Annuals, Biennials and Perennials – Hardy and Half-Hardy Plants

Annuals, Biennials and Perennials

Herbaceous plants can be sub-divided into hardy and half-hardy plants. The terms apply to annuals, biennials and perennials alike and means, briefly, seeds that can be sown outside directly into the soil (hardy) and those that need some protection and gentle warmth to enable them to germinate (half-hardy).

The hardy annuals are the simplest of all plants. They are quick-growing, can be sown in the open ground when the soil warms up (in Britain this normally means between March and May), and thinned out if necessary.

The half-hardies are usually started earlier in a heated greenhouse to aid germination and are then hardened off in an unheated but protected area, such as a cold frame, before being planted out. This can be done as seedlings (when only the two seed-leaves have appeared) or as bedding plants. With some you can take a chance, delay a couple of months or so and treat them as hardies, trusting to luck and a good summer that they will come into flower, even if later than the scheduled time.

Unfortunately, if you are dealing with a plant whose seed cannot be sown successfully until, say, May, you cannot expect it to flower before June and by then you are at the height of summer. Many will be in bloom for no more than three weeks, possibly less, but you can prolong the flowering season to some extent by successional sowing, at weekly or fortnightly intervals.


The lack of flowers in spring and early summer is a matter for regret, but there are other means of filling the space effectively. The important factor is that throughout the longest and warmest days of the year your garden can be filled very cheaply and most satisfactorily with annuals and biennials.

And when they do appear, what a wide range they cover! You can use them as edging at the front of a border; you can have them filling beds and borders on their own; you can have them climbing up fences, walls and trellises or hanging gracefully from baskets and window boxes. You can have them reflecting the sun or bringing cool grace to a shady corner. You can alternate between clusters of tiny flowers no bigger than a thumb nail and massive blooms 10cm (4in) in diameter — or more, and you can plan a floral display at any height from 10cm (4in) to 120cm (4ft) or more.

Some have no flowers worth mentioning but score heavily with the magnificence of their leaf colouring. Some have a subtle perfume to add to their beauty of form. There are even a few that offer fragrance from the leaf. As for colour, you can have every shade except jet black, and doubtless it will not be many years before even that is achieved.

One of the many attributes of annuals and biennials is that they ask for little attention. Given freedom from pests something will show from seed sown even in the poorest soil. Naturally, some previous attention in preparing the area will prove beneficial, but this need not be of an elaborate nature. All that is necessary is to dig over the soil beforehand — the previous autumn clean-up time is ideal — work in a little manure or compost and, for long-term benefit, some slow-acting bone meal. Level the ground and rake it to a fine tilth just before sowing, so that there are only tiny particles of soil, in which the seed can lie comfortably without being suspended in an air pocket. Remember that seed must be in contact with the soil, so that the bacteria there can get on with their work of bringing it to life.

With half-hardies, or other plants germinated in a seed tray in the greenhouse for extra starting warmth, the procedure is similar but on a smaller scale. The seed is placed in the fine compost, covered lightly with it, and kept dark until germination so that the sun does not dry out the compost.

Some seed, bought in pelleted form, looks huge, being coated with a clay-like substance. Pelleted seeds are more expensive but carry some benefit as they are easier to handle and involve less wastage, for the thinning-out chore is either greatly reduced or eliminated altogether. They usually take a little longer to germinate because the coating has to be broken down by the moisture in the soil, so it is helpful to depart from the usual rule and give a light watering immediately after sowing. ‘Light’ is the important word, for the clay material absorbs moisture and if there is too much it becomes a sticky mess that could prevent the emergence of the seedling.

There is another, and smaller, category of seeds known as tender annuals, or greenhouse biennials. These need a somewhat higher temperature in their early stages of germination and are mainly for the greenhouse or conservatory. They are usually grown in pots, but some make colourful and valuable contributions to an outside border. Among them are such favourites as calceolaria, cineraria, primulas, begonias, pelargoniums, coleus and impatiens (balsam or busy lizzie), a list sufficiently imposing to underline the fact that although a greenhouse may not be, strictly speaking, part of a garden, it is an essential part of the equipment of any serious gardener. It enables him to produce a far greater range of plants (and also prolong his colour season all the year round) than would otherwise be the case.


27. April 2011 by admin
Categories: Annuals, Biennials and Perennials, Plants | Tags: , , , , , | Comments Off on Annuals, Biennials and Perennials – Hardy and Half-Hardy Plants


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