Herbaceous perennials FAQs

What exactly is a herbaceous border, and how should it be planted?

Traditionally, a herbaceous border was at least 3 m (10 ft) wide and about 10 m (35 ft) long, usually backed by an evergreen hedge, and planted entirely with herbaceous perennials. As this is impractical today in most gardens, herbaceous borders tend to be much smaller and of irregular shape to give more interest. They are usually planted with clusters of each type of plant, in groups of three to five; the tallest are at the back and the lowest at the front. The clumps of plants are intermingled to a certain extent to give an informal effect.

The plants are selected to harmonise in terms of colour and give different times of flowering, so there is always something of interest in the border in the spring, summer, and autumn. Which herbaceous plants are selected from the huge number available is a matter of personal taste and colour harmonies. Plant breeders have recently introduced a wide range of low-growing varieties suitable for the smaller border.

How must I prepare the ground to make a new herbaceous border?

As your plants are likely to be in the ground for a long time, it pays to prepare the soil thoroughly. Remove all weeds, especially the perennial types with deep roots, by digging, hoeing, or with a suitable weedkiller. Then fork the soil to a depth of at least 150 mm (6 in), adding humus-forming matter such as well-rotted manure or compost, rotted bark, granulated peat, or hop manure. Lime may also be needed if the soil is very acid (peaty) or in generally very poor condition. It should be applied in autumn or spring, one month before planting or adding humus-forming matter, or two or three months after manuring (lime and manure must never be applied at the same time). If possible, leave the freshly dug soil for a couple of months to allow it to settle, then scatter a general-purpose fertiliser over it and rake the ground to give a reasonably crumbly surface suitable for planting.

Can you recommend a planting plan for my herbaceous border?

Using a sheet of graph paper draw on to it (to scale) the shape of the border. Then select your plants from a catalogue or book which not only describes the plants but also gives an indication of their height and spread. Allow for the plants to be grouped in clumps of three or five and draw a rough semi-circle on the plan for each clump, giving the plants the spacing they will ultimately require. The very tall plants will go at the back of the border (or centre if it is an island bed); the heights of the remaining subjects are gradually reduced until you are left with the low-growing edging plants.

If you use a set of colour crayons to draw the semi-circles, it will help to give you an idea of a colour scheme. Write into each semi-circle the name of the plant and its period of flowering, so that you can make sure that you will not be left with large non-flowering areas at any time. If you plan in this way, you will buy the right number of plants in the colours you like best and will be able to place them in the correct positions in the ground.

Are herbaceous plants fussy about whether the soil is acid or alkaline?

Nearly all herbaceous perennials grow well in most soils, provided they are neither very acid nor very alkaline. By manuring and liming regularly, the soil can usually be kept at a fairly neutral pH , while applications of fertiliser will supply the nutrients the plants need.

When is the best time to plant herbaceous plants, and how are they set out?

The best time is spring or autumn, although those grown in containers can be planted at any time of year provided they are kept well watered. If you buy by mail order, the nurseryman will send you the plants at the right time for planting, although the roots will probably have little or no soil on them. If you cannot get them planted on arrival, store them in a cool place in damp peat or put them in a trench in the garden. However, do try to plant them out as quickly as possible provided that the ground is workable. If the plants seem dry on arrival, soak the roots in water for 24 hours; if any are damaged in transit, let the nurseryman know immediately.

Planting is best done with a trowel. Set the plants in holes large enough to accommodate the roots without cramping them. Work from the back of the border (or centre of an island bed), spacing the plants to suit their final growing size and according to your planting plan. Always plant to the same depth as the soil mark on the stems. Hoe carefully to remove footmarks, and water in the plants with a thorough but gentle sprinkling. Do not forget to label each clump of plants.

As the border may look a little empty while the herbaceous perennials are maturing, fill the spaces temporarily with bulbs, bedding plants, or annuals to give summer colour—but be careful not to crowd out the perennials.

Is it better to buy herbaceous plants from a garden centre or (by mail-order) from a nursery?

The answer depends really on what you want. If you need an ‘instant’ border and are not too fussy about which particular species or varieties you grow, good well-established container-grown plants from a garden centre can be set out at any time during the season. The plants must be carefully and regularly watered if they are planted during the summer. This will get them established and encourage them to make new growth.

The advantage of buying by mail-order is that you generally have a much larger choice of plants, species, and varieties from which to choose, and can therefore create a more interesting final effect; many nurseries have made a name for themselves by specialising in a particular range of plants. The main disadvantage of mail-order is that you are generally confined to plants suitable for spring or autumn planting. There is generally little difference between the two methods of buying in terms of cost.

My garden is somewhat exposed to winds. How can I prevent the stems of my perennials from breaking?

It is always advisable, even in a sheltered garden, to stake tall or weak-growing plants. Single-stemmed plants, such as delphiniums, should each have a bamboo cane and be tied with twine at intervals as they grow. Less tall but floppy-growing plants can be supported with ‘pea sticks’ (tree and hedge trimmings) of different heights, so that the plants grow through the twigs and support themselves. Short-growing floppy plants will require only the twiggy top-growths of those pea-sticks.

Alternatively, a number of different kinds of proprietary plant supports are available, usually made of wire and often in various shapes for different plants. It is best to put the plant supports in position in spring and remove them in autumn.

If your garden is so exposed that these regular types of supports are inadequate, grow the lower-growing or dwarf varieties of tall plants; many have been introduced recently and are just as effective as their taller counterparts.

