When I saw the Wisley trial of forty seven different forms of Hydrangea paniculata last September I was impressed. These are easy and dependable summer and autumn shrubs whose shapely blooms provide attractive colour from bud to faded flower And this week's publication of a free-to-download full colour bulletin on the trial reminds me what a wonderful sight they were.
You may also have seen the well-established specimens on the walk up Battleston Hill from Wisley's double herbaceous border - they're stupendous.
But until I saw the trial I'd not realised that some age far more harmoniously in colour than others. The trial judges kept that in mind and plants were also judged for their habit, their response to pruning, for the colour of their buds, flowers and faded flowers and the shape of their flower heads, and for how their heads were held (upright or floppy); stem colour, and summer and autumn foliage colour were also assessed. Ten proved worthy of the Award of Garden Merit.
But there was much more to this trial than simply judging the quality of the plants. Two pruning trials were also carried out.
There were three plants of each variety in the trial: one plant was pruned hard, one pruned moderately, and one simply dead-headed. The treatments had a very noticeable effect on flowering time and flower size. In the other pruning trial, additional plants were pruned either in February, March or April. This too influenced flowering time.
Now, when a Wisley plant trial proves especially successful or especially interesting - as this one was - the enterprising staff of the Botany Department and the Trials Office get together, with input from the judges, to produce a report: a Plant Bulletin. There's a complete list of bulletins on the RHS website. The 16 page, full colour Hydrangea paniculata bulletin is just out.
Not only does it reveal and illustrate the results of those pruning trials but all 47 varieties are described and illustrated with AGM winners illustrated at two stages of their flowering season. Packed with useful information, it's available as a FREE download.