Our Guide to Growing Annual Plants

Our Guide to Growing Annual Plants

If you are planning a colourful garden this summer but you have never grown annuals before, it’s a lot easier than you might think. If you have a greenhouse for growing annual plants, that’s great, but you don’t need one, particularly if you are prepared to grow later by sowing seed straight into the ground, or you can invest in a few cellular trays if you have a cool but bright window sill or conservatory.

What are annual plants?

Annuals are plants that complete their entire life cycle in one season. Typically they are sown from seed in early spring, grown on and then planted out once the risk of frosts have passed (late May to early June, depending on which part of the UK you live in). They flower through the summer and into early autumn and then generally die once they get their first winter frost. Annuals are distinguished from two other main forms of garden plants:

  • Perennials: these are plants that start growing in spring, flower sometime over summer and put on significant leaf and stem growth, and then die back in autumn/early winter. Unless the winder is exceptionally severe, they then reappear the next spring and go through their whole growing cycle again. Examples of common perennials include peonies, blue geraniums, goldenrod and most deciduous and evergreen trees and shrubs.
  • Biennials: gardeners sow the seeds of biennial plants during one year and then the plants live over winter and then grow to maturity the following year, producing foliage and flowers. At the end of that season, they then die. Biennials that you might have seen include the herb, parsley, sweet William, wallflowers, forget-me-nots and hollyhocks.

Growing annuals from seed

If you choose hardy annuals that you can sow in the ground during April and May, this is the easiest way to produce a summer display of flowers and probably the cheapest. You need to look at the relative heights, spread and colours and incorporate some design if you want a formal flower bed, but scattering some wild flower seeds mixed with various hardy annuals can work very well.

You can also start seeds off earlier by growing them in a greenhouse or on a windowsill. If you invest in a few cellular plant trays these will allow you to grow your own plug plants, ready for planting out later on.

It’s a bit more work as you need to keep the plants watered without overwatering, thinning out as necessary, and make sure the plants get enough light but don’t get so warm that they get too big too fast. Many garden centres now sell trays that are long and thin that have 32-40 individual modules that will fit very neatly on a windowsill.

Ordering plug plants by mail order

This is more expensive than growing your own but it takes away a lot of the uncertainty and is good if you don’t have much gardening experience. When the plug plants arrive in the post, they need to be unpacked from the cardboard as soon as possible, placed upright and given some water. Try to repot them into cellular potting trays or mini pots that same day.

Each one can be removed from its plastic holder using a dibber – a tool that looks a bit like a miniature chopstick. In fact, you can use one of those disposable chopsticks that you can get from Chinese takeaways as they are perfect dibbers.

Poke the fat end of the dibber into the hole at the base of the plant to loosen it and then pull the plant out gently holding its leaves not its stems. Each plant can then be lowered gently into its compost, which is then firmed around the roots using the more pointed end of the dibber.

Buying ready-to-plant plugs

This is the most expensive way to grow annuals, because all of the work has been done for you. However, if you have a small garden, or just a balcony and patio it can be cost effective as you only need a few plants and probably don’t have the space to grow plants from seed. Ready-to-plant plugs are much larger and are available by mail order or from the garden centre during May.

You need to plant them into your pots or into your garden beds after giving them plenty of water, then look after them carefully for the first 3-4 weeks. That means regular watering but also keeping an eye on the weather forecast. If there is a late frost, or the night temperature is set to drop below 5°C, either bring the pots inside, or cover the plants with some fleece to protect them.

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