The Christchurch Botanic Gardens

Information Sheets

Herbaceous Border

The herbaceous border is a familiar symbol of the English country garden. These borders are usually large in scale with their sheer size creating a dramatic and spectacular scene at the height of summer.

The Christchurch Botanic Gardens Herbaceous Border has been situated in its approximate vicinity since 1921. The present border was constructed in 1926 and divided into two sections in 1934. The existing border is now one of the few such gardens remaining within a public garden in New Zealand.

A herbaceous border is a collection of herbaceous perennial plants, grouped closely together to create a dynamic effect. Herbaceous perennials are a large group of garden plants that are botanically defined as soft stemmed plants that lack secondary (woody) thickening. Their common characteristic is that their roots persist from year to year, surviving each winter as underground storage organs such as bulbs, corms, rhizomes, stem or root tubers. Stems and leaves of some may remain, although in most instances the top growth dies back to ground level each winter.

The diversity of herbaceous perennials is vast and there are suitable species, varieties and cultivars for almost any garden situation, be it intense sun or deep shade. Many are grown for use as cut or dried flowers while others are utilised for their attractive foliage. They play a major role in landscaping and are frequently incorporated in mixed flower and shrub borders, summer bedding displays, container gardens, specialist areas such as rock, water or wildflower gardens with some also being used for ground and bank coverings.

The design and planning of the Herbaceous Border

The Herbaceous Border at the Christchurch Botanic Gardens is ideally situated, having a neutral back drop of mature trees and shrubs. The plantings to the north of the border provide the necessary shelter from the wind but are far enough away to prevent excessive shading and root competition. A wide range of plants and heights are made possible because of the length and width of the border. The soil in this area is a light, fertile, well drained loam with a near to neutral pH.

During the summer months plants are evaluated on their performance in the border. Alterations and amendments to the plan are then carried out during winter. The five main points considered when planning planting positions are colour, height, flowering period, form and texture. Hardiness and suitability for the growing conditions are also assessed.

Colour in the border is used in a way to ensure a sense of unity. Plants are usually grouped en masse in large drifts. Each group of plants is carefuly chosen so as not to clash with its neighbour and therefore presents a unified picture. Dominant colour spread throughout the border gives a feeling of repetition and rhythm. As various plant groups are dominant at certain times, colour will often look after itself as colours within these groups are usually harmonious. White flowered plants are often used effectively in this border as links between various colours.

Plants are also arranged according to height and are graduated with low plantings to the front and taller ones to the rear of the border. Some taller plantings are occasionally brought forward and lower ones set back to prevent a regimented appearance. A graduated stepping down of heights with some groups rising above others creates a series of hills and valleys that add interest to the plantings.

Records are kept concerning length of time a particular plant will take to reach flowering stage and the period of time it will continue to flower. These records are used to space groups of early or late flowering perennials regularly throughout the border, helping to prevent large flowerless areas.

Plants with differing forms and textures are used where possible as they provide interesting contrasts and visual appeal. Many herbaceous perennials in this border are worthy of growing for their foliage alone.

There are many factors considered when choosing plants that will be suitable for growing in the Herbaceous Border. The ability to withstand hot, dry, windy conditions, frost hardiness and growth rate are just some of these.

The maintenance and care of the Herbaceous Border

This border is one of a number of high maintenance areas that require much attention throughout the year.

As most of the plants in the Herbaceous Border are multi-crowned perennials, division is the simplest method of propagation. Lifting and dividing of the border or sections of it depends on the size and growth rates of the plants or plant groups. The selected plants or plant groups are usually lifted, divided and replanted each year during August.

Plants are lifted from the ground and pulled apart, either by hand or divided by using two forks placed back to back. The tines are plunged deep into the centre of the crown and forced apart by pushing the two fork handles together, then apart. This process is repeated until the clump is separated into acceptably sized pieces. Only the young vigorous outer growths of the crowns are replanted after the roots and any top growth has been trimmed.

After removing the plants from the border, the areas to be replanted are cultivated to a depth of approximately 150mm. If the soil is lacking in organic matter, compost is incorporated before the area is cultivated. Prior to planting the soil is lightly consolidated by heeling, the surface raked to a fine state and lightly mounded towards the centre of the border to aid in drainage.

Working from a prepared plan, areas are defined to indicate where each plant or plant group is to be placed in the border. Planting distances depend on the size of the plants, their rate of growth and the length of time the plants will be in their positions. Planting holes made with a trowel or spade are wide and deep enough to take the roots of the clump comfortably so that the crown of the plant is just showing through the soil surface when planting is complete. Exceptions to this rule are rhizomes which are planted at surface level and bulbs which are planted to a depth of twice their diameter.

It is at this time that plant material grown on in the nursery either from seed, cuttings, layers, or as purchased plants are added to the border's collection. Replacement plants and new introductions including a wide range of interesting, unusual and rare perennials are continually being sourced from New Zealand and overseas catalogues.

After planting a mulch of fine bark is applied to the border to a depth of approximately 20mm. This improves the physical condition of the soil by supplying plants with nutrients as it decomposes as well as helping smother weeds and conserving moisture. A light forking of the border throughout the year allows air and moisture to penetrate to the roots of the plants while at the same time exposing unwanted weeds.

Few sprays are used for pest and disease control in the border with natural sprays now used to combat any serious infestations that may occur. An application of a general fertiliser is made in the spring and summer to encourage growth at these times of the year. Overhead sprinklers are used during the early morning to irrigate various sections of the border when necessary.

The weakest shoots on some plants are lightly thinned out during spring to encourage strong stem formation and large flower heads. Herbaceous perennials that have a naturally floppy habit or ones that become top heavy when in flower are given support. Neutrally coloured stakes are put in position in late spring before growth is too advanced. These stakes are put in to a depth that will be lower than the ultimate height of the plant, therefore inconspicuous when flowering begins. Unobtrusive ties that will not damage plant stems are tied around stakes and criss crossed through the plant group for extra support. Taller plantings will often require two tiers of ties.

Spent flowers are removed regularly not only for appearance but to encourage further flowering, thus prolonging the flowering season. Dead or dying foliage on evergreen and deciduous herbaceous perennials is removed during the autumn and early winter as the plants start to die back. As well as for aesthetic reasons this helps to reduce the incidence of pest and disease build up.

New methods and practices associated with the herbaceous border are constantly being trialed and evaluated. An example of this is the trial of large wire frames used to support some of the taller plant groups.

A list of common perennials grown in the Herbaceous Border is available here.