Traditionally Autumn and Spring have been considered the best times of year to undertake new planting, including the transplanting of existing material. However, there has been a trend over recent years where Spring has been dry and not good for successful planting and establishment. Consequently, we are advocating as much autumn planting as possible. This is also the approach that Kew Botanic Gardens are taking along with Monty Don.
There are some exceptions, however. I have some young shrubby salvias that once established will prove hardy. But as small youngsters I am inclined to grow them on and plant them out next April when normally the worst of the frosts have finished. As a guide to dividing perennials, spring flowering types are divided in the autumn while late summer ones are divided in the Spring. This is partly to avoid dividing them when they are in full flower. As I write this in October the Michaelmas-daisies are in full flower, so they will be left alone, the likes of hardy geraniums on the other hand, are fair game. There are occasions when you simply need to get things done. If we really had to, we could divide a Michaelmas-daisy in full flower. To give the plant the best chance we would have to cut it right back to reduce the shock and focus its energy into re-establishing rather than trying to continue flowering. In the case of ornamental grasses, it is best to divide them in the Spring once they are in active growth. If you divide them in the autumn when they are going dormant, there is a chance they will rot and die. Being in active growth means any cuts and wounds made will heal fast with the plant quickly re-establishing.
At the moment we have some areas that are left bare and are liable to become a carpet of weeds. To get the ground covered up and stop weed seed germinating we are attempting the momentous task of dividing and transplanting as much ground cover as possible. Geranium macrorrhizum and Phlomis russeliana are well established in the garden and are tolerant of dry and shady conditions. This makes them useful for underplanting shrubs. To keep things simple, we will tend to plant in groups of seven or more to form drifts. This makes things easier for those with less plant knowledge. If the plants were more mixed up it would be harder for them to know what should and what should not be there. It is also easier to maintain. A whole drift can be cut back in one go and saves having to hunt down individual specimens. Large drifts can be made more interesting by using dot plants. Dot plants tend to be the larger species in the mix with a more architectural shape.
Dividing existing plants has the advantage of making what you have go further. It also saves having to buy in new stock. In some cases, it is possible to turn 1m2 of say a geranium into 3m2 by lifting and diving into smaller chunks. For a viable plant each division should have at least three to seven shoots compete with a section of the crown and roots. For quicker establishment I tend to make the divisions about the same width as my spades blade. In some cases, plants tend to fall apart into individual rhizomes. With the Geranium macrorrhizum, I have dug over the new planting site then made shallow trenches, laid out the Geranium rhizomes along the length of the trench, then back filled with soil covering the rhizomes with the leaves still protruding.
To increase the variety of plants we grow at Whatton House and to extend the season of interest we are planning to buy in some new material. But mostly we intend to work with what we already have. The result of this should better presentation and something that is easier to manage. As an added benefit of all this digging there is little need for us to go to the gym.
William Stanger of Four Winds Horticulture is a local Garden Consultant and international writer. He is advising Whatton House on the garden’s regeneration. He has worked at various gardens in the U.K and New Zealand including The Savill Garden and Dunedin Botanic Garden. He has a M.A. in Historic Designed Landscapes and a BSc Hons in Green Space Management.
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