6 Common Reasons Why Your Garden Plants Aren’t Flowering (and how to fix it!) – The Middle-Sized Garden

6 Common Reasons Why Your Garden Plants Aren’t Flowering (and how to fix it!) – The Middle-Sized Garden

July 22nd, 2023
Posted In: Gardening know how

Are you looking at plants in your garden and wondering why they aren’t flowering?

I am. And I’ve discovered a surprising reason why my cosmos plants don’t even have any buds on them.

So to get to the bottom of what stops garden plants from flowering, I asked local flower farmer, Sue Oriel of Country Lane Flowers, to explain it and suggest effective solutions.

Sue and her business partner, Stephanie, grow all the flowers for Country Lane Flowers in their own gardens. They create locally sourced, sustainable flower arrangements for weddings and supply bouquets, so if there’s one thing they can’t afford it’s flowers not flowering!

6 reasons why your plants aren’t flowering

  1. You’ve planted it in the wrong place in your garden
  2. The age of the plant (perennials only)
  3. Sowing your seeds too late (annuals only)
  4. Not dead-heading enough
  5. Pruning at the wrong time
  6. Not fertilising enough or using too much fertiliser

Find out why your garden plants aren't flowering

The No 1 reason why your plants aren’t flowering

You’ve planted it in the wrong position. ‘If you plant sun-loving plants in too shady a spot, then they’ll get leggy with few or no flowers,’ says Sue.

Shade-loving plants, such as foxgloves and hydrangeas, will flower in the shade.

But sun-lovers, such as lavender, cosmos, dahlias, zinnias, sunflowers and more, need full sun.

Iris experts Irises of Sissinghurst say that the number one reason for irises not flowering is that their rhizomes are buried too deep. Not only does the iris plant itself need full sun, but it needs sunshine on the top of rhizome.

‘Full sun’ in the gardening world is defined as ‘six hours or more of direct sunshine a day in summer’.

How to fix it: move the plant to a position where it will get the right amount of sun. It’s better to move plants in spring or autumn. Summer can be too hot and dry, but winter can be too cold and wet.

Dahlias won't flower in a shady spot - they need full sun.

If a plant needs full sun, such as a dahlia, then it will flower very little or not at all in deep shade. This is Dahlia ‘Wizard of Oz’

The age of the plant (perennials only)

Perennials are plants that live in your garden for three years or more. To find out more about them, see perennials made simple.

I am re-vamping my border, so I have planted lots of 9cm perennials, such as geums and hardy geraniums.

They have flowered but they’re not huge clumps of flowers. But that’s not surprising. It will take many perennials more than one summer to get big enough to flower profusely.

And at the other end of the spectrum, many perennials spread in the border. After three or four years, the original part of the plant will die off in the centre leaving a ‘bald patch’ with no flowers.

Sue says that the way to deal with this is to dig up and divide clumps of perennials if you can see that the centre of the clump isn’t flowering. This is best done in spring and autumn.

How to fix it: As Sue says, you may have to hack a particularly stubborn clump of perennials to pieces once you’ve dug it up. But you’ll be able to throw away the old dead roots and re-plant several sections of new root.

‘But sometimes plants just die. That’s normal,’ says Sue. A professional gardener once told her that you should plan on replacing about 10% of the plants in your border every year.

The geums in my border were only planted a few months ago. They haven't reached their full flowering peak yet.

The geums in my border were only planted a few months ago. They haven’t reached their full flowering peak yet – I hope!

Sowing seeds too late (annuals only)

Annuals are plants that are grown from seed, flower, then set seed and die, all within 12 months.

‘Annuals need 14-21 days to germinate, then 90-100 days of growth before they flower,’ says Sue. ‘It’s simple maths. If you sow the seed too late, you don’t have enough time to reach flowering before the temperatures drop and the daylight shortens.’

How to fix it: She says that the answer is to sow seeds of hardy annuals in autumn. Then keep them somewhere cool but frost-free (like a greenhouse or a windowsill) over the winter.

Not all seeds can be planted in autumn to flower the following summer. So if you’re planting seeds the same year you want them to flower, Sue suggests leaving it no later than mid-spring (March for the northern hemisphere).

