Once regarded as crucial elements in any garden, hardy annuals have been out of fashion in recent years. But as they undergo a revival Graham Rice starts a two part series by looking at the basic growing techniques.
The definition of a hardy annual is simple enough. It's a plant that goes through its entire life cycle in one season and which can be sown outside in the open garden in spring where it is to flower. In many areas this carries with it the implication that it can happily survive the spring frosts as a seedling.
But it has to be said at the outset that in practice, this definition is a narrow one. In nature, some annuals germinate in late summer or early autumn and overwinter as young plants before surging ahead in spring. Many plants which have become adapted as weeds of cornfields like cornflowers (Centaurea cyanus) fit into this category. They germinate after harvest and flower and seed in summer, shedding at least some of their seed soon enough not to get collected with the crop. The definition can also be extended to plants which are actually perennial in habit but which flower quite happily in their first year when sown outside and also to plants which are frost tender but which flower so quickly from seed that even in colder areas they can besown outside after the last frost and still give a good display.
Many's the gardening book that has recommended hardy annuals be grown in the hottest sun and the poorest, driest possible soil. There is the hint of good reason for this but it needs dramatic adaptations for the garden. In nature many annuals grow in situations where there is only a short time for them to grow and produce seed. This may be because they grow in semi-arid regions where the soil is only moist following brief seasonal rains and the plants must grow quickly to make the most of this temporary moisture before the sun dries the soil. Or a speedy life cycle may be necessary because the plants grow in unstable soil such as screes, windswept areas or soil frequently disturbed by animals.
In these situations, annuals grow quickly and flower with great flamboyancy but often on small plants and for only a short time. The soil is poor in plant foods and dry so there is a pressure for the whole cycle to be over quickly.
In the garden this is not what is required. Gardeners need their plants to flower for long periods and preferably on plants a little more bushy than the single stems so often seen in the wild. So although annuals will grow and flower in poor, dry conditions for a good display in the garden the soil should be rather better.
Sun is necessary for the best display although most hardy annuals will do well enough in a site that is only in the sun for half a day. Heavy soils are the least suitable for hardy annuals though they can be much improved by the addition of organic matter and especially by forking in sharp sand or grit to improve the drainage. Good drainage is one thing that really does help most hardy plants. But this should not be taken to such excess that they are constantly thirsty. Good drainage is important, if the soil is retentive too then growth and flowering will last all the longer. Sandy and gravelly soils will be much improved for annuals, as for many other plants by the addition of garden compost.
Hardy annuals appreciate a little more than starvation rations too. Personally I find that on most soils a handful of a general balanced fertiliser such as Growmore (7-7-7) raked in before sowing is quite enough as long as there is some organic matter in the soil. Some recommend an application of superphosphate at sowing time and a general fertiliser later but I have not found this necessary.
The sowing technique for hardy annuals is simple enough, although there are some variations which depend on personal preference.
The site should be forked over lightly, trodden again and then the fertiliser dressing raked in. At this stage opinions diverge but seem to be coming down in favour of sowing in rows rather than broadcasting the seed. So, first check the seed packet for advice on sowing depth and spacing. If your seed comes from a seed exchange, a society or a friend then use your wisdom and your reference books to help.As a guide sow seeds at about twice or three times their own depth - take no notice of the precise recommendations sometimes given in terms of fractions of an inch, we all know that such precision is impossible. Space the rows out at a spacing of about half the eventual height of the plants.
Rake the soil to a fine tilth and then using the corner of the rake, the point of a cane or even a finger well hardened by horticultural toil make a shallow drill of the depth required. If you're sowing a number of hardy annuals in a large group, orientate the rows of the different varieties at contrasting angles to each other rather than parallel to avoid too much regimentallity.
When it comes to the actual sowing of the seed, there are many ways of going about it. I feel that the important thing is to be able to see the seed falling on to the soil so that it can be sown thinly enough, but not too thinly.
