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Graham Rice on Trials

Updates on trials and awards from the Royal Horticultural Society by Graham Rice

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  • Dahlias in containers

    Graham Rice on 28 Oct 2009 at 11:29 AM

    Dahlia 'Spanish Conquest' in the Wisley trial of dahlias in containers. Image: ©GardenPhotos.comThis year's dahlia trial at Wisley has been unusually fascinating and I'll be reporting on a number of its features over the next few weeks. Picking up on recent trends, this year twenty one of the entries were grown as individual plants in pots to assess their value as container plants.

    Immediately one thing is obvious. These plants, of course, are smaller than most dahlias - if they were 4ft/1.2m tall, as are many varieties, they'd be far too large for most containers. So we tend to look down on the flowers from above. But many varieties hold their flowers so they face sideways - ideal on a tall plant which is viewed from the side but the impact is much reduced when you look down at the flowers on a short plant from above.

    ‘Spanish Conquest' (above, click to enarge) was one whose flowers are more upward facing and which made a real impact. The colour is wonderful too, with red buds opening to old gold flowers with burnt orange centres. The plants were prolific and seemed to cope with dry conditions better than many. I thought it the best of all those grown in containers this year.

    Dahlia 'Keith's Pet' in the Wisley trial of dahlias in containers. Image: ©GardenPhotos.comOn the other hand there was ‘Keith's Pet'. This is a lovely dainty little dahlia with neat dark purplish foliage and bright white flowers with just a hint of pink showing through from the backs of the petals. But the flowers face sideways and unless you get down on your hands and knees - as I did to take the photograph - you never get the full impact of the flurry of flowers.

    Other outstanding varieties in containers were ‘Exotic Dwarf', a single yellow with upward facing flowers, ‘My-nute Blend', a very prolific red and yellow double, and also ‘Gallery La Tour', with upward facing pink and white double flowers over dark leaves.

    There were a couple of other points that came out of this trial of container grown dahlias. There was no watering system set up, no drip nozzles so that the pots could be easily watered at the turn of a tap. The result, I'm afraid, was that with pressure of work meant that the watering can just didn't come out often enough and many varieties would have been a great deal more impressive if properly watered.

    And as we assessed them we also noticed the compost in the pots. It had shrunk so much that there was a large space between the tops of the pots and the compost. We concluded that the peat-free compost had already started to decompose and so had shrunk - not good for the plants. The begonias hated the peat-free compost this year as well. Sometimes, nothing but peat, or at least a good proportion of peat, will do.

    Of course the varieties that could cope with these problems really were impressive.


  • Double display from delphiniums

    Graham Rice on 21 Oct 2009 at 01:57 PM

    One of the glories of the Wisley trials field in early summer are the delphiniums. Tall and magnificent - taller than they ever get in most people's gardens, I have to say, what with all that manure - they're a real spectacle. But then after a few weeks of glory, they're gone. Or are they?

    Delphinium 'Amadeus' flowering in September in the Wisley trials. Image: ©GardenPhotos.comI went back to take a look at the delphinium  trial in mid September, and then finally at the very end of the month, and found some varieties again looking very impressive. OK, the quality of the individual spikes was not up to the standard of the main display but they nevertheless made a real impact.

    On my first September visit ‘Ann Woodfield', blushed white, and ‘Kestrel', electric blue with a dark eye, stood out while at the end of the month ‘Jenny Agutter' (right), in rich pink, and ‘Amadeus' (above), in deep purple blue, were the stars. Delphinium 'Jenny Agutter' flowering in September in the Wisley trials. Image: ©

    So what can we do to help ensure we get a double display from our delphiniums? First, cut off the main spike as it fades and then when the shorter, slimmer secondary spikes that follow also fade away - cut the whole plant back down to ground level.

    This may seem an odd thing to do in mid summer but if the plants are kept watered, and fed with a high nitrogen fertiliser if the soil is not as rich as that at Wisley, they will soon sprout fresh new leaves. These are valuable in themselves and then followed by more flowering spikes later. Be sure to look out for mildew in hot dry spells and also for caterpillar damage. Then you've every chance of getting a double delphinium display from your plants.


  • New (free!) dahlia bulletin

    Graham Rice on 12 Oct 2009 at 04:52 PM

    Open-Centred Dahlias - new Plant Bulletin from the RHS. Image: ©RHSDahlias are becoming increasingly fashionable. In particular, single-flowered and collarette dahlias are catching everyone's eye so after trialling many of them in recent years the RHS has produced a twelve page full colour bulletin entitled Open-centred Dahlias.

    Written by Wisley's Sue Drew, from RHS Trials Office, who has special responsibility for the dahlia trials, the bulletin covers both single-flowered types and collarette dahlias (collarettes are those with additional shorter petals around the eye).

    This excellent guide starts with a short history of the dahlia and then illustrates all the thirteen different flower forms, to show the amazing range available. A wide range of the best singles and collarettes is illustrated and each is briefly described, all those chosen have either already been honoured with an Award of Garden Merit or look well set to gain the award soon. Suppliers are noted for each variety - very useful. There's also a very good guide to growing dahlias, a discussion on breeding new dahlias and some thoughts on planting partners for single dahlias.

    The whole bulletin provides a valuable introduction to these long flowering and prolific plants, all written in an easy to follow style and with plenty of excellent pictures.

    What's more, you can download this new Dahlia bulletin FREE from the RHS website. Or check out the RHS Plant Bulletins page for a list of all the free Plant Trials Bulletins on offer.

    Yet another excellent RHS Plant Bulletin based on the society's trials.



  • Intriguing ipomoeas

    Graham Rice on 07 Oct 2009 at 03:54 PM

    The trial of annual climbers at Wisley has thrown up some stars and some disappointments. Both extremes are to be found amongst the ipomoeas.

    Mina lobata in the Annual Climbers trial at the RHS Garden at Wisley. Image: ©GardenPhotos.comIn recent years botanists have decided that, although superficially it looks very different, Mina lobata is so closely related to Ipomoea that it should be moved into the genus Ipomoea as Ipomoea lobata (left, click to enlarge). It's been a real star, with spikes of flowers featuring bright red buds opening to cream. Three very similar entries were included in the trial and in recent weeks all three have been stunning and all three look to be on track for an Award of Garden Merit. And all three looked impressive all day.

    Also pretty impressive was Ipomoea ‘Ismay Soft Blue' (below, click to enlarge), with its white flowers neatly barred in blue and late in the season it seemed to have the most flowers on show of any ipomoea. Ipomoea 'Ismay Soft Blue' in the Annual Climbers trial at the RHS Garden at Wisley. Image: ©GardenPhotos.comThe deep purple ‘Kniola's Black Night', with its white throat, set against small, dark foliage was also good. This and the other familiar trumpet-flowered ipomoeas all open very early in the day and on hot sunny days have crumpled by lunch time although on cool days ‘Ismay Soft Blue', in particular, lasted till the end of the day.

    However our old favourite ‘Heavenly Blue' - such a stunning colour - and many of the other ipomoeas proved too leafy on the rich Wisley trials field soil and, as happens with nasturtiums, the leaf stalks stretch and so the leaves tend to hide the flowers. The same thing happened with the thunbergias. The ipomoea leaves themselves also grew larger than normal and there seemed to be far more of them. The result of all this extended leafy growth was that the flowers were often hidden. Some were also rather variable in their flower colour or patterning and these included ‘Flying Saucers' and ‘Azzurro di Venezia'.

    Those Ipomoea lobata may have started later than most of the annual climbers but the autumn display is amazing.