Cultivating Annuals and Biennials

Annuals are plants which complete their life cycle from small dormant seeds through germination, development, flowering and harvesting all within the space of a year. Although their life span is thus short, measured against herbaceous perennials, shrubs and trees, they make up for this with a prodigality of blossom unsurpassed by any other group of plants.

Their colourful, long-blooming qualities render them invaluable wherever quick colour is desired. They are particularly useful for new gardens the first season, hiding the bare soil beneath a carpet of flowers. In later years or in established gardens the potentialities are even greater; their uses extending to window boxes, hanging baskets and containers of all description as well as beds and borders.

Biennials are plants which take two years to complete their life cycle. Seed sown one season develops a rosette of leaves that year and flowers and fruits the next. Usually the seed of such plants is sown outside — in shallow drills in late spring. Later the seedlings are pricked out in nursery beds prior to being bedded out in the autumn. While many biennials are mainly used for bedding purposes (for example wallflowers and forget-me-nots) others fit into the annual or mixed border if used during their second season. Canterbury bells and sweet williams are frequently used in this way.

Again, a number of perennials often make better plants or are less subject to disease when treated as annuals or biennials. Antirrhinums, for instance, are almost invariably treated as annuals and polyanthus, hollyhocks and double daisies as biennials.

biennial sweet william

Another advantage of using annuals and biennials is economic. They are easy to grow and seed is cheaper to purchase than plants. The hardy annuals may be sown where they are to flower and some of them start to bloom within two months of sowing. Half-hardy annuals have to be raised under glass and planted outside when all risk of frost is past. Their use thus presupposes the possession of a frost-free — or heated — frame or greenhouse.

Preparing the Ground

Although annuals have worldwide distribution, many of those which have become most popular with gardeners appear to be native to central and South America and South Africa. Their brilliant colourings seem in some way to be linked with the sunshine of their native lands. Background knowledge of indigenous conditions often provides clues as to treatment and generally speaking monocarpic plants do best in good soil and open sunny situations. With few exceptions flower beds solely devoted to annuals, window boxes, or groups of annuals in mixed borders should be sited in open positions and away from trees or hedges which can draw up the stems.

For best results the ground should be prepared in autumn; cleared of weeds and deeply dug. Organic material should be incorporated through the top 12 in. to provide a reservoir of food and hold moisture in summer, but this must be well rotted. Farmyard manure, garden compost, leafmould and moist peat are all suitable. When this rots down to friable humus any type of soil, regardless of its original nature, will benefit in tilth and texture.

Because of their adaptability there is a common misconception that annuals do best in poor soil. This is not so. They will grow in a fashion on poor land, but there is no comparison between the resultant plants and those raised under more favourable conditions.

If biennials are to be good, it is equally important that they too be grown in good soil: Stocks and Canterbury bells particularly require fertile land. Others, such as foxgloves, honesty and meconopsis, need moist soil but prefer light shade in summer.

Once the border is adequately prepared hardy annuals will be sown in the positions where they are to flower and half-hardy kinds planted out from pots or boxes when weather conditions allow.

As with herbaceous border plantings, bold groups of the same plant create the biggest impact, so quantities of the same variety must be grown in order to make a show. Unlike permanent bedding, however, it is not essential that each group of plants should be the same shade. Very fine patchwork effects can be obtained by using mixed coloured eschscholzias — for instance — in one block, variously hued linarias in another — and so on.

Sowing Hardy Annuals Out of Doors Ideal sowing conditions obtain when the soil is moist and the ground has been raked to a fine tilth beforehand. The smaller the seed — and annual seed is often very tiny — the more important this becomes. If soil particles are in contact with one another, the film of moisture surrounding each is readily available to the first, all-important plant roots. Large particles and loose shifting soil make for air pockets and if seedlings fall into these they soon dry up and perish. Tread the ground beforehand therefore if it has been recently dug and then rake it down to a fine, smooth, even tilth.

Unless the plants are intended for cutting purposes avoid sowing annuals in straight lines. A good idea is to mark out individual areas beforehand, making these informal but running into each other like a jigsaw puzzle. Sometimes it is enough to draw lines with a hoe for this purpose or sand can be used to make a bolder outline. If each section is labelled with the name of the intended occupant it is easier to work methodically, sowing as one goes and also reserving spaces for the half-hardy annuals which cannot be planted out until later in the season.