Perhaps the easiest way of doing this is to cut the top off the packet with a pair of scissors to leave a clean edge. A crease is then made half way along one side of the cut top and the edges of the packet held between the thumb and second finger. The packet can then be tipped slightly so that the seed runs into the crease and the packet tapped gently with the first finger to dislodge the seed. We are always enjoined to sow thinly and this is very wise. But a balance must be struck depending on the number of seeds available, the viability of the seed and the quality of the soil tilth. Some packets, especially those of newer varieties may not contain many seeds. In that case if the soil is good the seed of many plants can be sown very thinly, say at 1 inch (2.5cm) intervals, but if the soil is less good, sowing at a closer spacing in just one row may be preferable. Later, seedlings can be transplanted at their final spacings into the other rows. Seed from seed exchanges and from your own garden may not be of the very high germination quality that usually comes from the seed companies so sowing more thickly may be advisable. If it is not possible to work the soil into a fine tilth this too may necessitate sowing less thinly.
Covering the seed is a simple matter, the back of the rake can be used to draw a little soil over the drills and this can then be tamped down gently by the flat of the rake. If you have a problem with sparrows or other birds taking dust baths in the soil after sowing, stretch some black cotton thread over the sown area or place some twiggy brushwood over the bed to keep the birds off.
The speed at which the seedlings come through depends on the weather. If the tilth was well prepared and you have used seed from a seed company you will probably find germination is fairly even. Otherwise it may be a little erratic. The seed packet will usually give you a recommended final spacing and at the first thinning you should not remove all the seedlings that will eventually be unwanted. First of all thin to give an inch (2.5cm) between seedlings, then to half the eventual spacing as the seedlings grow then eventually to the final spacing. That way, if anything goes wrong there will always be a few spares.
Thinning without disturbing the seedlings you wish to retain can be difficult. The first thinning when the seedlings are small can usually be done simply by pulling the seedlings sideways away from the row, they should come out quite easily. If the soil is dry, water the drills well before starting. At the next thinning use the following technique. Place the first and second fingers closely on either side of the seedling you wish to retain and press firmly on the soil. This will keep the seedling in place while you remove other unwanted seedlings with the other hand. If you wish to transplant seedlings, use a narrow trowel such as a bulb trowel to remove seedlings individually with a little soil on their roots. Plant them at once and water them in promptly.
Many hardy annuals need support, especially in garden soil which is a little bit richer than the soil they find in their wild homes. This encourages them to grow a little taller and a little softer than they would normally - as well as flowering better. There are a number of different ways of supporting the plants.
The simplest is probably to use brushwood to support the plants that experience tells you are likely to flop. In different areas different materials are available but hazel (Corylus avellana) is especially good as it grows in flat, fan like sprays making ideal supporting material. But although hazel is the best natural support, birch or whatever other twiggy material is available is good too. Choose twigs which when pushed firmly into the ground reach a height of about two-thirds of the eventual height of the plants concerned. Place it around the group when the plants are still quite small so that the plants never flop and secure it by running string all the way round looping it around the main branches as you go. A few extra pieces in the middle of larger groups can be useful. As the plants get larger side branches will grow through the twigs and hide them.
An alternative that is easy for anyone to get is bamboo canes and although less attractive they are nevertheless very serviceable. Put a cane in at each corner of the group and run strings around and across. Use strings at two heights for taller plants.
Another method which I've found to work well for beds and borders given over entirely to hardy annuals is to use netting. Immediately after sowing all the groups knock in stakes at the corners of the bed and at 2ft (60cm) intervals in between. Then cover the bed in wide mesh plastic netting, the sort used to support peas and beans is ideal. Slide it over the posts and lay it on the ground where it will prevent birds creating havoc.
When the plants come through lift the netting slightly and in stages to a height of about 9 inches (23cm) so that the plants can grow through.
The same idea can be adapted for individual groups by using dahlia stakes and smaller pieces of netting or sometimes two pieces at different heights for taller plants.
In Hardy Annuals Part 2 I shall discuss late summer and autumn sowing, watering and other cultural matters and I shall recommend some unusual varieties.
Graham Rice is author of A Handbook of Annuals and Bedding Plants published by Christopher Helm (UK) and Timber Press (USA).
Source of article
Growing From Seed - Spring 1988 Vol. 2 Number 2
© The Seed Raising Journal from Thompson & Morgan