This Month in the Garden – September 2019 with Derek Cox

Shrubby Hydrangea’s are at their best during late July, August and September, and for a number of years while on holiday in North Devon we visited Marwood gardens, not only for its glorious water features, but also to see large shrubs of Hydrangea’s growing on the open hillside. They are usually not happy in exposed positions, but when talking to a gardener on the site I found out there were a number of springs beneath the soil and these kept the Hydrangea’s moist during the growing season. I must admit that I struggle with most mop head and lace cap Hydrangea’s. I grow them in a shady border facing North West and even then, unless during the growing season I give them around two gallons of water each day the leaves curl and the flowers look insipid.
Here I must say that during late winter I always give my plants a mulch of old garden compost, this not only feeds the plants but also does contribute to helping retain water. Mop head and lace cap Hydrangea’s flower on their previous year’s growth and should only be pruned immediately after the flowers have faded.
Hydrangea paniculata and arborescens cultivars flower on their current year’s growth and can be cut down to within six inches of the ground during March.
The two small troughs on my terrace that contain red Begonia’s have looked outstanding for the last two months and unless we get any early frosts they will continue to flower, as they did last year, until the end of October. The dense mass of small red flowers almost obscure the plants reddish-bronze leaves, and these hang over the edge of each trough.
Plants which fill containers will shed most of the rain that falls so I thoroughly water the troughs every week to make sure they stay in flower.
Most of my Alstroemeria’s have finished flowering, accepting the variety ‘Summer Break’, which although repotted last spring into a 15 litre pot started to flower in July and still has so many buds on the stems that I can see it will be in flower in October. I grow this standing outdoors and like my entire container grown plants it is given a feed of tomato fertilizer once a week.
I have grown Caryopteris clandanensis ‘Heavenly Blue’ in a shady border for over 15 years. This forms a low growing shrub with grey-lavender scented foliage and panicles of blue flowers during August and September. Caryopteris flower on its current year’s growth so I prune it back during March to keep it neat and tidy. Most gardening books will tell you that Caryopteris are best grown in full sun, but in my sandy loam it still puts on a lovely show. This year a gold leaf seedling of ‘Heavenly Blue’ appeared at the end of my bog garden, it has lovely foliage that resembles that of the variety ‘Worcester Gold’ I shall have to wait until it flowers next year to see if it is different and worth introducing into the trade.
When I first planted Zauschneria californica ‘Dublin’ in the raised bed on the South side of my greenhouse little did I know how rapidly it would spread and sucker through the ground. During August and September this is massed with orange-red trumpet shaped flowers and looks outstanding, but it has now completely filled the bed and in doing so has killed many alpines.
There are a few Sempervivums still making a go of it by growing on top of the retaining wall, but even these are pulled up by blackbirds in search of insects. I love my plants, but also the birds so it is a constant battle of me replanting the Sempervivums and the blackbirds pulling them out. My ‘St George’ runner beans are still producing a good crop of beans, but my climbing French bean ‘Golden Gate’ only starts to produce its flat yellow beans during late August.