If it is at all possible, create windbreaks with fencing and hedges. This will not only help to protect your plants but make the garden a pleasanter place to sit in. If high winds are the norm, a fence should act as a filter rather than as a barrier. Not only is a solid fence likely to be blown down; it is also apt (like a wall) to set up turbulence on the lee-side, and so cause as much havoc in beds and borders as direct winds.

How can I get rid of the weeds in my new herbaceous border?

The real answer is to keep hoeing, because it is vital to prevent annual weeds from seeding. Deep-rooted perennial weeds, however, such as docks and dandelions, should have their entire roots taken out; a long-bladed knife is a good tool for this job. It is possible in theory to use a systemic weedkiller by painting the solution on to the weeds with a brush, but this is time-consuming and great care is needed to keep the chemical away from the cultivated plants.

Once the ground is clear of weeds, and when the soil is moist, apply a 50 mm (2 in) layer of mulch ; this will help to suppress the weeds. 219

Is it necessary to water herbaceous-plant borders?

All plants benefit to a greater or lesser degree from artificial watering during extended dry periods, and herbaceous plants are no exception. Whatever method of applying the water is used— sprinkler, hose, or watering can— make a thorough job of it every few days if necessary, so that the water reaches a depth of 300 mm (12 in) for large plants and 150 mm (6 in) for smaller ones. Merely sprinkling the plants does more harm than good: if regularly practised it will encourage the parched roots to grow nearer the surface in search of moisture.

Do herbaceous perennials need dead-heading?

Yes: to keep the border looking tidy, to prevent plants wasting their energies on seed production, and to encourage them to flower again (unless, of course, you require the seeds for propagation or the seed heads for decoration).

Use secateurs, a sharp knife, finger and thumb, or a flower-gathering type of implement for dead-heading most types of plants; shears should be used on edging or ground-cover plants such as aubrieta, perennial alyssum, and similar mat-forming subjects whose heads are too small and too numerous to remove individually.

Should I feed the plants in my herbaceous border?

Yes: apply fertilisers at least twice a year—a general one in the spring and bonemeal in the autumn. Both should be applied at the rate recommended by the manufacturer, and then hoed or forked into the soil. Booster feeds of a liquid fertiliser are often beneficial during the growing season.

To keep the soil in good heart, fork in mulching materials or manure each autumn; apply lime if the soil is sour, badly drained, or very peaty.

My herbaceous border tends to look a mess in the autumn. What’s the best way to tidy it up?

After the first autumn frosts, cut back the stems of all but evergreen or winter-flowering herbaceous plants to about 100 mm (4 in) above the ground. Remove, clean, and store plant supports. Remove all weeds, then lightly fork over the border to a depth of 100 mm (4 in) to loosen the soil and incorporate the early summer mulch. When doing this take care not to damage the plants’ roots. Leave the soil surface rough. Ensure the plant labels are left in position. Manure or lime can be added (but not both at the same time) while you are forking and worked-in later.

I have read that it is necessary to fork over the herbaceous border in the spring. Why is this?

For the same reasons, in the main, that it should be forked over in the autumn: to aerate the top soil, to incorporate manure or lime, to remove footmarks after putting plant supports in position, to mix in a general fertiliser, and to remove weeds. After this, the ground is usually ready for mulching.

How (and when) should I increase my herbaceous perennials?

Most herbaceous plants can be increased by division in mild weather in autumn (after cutting back) or in early spring, when they are dormant (that is, not in active growth). Dig up the plants and, if they have a matted root system, pull this apart by hand, or split them by levering two garden forks back to back to break the clump into pieces. Replant the new outside pieces of root and discard the older inner portions.

If the roots are tuberous or rhizomatous—for instance, iris, Solomon’s seal (Polygonatum), bergenia, bergamot (Monarda), peony (Paeonia), day lily (Hemerocallis), or anemone—lift them in spring and cut them into sections with a sharp knife, so that each has growth buds and roots.

Herbaceous plants can also be increased by basal cuttings, tip cuttings, root cuttings, and some are grown from seed. Layering is sometimes used during the summer, especially for border carnations (Dianthus).

I have ‘inherited’ a very overgrown and weedy herbaceous border. What do you suggest I do to renovate it?

Regretfully, the only really practical answer is virtually to start from scratch. The border is probably best dealt with in sections. Dig up all the plants and weeds, get rid of the latter, divide the former if you want to keep them, fork the bed, adding compost, lime (if needed), and fertiliser, and then replant. To keep herbaceous plants happy and in good health, this sort of operation should be undertaken about every three to five years and is well worth the effort involved.

Are there any herbaceous plants that flower during the winter?

Regrettably, very few. Four that are useful for this purpose, however, are: kaffir lily (Schizostylis coccineum), from September to November; stylosa iris (Iris unguicularis), from October to March, Christmas rose (Helleborus niger) from January to

February, and Bergenia ‘Silver Light’ from February to March. Putting cloches over the last three will encourage earlier flowering and protect the blooms from severe winter weather.

In my exposed garden I find that many of my favourite plants, such as bear’s breeches (Acanthus), African lily (Agapanthus), Peruvian lily (Alstroemeria), red-hot poker (Kniphofia), penstemon, cape figwort (Phygelius), and kaffir lily (Schizostylis), rarely survive our cold winters. Can I protect them in situ or do they have to be lifted and kept in a frost-free place?

Such plants can usually be left in place in the ground provided they are protected with a 50-100 mm (2-4 in) covering of leaves, straw, or bracken from late autumn to mid- to late spring. Fix the protective material in place with twiggy sticks or pegged-down netting.

Sorry, comments are closed for this post.