EXOTIC PLANTS AND/OR UNUSUAL PLANTS at OpdeHaar gardens
On this page we look at:
- What are exotic plants?
- The role of exotic plants in the garden
- Exotic plants in our tropical border
- Explosion of new plants
All photos were taken in our garden
Click on the photos for a larger image and a slideshow.
“What are exotic plants?” That is the question. 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 plant” 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.
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 exotic plants come into their own, particluarly in the tropical border.
Many of these exotic 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.
Exotic plants in our tropical border
The Tropical border is home for many of our “exotic plants”. 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 trialled 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.
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 “exotic plants” or plants with 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. 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 below of plants at the end of the first growing season in our garden gives an idea of the size and the foliage :
For more information on Geranium yeoi, click here.
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. Our melianthus majof survives quite happily in the sheltered tropical border.
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 is a member of the family Araliaceae along with Fatsia, Aralia, Hedera, Schefflera and Oplopanax. My “Steroidal Giant” was planted out in a suitably moist and sheltered spot in the tropical border in full sun early in 2006. 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. 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.
For more information on Tetrapanax, click here.
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.
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.