How to Grow Cornflowers: A Practical Guide from Seed to Flowers

Cornflowers are an easy annual flowers to grow from seed and a good choice if you're fairly new to growing flowers. They don't need complicated treatment, grow quickly once the weather improves and can give you masses of flowers through summer.

The traditional blue cornflower is probably the one most of us recognise, but garden varieties are available in different colours and flower forms. Double varieties such as Crown Double Blue give you fuller flowers while keeping that lovely rich cornflower blue.

I like cornflowers because they're equally at home in an informal border or a patch grown specifically for cutting. The flowers are excellent in a vase, and the more you pick and deadhead them, the more reason the plants have to keep producing flowers.

They prefer a sunny position and don't need particularly rich soil. Sow them directly outside if you want to keep things simple, or start a few under cover for an earlier display.

When to Sow

Cornflowers can be sown in spring or autumn.

For spring flowers, sow from March to May. You can start seeds under cover, but they're so straightforward to direct sow that I generally don't think there's much need to create extra work.

Sow outside once the soil is workable and beginning to warm.

You can also sow from August to October. Autumn-sown plants establish before winter and usually flower earlier the following year.

I like doing a little of both if I have enough seed. An autumn sowing gives you an earlier start, while another sowing in spring can help keep the display going later.

Don't worry if autumn-sown plants remain fairly small over winter. They'll start moving again once conditions improve.

How to Sow

Cornflower seeds are large enough to handle without too much difficulty.

For direct sowing, prepare the ground by removing weeds and raking the soil to create a reasonably fine surface.

Make shallow drills around 1cm deep and sow the seeds thinly.

Cover with soil, gently firm the surface and water if conditions are dry.

If you're sowing several rows for cutting, leave around 30cm between rows so you can get between the plants later.

You can also start cornflowers in pots or modules. Sow a couple of seeds per module, cover lightly and keep the compost moist while they germinate.

Once seedlings appear, give them plenty of light.

Cornflowers don't need lots of heat. They're hardy annuals, so they're considerably more tolerant of cool conditions than tender flowers such as petunias or marigolds.

Thinning and Growing On

Once direct-sown seedlings are large enough to handle, thin them if they're badly overcrowded.

Aim for roughly 15–25cm between plants.

If you're growing for cut flowers, a little extra space encourages plants to branch and produce plenty of flowering stems.

Don't worry about achieving perfect measurements. You're simply trying to stop every plant competing with six neighbours for the same patch of soil.

Keep weeds under control while the seedlings are small.

Once established, cornflowers grow quickly and don't need much attention.

If you started them in modules, plant them outside while they're still reasonably young. Water them after planting and keep an eye on them until the roots settle.

Growing Cornflowers in Pots

Cornflowers can also be grown in containers.

Choose a reasonably deep pot with drainage holes and place it somewhere sunny. I'd use a larger container with several plants rather than trying to make one cornflower fill an entire pot.

Fill with multipurpose compost and either sow directly or plant young seedlings into the container.

Don't overcrowd them. Cornflowers can become fairly substantial plants once they're flowering.

Container-grown plants need more regular watering because the compost dries faster than garden soil.

Taller varieties may also need a little support, particularly if the pot is somewhere exposed.

If you're specifically looking for very compact container flowers there are better choices, but there's no reason you can't enjoy cornflowers in a decent-sized pot if that's the space you have.

Watering and Feeding

Cornflowers are fairly undemanding once established.

Keep seedlings and newly planted flowers watered while their roots develop. After that, plants growing in the ground usually only need extra water during prolonged dry weather.

Containers need checking more frequently.

There's generally no need to feed cornflowers heavily.

In reasonable garden soil, I'd normally leave them alone. Very rich conditions can encourage lots of soft leafy growth and taller plants that are more inclined to flop over.

Container plants that have been growing for a long time may appreciate an occasional feed, but don't assume that more fertiliser automatically means more flowers.

Give them sunshine, reasonable soil and enough water. That's usually plenty.

