Coming up: Roses!
Summer is showtime at the Lady Norward Rose Garden in Wellington’s Botanic Garden and despite the challenging wet winter and spring which, like many gardens, left this one with much higher than normal soil water levels, the show promises to be gorgeous.
Clare Shearman, Plant Collection Team Manager says they’ve been trialing a new seaweed-based organic product on the roses for the last 5 years, with some interesting results. Normally a product trial is a three-year exercise, but with the interruption of Covid and its unpredictable journey, the decision was made to leave the trial running for 5 years. Clare says the longer trial period threw up an interesting result in this garden because it showed that over a longer time, these roses preferred a slow-release fertiliser, as opposed to the quick ‘sugar rush’ from the trial product. The latter has its benefits in a small home garden if you want immediate results, but with a large rose garden such as this – there are 140 ‘beds’ including those around the perimeter – the management team is now certain that the best results are derived from a slow-release fertiliser.
At the moment, the team are using a Dalton organic slow-release pellet which is top-dressed before mulch is applied. Application is done in September. The mulch of course ensures soil moisture is retained, weeds are kept down and the soil is conditioned. Only organic applications are used in this garden and the roses are not treated for pests and disease.
The roses certainly come under close scrutiny by garden staff and data is collected constantly from robust assessments. Relying on memory of previous years’ performance is not, well, reliable! As well as the usual visual record on how a plant is performing, the soil is monitored via 4 in-ground sensors – one in each quadrant – which provide information about water content, temperature and soil salinity. The data is collected via wifi and this new technology is proving to be an invaluable tool. For example, it allows Clare to receive a beep on her phone if the water content in the soil drops below 20%. Incidentally, the garden’s optimal soil water content is between 21-40%, and the soil PH for roses should be between 6-6.5.
With some of the roses in the Lady Norward Rose Garden as old as 70 years, there is a lot at stake to keep the plants in tip top condition. While the oldies are treasures, Clare says the management team is not afraid of replacing any which are not performing. This means checking the rose’s status on a point score system. The points are awarded on the basis of a rose’s appeal (its look, smell and habit) as well as on how it performs under all conditions and its position in the garden. Care has to be taken to keep the ideal mix of colours. If a rose variety drops on the sliding points table, a decision is made to ‘let it go’. Normally this involves replacing the whole bed which is dug up using a small digger rather than manually. This process creates an opportunity for drainage to be laid. The garden is a sunken garden after all and has a flatbed substratum. With the unpredictable climate we now have, drain laying is seen as a sensible precautionary measure.
Do visit the Lady Norward Rose Garden when you are next in Wellington. The reward is yours to take.