Not dead-heading your flowers enough

Sometimes you’ll see ‘deadhead flowers weekly’ in the gardening ‘to do’ lists.

Dead head flowers to keep them flowering

Sue dead-heads flowers as soon as they begin to look even slightly scruffy, like one of these Cosmos ‘Apricotta’. She can’t put even slightly tatty flowers into a bouquet or wedding decorations!

Dead-heading encourages more flowering. If your plants are repeat-flowering, then dead-heading them frequently will stimulate them to pump out more flowers.

But what is ‘frequently’? When I interviewed Frances Moskovits about her amazing herbaceous border, she told me she dead-heads about four times a day.  By that, she means that she keeps snips by the back door and in the shed. When she goes out into the garden, she takes the snips and dead-heads any flowers she can see that are going over.

She recommended Darlac snips to me. I bought a couple of pairs and dead-head much more regularly than I used to. (Note that links to Amazon are affiliate, see disclosure)

How to fix it: Sue says she dead-heads around three times a week. ‘But when flower farmers are harvesting their flowers, we’re also effectively dead-heading before the flower head has died! That’s why we get so many flowers – we’re always cutting them!’

The RHS has also recently recommended that you should dead-head flowers as soon as they start to look scrappy rather than waiting for them to die completely.

She says that flower farmers also dead-head down to a leaf node. ‘We don’t leave a stalk. And that encourages repeat flowering too.’ There’s more about dead-heading here.

Not all plants are repeat flowering. But repeat-flowerers include dahlias, cosmos, many roses, astrantias, penstemons, hardy geraniums and more.

You’ll also probably want to leave some plants to go to seed. Seed heads look beautiful in winter and provide food for the birds. And if you harvest your own seeds, you’ll need seedheads too.

Regular dead-heading and cutting the whole stalk off are the key to repeat flowering.

Regular dead-heading and cutting the whole stalk off are the key to repeat flowering.

Pruning at the wrong time

I’ve interviewed specialist plant experts on growing specific plants, including hydrangeas, roses, salvias and irises.

I always ask the expert ‘why is my (insert plant name) not flowering?’

Neil Miller, head gardener at Hever Castle, where they have a famous rose garden, says that the most common reason for roses not flowering is that they’ve been pruned too late.

Roses flower on stems that grow in the same year. So if you prune a rose later than early spring, you’re probably cutting off this year’s flowering growth.

And Roger Butler of Signature Hydrangeas says that the main cause of hydrangeas not flowering is that they’ve been pruned wrong. Different types of hydrangea need different types of pruning. There’s a really easy guide to pruning hydrangeas here.

How to fix it: Find out when your plants need pruning – don’t just hack away when you have the time.

Not fertilising enough OR using too much fertiliser

My interview with Neil Miller completely changed how I grow roses. He explained that roses need more feeding and fertiliser than most plants.

I now use a rose fertiliser and it has transformed my roses. They have more than double the flowers they had before.

But too much fertiliser can cause other plants to become green and leafy, without flowers.

We had a big bag of fertiliser which someone gave me. Our puppy discovered it and tried to eat it, so I thought it would be a good idea to generally scatter it on borders to get rid of it. I don’t normally use fertiliser except for specific plants. (See here for how to puppy proof your garden)

My cosmos plants have grown green and luscious with the extra fertiliser – but many don’t have flower buds on them. Sue says that some plants – such as cosmos and pelargoniums – won’t flower if their life is too easy.

I thought back to last summer when I packed a big pot full of pelargoniums and took very tender care of it. I watered it and fed it. It had about two flowers. In the past, I’ve neglected pelargoniums and they’ve flowered just fine.

How to fix it: Veg, roses and pots need extra fertiliser but many other plants don’t. So don’t just add fertiliser in the hope that it will improve flowering.

Check whether a plant needs extra fertiliser - if you keep your soil in good condition, many don't.

Check whether a plant needs extra fertiliser – if you keep your soil in good condition, many don’t.

See the video on why your garden plants aren’t flowering

See the interview with Sue and some more views of her garden in this video.

Video on why your flower border isn't flowering

Pin to remember common reasons why plants stop flowering

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6 common reasons why your garden plants aren't flowering


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