As the textbooks will tell you, herbaceous perennials are plants which die down every winter and produce newand foliage each spring. This standard definition does indeed apply to most of the herbaceous perennials we grow in the garden, but you can find exceptions to both halves of this over-simple description.
First of all, not all herbaceous perennials die down in winter. From tiny Saxifrages hugging the earth to the large archingof Pampas Grass you will find evergreens in a variety of shapes and sizes – Brunnera, Helleborus, , , Stachys and Tiarella are examples. Your border should contain some of these evergreen types if you wish to avoid a completely bare look during the depths of winter.
Secondly, the statement that they pop up afresh every spring is also not always true. Some types are not completely hardy and so are liable to die in severe winters, and several others which are completely hardy are not long-lived even when the growing conditions are ideal., Anchusa and Perennial Flax are well-known examples of plants with a strictly limited life span. Nearly all of the rest will go on year after year, but many require lifting and dividing every few years to prevent deterioration. There is just a small group of plants to which the word ‘perennial’ really applies – plants like Acanthus, Helleborus and Paeonies which should be left alone so that they can continue to flourish without disturbance for decades.
An enormous number of plants are classified as herbaceous perennials, and the ones which grow to a foot or more are termed border perennials, because the herbaceous and the mixed borders are their traditional homes. To see border perennials at their classical best, look at a herbaceous border in midsummer.
Towards the end of the nineteenth century there was a violent swing away from the regimented rows of bedding plants in the flower beds of the mid Victorians. Under the influence of William Robinson and Gertrude Jekyll the herbaceous border was born, and all sorts of rules were developed. A backdrop of a hedge (preferably Yew) or weathered brick was essential and border perennials were planted in, carefully tiered with the tallest specimens at the back and the low-growing perennials at the front to divide the border from the lawn. Plans were carefully drawn before planting took place – colour clashes were avoided like the plague, neighbouring plants had to bloom in sequence, contrasting flower forms were put next to each other to add interest, and so on. The length had to be impressive and the width no less than 9 ft – in its de-luxe form two parallel borders faced each other and were separated by a broad path of closely-mown turf.
The herbaceous border is a thing to see – you will find splendid examples at Wisley, Hampton Court, Gt. Dixter and many other grand gardens in Britain. It is a thing to see but not to make these days. It requires a great deal of space and attention, and it can be seen from only one side. The screening hedge cuts down both light and air circulation so that the back row leans forward unless it is carefully and constantly staked, and even with loving and skilful care the best of borders have a barren look for part of the year.
If you want to have an area just for border perennials then make an island bed instead . Here the plants can be seen from all sides and there is no shading effect from surrounding walls or hedges. The tallest plants are set in the middle and the not-so-strict rule is that their height should be no more than half the width of the bed. You can see excellent examples at Bressingham Gardens in Norfolk – the birthplace of the island bed.
For the average-sized garden the mixed border is the answer. This owes as much to the idea of the old cottage garden as it does to the principles of herbaceous and shrub borders. The basic concept is to have some colour all year round -choose from where you will amongst the complete range of garden plants.with evergreen and provide a woody and colourful framework – within this setting the border perennials are planted in of three or five – avoid the spotty effect resulting from growing single isolated specimens. Plant and bulbs to fill the bare spots close to the front of the border. The will provide a summer-long floral and bulbs will bring the border to life in late winter or early spring. There are a few rules to ensure success -get rid of perennial weeds before planting a mixed border and choose the smaller and sturdier modern varieties of border perennials so as to reduce the need for staking. Above all, check in the A-Z guides that the plants you have picked are suitable for the conditions.