Top of the Crops - Sunflower

Welcome to Top of the Crops! Today, you will learn about growing sunflowers in polytunnels in the UK. Produce a heavy seed crop by following this in-depth guide.

How to Grow Sunflowers

Sunflowers can be a cheerful and attractive choice for your garden. But they are more than just an ornamental. Sunflowers are also an edible crop in their own right, and can also be useful as a companion plant and trap crop in a polytunnel garden. 

Key Information

Annual sunflowers, Helianthus annuus, are very easy flowers to grow in a garden. Growing them makes a fun garden project for kids and adults alike. A good choice for a novice gardener, they can also be useful for more experienced home growers, who will find them very useful as edible crops, wildlife attractants, and companion plants. 

There are also a number of hardy perennial sunflowers to choose from, which are also well worthwhile considering for many of the same reasons. But in this guide we will focus on the enduringly popular annual type. 

Annual sunflowers are not only useful in a garden, and beautiful, they can also help teach children about the sunflower lifecycle and other features of the natural world. 

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

The Preferred Conditions for Growing Sunflowers

If you would like to grow sunflowers in your garden then of course one of the first things you will need to decide is where to do so. 

Sunflowers can be grown in a range of different locations and situations. They might be grown:

  • In a garden border. 

  • As a companion plant in vegetable beds.

  • In containers. 

They can be grown outside through summer in UK gardens but can also be sown within a polytunnel where there is sufficient space. You need to remember that some sunflowers will grow much taller than others and dwarf varieties are best for undercover growing, and are also often best for containers. 

As their name suggests, sunflowers like a position in full sun. Especially for taller members of this species, a sheltered position is best. The soil or growing medium should be reasonably fertile, rich in organic matter, and moist yet free draining. 


What You Will Need to Grow Sunflowers

To grow annual sunflowers from seed you will need:

  • Sunflower seeds of your chosen variety.

  • Small pots or other containers if not direct sowing in the ground or raised beds. 

  • Seed starting compost if not direct sowing. 

  • A small spade or trowel for planting out if not direct sowing. 

  • Support (sometimes) for taller varieties. 

How to Grow Sunflowers

Growing sunflowers from seed is not at all challenging, it is something complete beginners of all ages can try. The seeds are large and easy to handle and the plants don't require a great deal of care. 

Sowing Sunflowers

Sunflower seeds are usually best sown indoors into individual small pots or other containers filled with a suitable seed starting potting mix. The usual time to do this is in spring, between March and May.  Sow seeds a cm deep or so. 

You can also sow sunflowers directly where they are to grow once the last frost date has passed and the soil has warmed where you live in late April or May. Again, sow seeds to a depth of around 1cm and aim to place seeds around 10cm apart. These can later be thinned to give the right spacing. 

How to Plant Sunflowers

Whether you have grown your own or purchased plants in pots, sunflowers should be placed into their growing positions in the garden once the weather has warmed reliably where you live. 

Remember to harden off plants grown indoors before you place them into their final growing positions outside to avoid any issues or checks to their growth. 

Aim for a final spacing of around 45cm between plants, though this may be a bit less or a bit more depending on the specific type and variety of sunflower that you have chosen to grow. 

Dig your planting holes, place the plant, then firm the soil or growing medium back into place around the sunflower roots. Insert stakes or canes where these are required for taller sunflowers upon planting. 

Water the new additions in well, and add a mulch of compost or other organic matter around the base of the plants to get them off to a good start. 

Pinching Out Sunflowers

If you are trying to grow sunflowers as tall as possible, then pinching out is not something that you will generally want to do. 

However, if you want more blooms rather than the biggest/ tallest possible then you might wish to pinch out the growing tips of some varieties to encourage more blooms. 

Pinching out simply involves extracting the top of the plant, nipping if off with a finger and thumb. You will typically do this when the plant is around 20-25cm in height. The plants will then produce many smaller heads rather than one big one if they are of a suitable variety for this practice. 

