Government of New Brunswick

Agdex No. 282.21

Herbaceous perennials are plants having stems and leaves that die in late fall but whose roots live for many years.


Traditionally perennial gardens have been placed at the side or back of a property, but newer gardens can take advantage of areas around a carport or the wings of a house. Many perennial plants are tall and are easily damaged by strong winds. A fence or hedge is an effective windbreak while allowing the adequate air circulation necessary to prevent mildew and other diseases.

Many perennials are adapted to various soil and light conditions but to allow for the greatest choice in border plants, average garden soil receiving at least a half day of sunshine is ideal. Well drained soil is essential for the survival of a perennial garden.

Soil Preparation

Preparation of the soil in a perennial border should be thorough to provide the best growing environment for many years. Dig the soil to a depth of at least 30 cm, and incorporate well rotted manure, or compost to improve the soil structure. A complete fertilizer 5-20-20 or 5-20-10 at 1.0 to 1.5 kg/10m2 can be added at this time if necessary.

A soil test available through the New Brunswick Department of Agriculture will give lime and fertilizer recommendations for a specific soil.

Planning the Border

The design of the border and the habit, texture, form and colour of the plants give a perennial garden its character.

To begin a perennial border make a scale drawing of the site. On this drawing, plan the placement of each plant in the border and indicate its height, colour and bloom time. Taller plants usually form the back of the border and lower growing plants are used in the foreground. To achieve a natural effect, put some taller species in the center of the garden and some medium height species in the foreground. Try to develop a unified look with pleasing contrasts using plants of different colours. White flowers can effectively separate vibrant colours while giving the border continuity. Massed colours can be repeated throughout the garden very effectively.

Most perennial borders are planned to have colour from early spring to frost. This can be accomplished by first choosing plants that bloom consecutively through the season and then arranging other plants around this foundation.

Planting and Care

Most perennials are best planted in the spring. While planting do not allow the roots to dry out. Note any special planting requirements for each species used in the border. Annual plants can be planted to fill in gaps while the perennials are developing.

Check each spring for plants that have been heaved by the frost. Press these plants gently back into the soil to avoid unnecessary losses. A light dressing of well rotted manure or compost can be applied in spring to improve growth. Avoid a heavy fertilizer application after midsummer as this produces soft growth prone to winter injury.

Supplemental watering needs vary with the plant, the soil and the weather conditions. When soil is dry, water thoroughly about once a week as light, frequent watering encourages shallow root growth.

Space plants properly when planting; this ensures a good display with a minimum of attention. Occasionally it will be necessary to divide plants when the clumps get too large. To divide, dig the plant up and gently pull apart or cut the clump, saving the newer growth. Generally spring blooming plants are divided in the fall and later blooming plants are divided in the spring. Exceptions to the rule include: Irises(divide early August), poppies (August) and peonies (early September).

Tall perennials that require support should be staked and tied to allow the plant some movement. Tomato cages and peony rings can also be used for plant supports.

Cutting off all faded blooms maintains a tidy garden and keeps plants from setting seed thereby extending the bloom period. Plants should be cut off close to the ground once the foliage has been killed by the frost. Remove all foliage in the bed and burn it to prevent disease. Once the ground is frozen, a mulch of brush or straw may be placed among the plants to hold the snow and prevent winter thawing.