Posted: 29/09/2015 at 00:15
My last garden in Harrow and this one in Belgium both have mainly north facing gardens. Harrow had acid clay soil so lots of compost went in and we grew rhododendrons, azaleas, roses and a wide range of perennials. The shadiest bit was up by the house but the bottom of the garden had full sun in summer. I expect your sister's is the same.
This garden is alkaline loam on a clay sub soil so clematis do very well in shade and sun. I can't grow ericaceous plants but buddleias, roses, conifers, mahonia, weigelias, Japanese maples, sambucus, choisya, physocarpus, colourful stemmed cornus, philadelphus and so on do very well.
The list of perennials that love it here is huge but in the heaviest shade up by the house I grow hostas, Japanese anemones, filipendula, primulas, ligularias, lily of the valley, astilbes, astilboides, fuchsias (in pots and baskets), snowdrops and miniature daffs.
Hardy geraniums, dicentras, pulmonarias, brunneras, persicarias for dappled shade and then an almost endless choice for the sunnier parts depending on colour preferences.
Use well rotted garden compost and manure or spent compost or bought in soil conditioners to improve the drainage in the clay before planting. Save the microrhizal stuff for roots at planting time.