Plenty of blue in the August garden
CONSIDERING that August is the hottest month of the year it’s surprising how many cold colours, blues in particular, are prevalent in the garden at the moment, though they have been sadly lacking in the August sky unfortunately.
Blue is a colour I am fond of in the garden so needless to say I am quite happy at this time of year when so many of my favourite plants are in flower. Agapanthus, the African lily, are so common place these days it is easy to take them for granted. In our climate these tough, resilient, dramatic plants ask nothing more than a bit of sunshine to perform with super showy blue or white flowers. They come in evergreen or deciduous varieties with the later being hardier so more suitable for in land areas.
That said in cold winters even the evergreens can lose their leaves. I leave the flower heads on mine as they are decorative right up to Christmas and seem to cause no problem for the plant in flowering next year. If it is dry when they are flowering give them a water as this does help the bulbs below ground to generate some energy. Varieties Arctic Star which is white, African Skies a blue and Black Pantha which has a very dark blue bud opening dark blue in flower are recommended.
Lavender is always on everyones wish list and I’m no exception. There are two main types of lavender we grow in Ireland, Lavendula angustifolia which is short and compact flowering at 30 to 40 centimetres and Lavendula x intermedia taller flowering at 60 to 90 centimetres. Both love hot, dry, poor soils. Wet heavy ground is the absolute enemy of lavender.
It is important to clip back lavender every year as this keeps the plant compact and increases its life span. Angustifolia types should be clipped hard but into live foliage growth in early September. Intermedia types should be treated the same only a couple of weeks later. Prune back at this time even if there are still flowers on them as they need time to reshoot before winter. Failing to prune annually will cause your plants to become very open and leggy within a couple of years.
Another plant that is a fuzz of blue at present, and one which you’d be forgiven for mistaking for a lavender, at least at a distance, is Perovskia. Commonly called Russian sage. This lovely sub shrub requires the same conditions as a lavender but is treated very differently when pruning. Wait until the spring just as some leaf growth is begining to show around mid April then cut it back hard to a little woody framework 20 centimetres high. This again should be done annually. Perovskia ‘Blue Spire’ flowers at 90 centimetres to a metre high, ‘Little Spire’ is more compact at 75 centimetres and ‘Lacey Blue smaller again at 60 centimetres.
Also from a similar sub shrub cateagory is Caryopteris also called Blue Spiraea. Again quite lavender like it is a long late summer blue flowerer with the same soil requirements of both lavender and Perovskia but is pruned like the Perovskia. The best and most common variety is called ‘Heavenly Blue’ flowering at 60 to 80 centimetres high. There are yellow leaved varieties available but for me these are quite unattractive and ill looking.
Finally the piercing blue of an other sub shrub the Ceratostigmas or hardy plumbagos. These are beautifully undestated charming little plants generally available in two species Ceratostigma willmottianum and P. griffthii. Again hot dry conditions are required to get the best out of these plants and with all the plants mentioned here, with the exception of Agapanthus, poor starved soils improve their flowering.
The stunning small blue flowers are followed by red autumn colours. Pruning can be left until spring but is less essential annually than with the other sub shrubs covered here. You can cut them hard to the ground to regenerate or allow them to get larger and just thin out some of the old flowering wood.