Seed can either be scattered broadcast within the prescribed areas and then lightly raked in, or a pointed stick can be used to trace narrow drills. Sow thinly and later fill in the drills with the head of a rake – held in an upright position so that the teeth cannot dig into the ground and the seeds are only just covered. Water if necessary.

When the plants germinate weed between the rows and then thin the seedlings to 1 in. apart. If they are to develop to full size and maturity a second and more drastic thinning will be necessary. This final spacing will be determined by the type of plant and its spread and ultimate height, but as a rough guide, plants growing 12 in. in height under good conditions should be thinned to about 6 in. apart: those of 18 in. to 9 in. and any 2 ft. or thereabouts left 1 ft. away from neighbours. Most annuals are self-supporting, but weak-stemmed varieties or plants in ,windy positions can be made secure with the aid of twiggy peasticks.

Keep the hoe going to eradicate weed seedlings and loosen the soil until the plants have grown sufficiently to render this unnecessary. Late germinating weeds will then be smothered at birth and any survivors can just be pulled out by hand.

The sowing of hardy annuals takes place out of doors in late spring (April to May in Britain). Typical of plants which can be treated in this manner are Shirley poppies, Virginian and night-scented stocks and nasturtiums.

Autumn Sowing

On well-drained soil and in favoured situations, hardy annuals are frequently sown out of doors the autumn prior to flowering. If all goes well – and it is a calculated risk, for winters are always unpredictable – they make stronger plants and bloom earlier than those raised in spring.

The beginning of September is the best time to sow in Britain; a little earlier in cooler climates and slightly later in warmer areas. The prospects of success are improved if cloches are placed over the seedlings in severe weather.

Although all annuals are not suitable for autumn sowing the following may be tried with reasonable success: calendulas, larkspurs, sweet peas, nigella, eschscholzias, cornflowers, annual scabious, godetias, clarkias and linarias.

Sowing Under Glass

Half-hardy annuals are prone to frost damage, so to give them a good start they are first raised under glass, then potted separately or spaced out in boxes, and finally put outside in their flowering positions when the weather improves. In Britain it is usually safe to do this at the end of May or early in June – a week or two later in northern Europe or the north eastern states of northern America.

Growing temperatures will naturally vary according to the type of plant, but the hardier kinds for outdoor planting will do quite well in a frame or greenhouse from which frost can be excluded. Tender annuals will need temperatures of approximately 15 to 18°C. (60 to 65°F.) later.

In all cases the soil should be light and friable. Equal parts of coarse sand (or perlite), good sifted loam and peat moss or sphagnum moss provide the foundation of most home-mixed composts. Alternatively one can buy packaged composts, which have the advantage of added nutrients. John Innes Seed Compost is commonly used in Britain or General Purpose Soil in the United States.

The containers, whether pans, pots or boxes, must be scrupulously clean and crocked if there is only one drainage hole, with a little peaty material above the crocks to prevent blockage. They should then be filled with damp compost. Firm lightly and leave a smooth finish.

Now sow the seed thinly and cover it with silver sand or finely sieved compost. Label the pots and stand them in a shallow bath of water so that the liquid is just below the rims. Leave them there until the soil surface looks damp. This method does not dislodge the seed as much as top watering with a can.

Remove the containers to a frame or greenhouse and cover them with glass and a sheet of newspaper. The glass must be turned daily to prevent too much condensation and both coverings removed when germination takes place.

When large enough to handle prick out seedlings 2 to 3 in. apart in boxes or pot them separately and grow on.


Biennials are sown outside in shallow drills in spring or early summer (normally between April and June) for flowering the following season. Some, like meconopsis and primula, should be sown directly after harvesting as the seed deteriorates with keeping. The procedure is similar to that of hardy annuals except that the plants are raised in sheltered nursery beds (which can be shaded if necessary) and have a fine sowing tilth. They are then thinned to 6 to 9 in. apart in the rows and lifted and planted in their flowering positions in early autumn or the following spring.

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