 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. I suppose it all depends on how Green Works can get them through the tissue culture and also on commercial planning! 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
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| Melianthus major |
Melianthus major (photo left) 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.
Provided the roots are protected from frost and kept dry, M. major is easy in cultivation. Getting hold of plants is more difficult but if one cannot find them, I can testify from personal experience, that they come very easily from seed that is readily available. In our tropical border M. major forms bushy plants up to 1.5m high and 1m across by about August.
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| Tetrapanax papyrifera "Steroidal Giant" (October 2006) |
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| Gunnera mannicata | Typhonium (Sauromatum) nubicum “Voodoolelie” |
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| Musa sikkimensis behind tetrapanax papyrifera |
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 (M.sikkimensis).
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| Tetrapanax papyrifera "Steroidal Giant" (August 2007) |
Poncirus trifoliata
In the summer borders our only hardy citrus plant, Poncirus trifoliata (Japanese bitter orange) (photos left) 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 ( photo below left) 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 (photo below right) that ripen into tomato-sized yellow fruits in the autumn (see photo below right). It came from N. china to Europe in 1850 and does best in full sun and is perfectly hardy without winter protection.
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| Poncirus trifoliata |
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| Poncirus trifoliata fruit | and flowers |
Other exotics
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| Decaisnea fargesii |
I 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 (photo right). 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 balcony.
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| Begonia grandis |
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| Begonia grandis |
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Impatiens omeiana |
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| Impatients omeiana |
Internet sites
There is a lot of interest in pushing out the boundaries of exotics and 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:
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Charley Younge’s kwekerij en bamboepark (Schellinkhout): www.bamboe-ic.nl
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Bamboekwekerij Kimmei (Valkenswaard) : www.kimmei.com
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Kwekerij de Groene Prins: www.degroeneprins.nl
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Tropical Centre: www.tropicalcentre.com
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For seed: www.jungleseeds.co.uk
Primarily for the Dutch, another excellent site is:
- General info and links: http://home.planet.nl/~gerrien/
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