Care Tips for Growing Sunflowers

Caring for annual sunflowers is largely a question of watering and feeding well. These plants like plenty of water and plenty of nutrients to perform at their best. 

Water regularly throughout the growing season to maintain consistently moist conditions. In low water conditions or water shortage, sunflowers will tend to experience checks to their growth and will not grow as tall or flower as well. 

Whether you are growing in the ground or in containers, sunflowers are best fed with an organic, potassium-rich liquid plant feed to promote healthy flowering. 

Harvesting Sunflowers

As the plants begin to die back in the autumn, you can collect the flowering heads which are filled with seed. Note that you will be in competition with the birds and other wildlife for these seeds and so may have to cover the heads as the seeds mature to protect them from all being eaten. 

Of course, it is good to share some of the harvest with the birds and other wildlife that shares your space. So leave a head or two in place for local birdlife to enjoy. Seeds are ready for harvesting when the florets are brown at the centre and the heads rotate down to face the ground. 

One thing to remember is that you will need to remove the tough outer coating from the sunflower seeds before they can be eaten. You can also simply dry out the seeds for a few days and then store them to plant the following spring. 

Cutting Sunflowers for Bouquets

Of course, you may also have harvested sunflowers earlier in the growing season while the flowers were at their peak to use as cut flowers for bouquets or for displays inside your home. These make great cut flowers for many different uses. 

Propagating Sunflowers

Sunflowers are easy to grow from seed, and you should consider saving your own seeds each year so that you can continue to enjoy annual sunflowers in your garden each year. 

Varieties of Sunflowers to Grow

When choosing which sunflower or sunflowers to grow, you need to think about height, whether they produce single large flowers or multiple smaller blooms, flower characteristics, etc... Some highly regarded sunflower varieties to consider include:

  • American Giant

  • Buttercream

  • Claret

  • Dwarf Sungold

  • Munchkin

  • Pastiche

  • Solar Power

  • Sunsation Yellow

  • Teddy Bear

  • Valentine

All of the above have an award of garden merit from the RHS. 

Common Pests and Problems 

Sunflowers are not usually prone to a great many pest or disease problems. However, slugs and snails can be a particular problem when the plants are young – so make sure you protect them during this time.  It can help to make sure that the plants are larger and tougher before you plant them out if slugs and snails are a problem where you live. 

Cooking Sunflower Seeds

Once you have shelled sunflower seeds the kernels can be eaten raw, or they can be roasted before they are eaten. Roasting is a good idea for flavour and because it makes the shelling process easier. 

You can roast the sunflower seeds unshelled and shell each one as you wish to snack. Or use a rolling pin to roll over the seeds to remove the outer casing. If you want the seeds salted then you can if you wish soak them in salt water before you roast them. 

Advice for Buying Sunflowers

Before you decide which sunflower seeds to purchase for your garden, think about what you want to obtain and where you wish for them to grow. 

Remember, there are giant sunflowers that grow in excess of 2.5m in height, others that are tall but not giant, and much smaller dwarf sunflowers to choose from. Some are suited to producing large, single heads while others are best for multiple smaller flowers. Make sure you choose a variety or varieties that are suited to your needs and wishes. 

Top Tips for Growing Sunflowers in a Polytunnel

For polytunnel growing, it is usually a good idea to select dwarf cultivars, which are suited to growing inside a confined space. Dwarf sunflowers can be excellent choices for beds, borders or containers within a polytunnel garden. They make excellent companion plants as attractants or trap crops and will benefit many of the fruits and vegetables grown close by. 

By growing sunflowers in your garden or polytunnel, you should be aware that they might attract certain types of wildlife, including ones that you do not want near them, which may include birds. In which case, its important to know what attracts birds to your garden.


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Sunflower Life Cycle. Twinkl. [online] Available at: [accessed 14/12/23]

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