Flowering and Deadheading

Cornflowers usually begin flowering in early summer and can continue well into late summer if they're regularly picked or deadheaded.

This is where a little attention really pays off.

Once a flower starts fading, remove it before the plant puts lots of energy into producing seed. That encourages more flowering shoots to develop.

You don't have to inspect the plants every morning. I generally go over them every so often and remove the flowers that are obviously past their best.

If you'd like to save seed, leave a few flower heads towards the end of the season to mature.

The plants may eventually become a little tired and untidy. That's normal for an annual 

Growing Cornflowers for Cutting

Cornflowers make excellent cut flowers and are one of the reasons I'd grow a few extra plants.

For the longest vase life, pick flowers when they're fresh and newly opened rather than waiting until they've been fully open in the garden for several days.

Cut the stems in the morning if you can and put them into water fairly quickly.

Regular cutting has another advantage — it encourages the plants to keep flowering.

If you're growing specifically for the vase, plant several cornflowers together so you can take a handful of stems without leaving the garden looking bare.

Double-flowered varieties such as Crown Double Blue are particularly attractive for cutting because the fuller blooms make a lovely display.

And don't worry about cutting them. A productive cornflower plant usually responds by producing more.

Pinching and Supporting

You don't necessarily need to pinch cornflowers, but removing the growing tip from young plants can encourage them to branch and produce more flowering stems.

If you decide to pinch, wait until the plant is established and has several sets of leaves, then remove the top growing tip.

It's optional rather than essential.

Taller cornflowers can sometimes lean or flop, particularly in rich soil or exposed gardens.

Plants grown together often support one another perfectly well. If necessary, use some discreet canes, twine or plant supports before the stems start falling over.

It's much easier to support them while they're still upright than to attempt a rescue operation after a night of wind and rain.

Saving Seed

If you'd like to collect seed, stop deadheading a few flowers towards the end of summer.

Allow the flower heads to mature and dry on the plant.

Once they're properly dry, collect the seed and store it somewhere cool and dry until you're ready to sow again.

Cornflowers can also self-seed if mature seed is allowed to fall onto suitable ground.

You may find a few seedlings appearing the following year, although I wouldn't rely entirely on self-seeding if you want a particular variety in a particular place.

With named varieties, saved seed may not always give plants exactly identical to the original, particularly if other cornflowers have been flowering nearby.

Common Problems

Slugs and Snails

Young cornflower seedlings can be damaged by slugs and snails, particularly during damp spring weather.

Keep an eye on them while they're small. Once the plants are established, a little leaf damage generally doesn't cause much trouble.

Aphids

Aphids can occasionally gather around tender shoots and flower buds.

Small colonies can often be washed away or left for beneficial insects to deal with. Check plants occasionally rather than waiting until an entire stem is covered.

Plants Becoming Tall and Floppy

This is often worse in rich soil or where plants are crowded and reaching for light.

Give them plenty of sunshine, don't feed excessively and provide some support if your garden is exposed.

Few Flowers

Too much shade can reduce flowering.

Cornflowers perform best with plenty of sunshine. Excessive feeding can also give you lots of green growth without necessarily improving the flower display.

Flowers Finishing Too Quickly

If plants are allowed to produce lots of mature seed, flowering will naturally begin to slow.

Regular cutting and deadheading encourages them to keep producing new flowers for longer.

Powdery Mildew

A powdery coating can sometimes appear on the foliage later in the season, particularly when plants are stressed or airflow is poor.

Give plants reasonable spacing and keep them watered during prolonged dry weather. If an otherwise healthy annual develops a little mildew towards the end of summer, I wouldn't worry too much about it.

Cornflowers are exactly the sort of flower I'd recommend when someone wants plenty of colour without complicated growing. Sow them outside in spring, give them sunshine and start cutting or deadheading once the flowers appear. Crown Double Blue is a lovely example — that familiar cornflower blue, but with fuller flowers that look just as good in a vase as they do in the garden.