The Complete Guide to Growing Annual Flowers

It used to be the case that if you wanted to grow flowers year-round, you were limited to inpatiens, marigolds and geraniums. However, greenhouses give gardeners more choices and opportunities to grow a much wider variety of annual flowers. Whether you’re starting a windowbox or just making your garden more inviting, in this guide we’ll help you make the most of the seasons.

One of the things gardeners find most appealing about annual plants is their diversity and variety. Annuals allow creative growers to put together eye-popping combinations of colours that will last a whole season. From bright eye-catching flowers such as Mexican sunflowers and zinnias to the pastel hues of lavatera, annual plants give you a great palette to choose from!

However, the diversity of annuals isn’t limited to colour alone. They come in all sizes, including climbers and grow in many different conditions, from shade loving mignonettes to sun-loving nicotianas. Certain annual flowers are also renowned for their fragrances, such as Heliotropium Aborescens and Matthiola Incana.

An “annual plant” is defined as a plant that finishes one growing cycle over the course of a single season. However, many flowers do not meet this strict definition but are still treated as annual growing plants. Certain flowers such as heliotropes and tuberous begonias are tender perennials that are very fragile and susceptible to the cold, struggling to survive even mild winter temperatures.

However, pansies and other such plants are very resilient to colder temperatures and can survive the worst of a British winter.

Can Perennial Plants Be Annuals?

Tender perennial flowers are defined as plants that will not survive the winter unassisted. Some gardeners essentially treat these plants as annuals, allowing them to die off in the autumn after a growing season, however, greenhouse gardeners can move tender perennials into a milder greenhouse over the winter, meaning that roots and bulbs will be ready for replanting the following year. More common perennials that are treated as annuals include sages such as S. Patens, Verbenas and scented geraniums.

Annuals that respond particularly well to greenhouses are species that are native perennials, by which we mean plants that are native to the country you’re in and accustomed to seasons.

For British growers, Fuschias grow quickly when in a protected, stable greenhouse and can reach heights in excess of 10 feet tall, all while maintaining their multi-coloured blossoms.

Angel’s Trumpet, otherwise known as Brugmansia, can also continue to grow when cultivated in a greenhouse and will flower throughout the year with its fragrant, trumpet-shaped blossoms.

Other perennials that will survive the winter in greenhouses include dahlias, gladioluses and cannas, however, many gardeners opt for digging up these plants bulbs and storing them for replanting the next year instead of trying to maintain year-round growth.

Growing Annuals from Seed

Growing annual flowers from seed can be far cheaper than buying potted plants in the spring. A packet of seeds can cost as little as £2, which would, in turn, grow well over £80 worth of flowers. While more challenging and time and effort intensive growing plants from seed can be far more rewarding than buying infant plants. As well as this, you can be sure that the plants you grow will be healthy and pest-free, something you cannot guarantee from all nurseries.

Additionally, by growing from seed you can grow a far larger range of plants, as even the most well-stocked garden centres won’t carry all the plants you may want. Although most will sell the most popular annual flowers, more niche tastes won’t always be catered for.

There’s good reason for this too, as many annual plants won’t grow well in compact nursery 6 packs and require more soil and root volume to take hold. Therefore, while these plants will happily grow in your greenhouse or garden when planted directly into the soil, a nursery would have a hard time finding the requisite space to grow it.

Therefore, if you want to experiment outside of the most basic of annual plants, you will need to start growing from seed. Many annuals will also self-sow with very little prompting, meaning that you will have a yearly supply of seeds to continue growing your annuals.

Propagating Annuals from Cuttings

Growing from cuttings is an even more efficient way to grow an annual flower. One advantage of propagating with cuttings over seeds is that if you have a specific plant that grows exceptionally well, or is particularly beautiful, you can essentially “clone” it through cuttings.

Once you’ve found a plant you want to take cuttings from, you can essentially keep the plant's genetics going indefinitely. However, propagating from cuttings does come with its own share of challenges and it can be hard to get a cutting to take root.

Late summer is the best period to take cuttings from any plants you want to clone, as it is the end of the growing season. By following these steps, you’ll increase your chances of successfully propagating your annuals:

1. The stem cutting you use is incredibly important. Younger side shoots tend to be the best as they are full of growth hormones. Select a shoot around 2 to 4 inches long and strip the bottom of any leaves so that it can be easily inserted into the potting soil or water.
2. Generously dip the end of the stem into a plant growth hormone. While not essential, these rooting hormones encourage root growth and also reduce the risk of stem rot as the root takes hold.
3. Strip the stem of any buds or flowers. You’ll want the stem to concentrate all of its energy into growing roots, so expending it on growing flowers is not ideal.
4. Liberally water the rooting medium and cover the pot with a transparent plastic bag. Cut some small slits into the top and bottom of the bag to ensure a good circulation of air. Conditions around the cutting need to keep moist and humid.
5. Do not touch or test the cuttings for at least 2 weeks. Burgeoning roots will be extremely delicate, so moving the stem around can break the roots and ultimately kill the cutting.
6. Once the cutting is stable and established, place the plant in a location with a good amount of sunlight and tend to it as you would any other plant.