Gladioli are instantly recognised by their spires of blooms and vibrant colours and are a favourite in the garden and as cut flowers. A single flower spike can produce up to 20 buds, so gladiolus not flowering is a big disappointment – especially as their leaves aren’t particularly interesting in their own right.
There are lots of reasons for gladiolus not flowering, including the age of the corms, the planting technique and care regime, with some issues easier to remedy than others. To help you get to the bottom of why your gladiolus aren’t flowering, we asked the experts for their advice and solutions to ensure beautiful blooms every year.
1. The age of the corms
If your gladiolus has flowered reliably for years and has suddenly stopped, it could be due to the age of the corms. Corms are similar to bulbs and will multiply as the plant grows, creating new plants.
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‘Corms that have matured and flowered for a few years will produce new corms that will eventually replace the parent plant. As well as a new main corm, the plant can also produce smaller cormlets that emerge from the seam between the old and new sections,’ explains Richard Barker, horticultural expert and commercial director of LBS Horticulture.
‘First year corms are smaller than the parent corm and often will not bloom, only producing flowers in their second year of growth. Cormlets may take up to three years to bloom. If you divide an existing clump, only replant the largest corms, as these will produce the most buds. First-year corms and cormlets can be planted in pots and then placed out of the way to mature for a year before being planted out.’
If you want guaranteed flowers and your corms are a few years old, it might be investing in a new set. Crocus have a wide range of gladiolus corms available each winter – the mixed colour collection would be perfect for beginners.
2. Not enough sun
Gladiolus need full sun to bloom: ‘at least six hours of direct sun each day to produce strong flower spikes,’ says Morris Hankinson, managing director of Hopes Grove Nurseries ‘If they are planted in too much shade, they produce more leafy growth instead of flowers.’
If you have planted your gladiolus bulbs in pots, then you can easily move your pot into a sunnier spot. Of course, this needs to be done early in the growing season to ensure there’s enough time for flower stems to develop and bloom.
For gladiolus planted in the ground it is, unfortunately, a case of waiting for the leaves to go over in autumn, digging up the corms and replanting in a sunny spot next spring – February is a great time to plant gladiolus.
3. Feeding with a nitrogen-rich fertiliser
If your corms are not too old and are planted in a sunny position, still your gladiolus is not flowering it may be worth double checking your fertiliser.
Nitrogen rich feeds – which includes many general fertilisers – encourage leafy growth at the expensive of flowers. ‘Instead, switch to a potash-rich feed like tomato food to support flower growth,’ says Julian Palphramand, head of plants at British Garden Centres.
Tomatorite, available on Amazon – is a great option for promoting blooms – or you could try making your own tomato fertiliser. Feed every week or two during the growing season.
4. Pruning the foliage after flowering
One of the biggest mistakes people make when growing gladiolus is pruning the foliage too soon after flowering. This is a leading cause of gladiolus not flowering.
‘To make sure they flower next year, leave the leaves on after flowering and let the foliage stay until it naturally turns yellow. The leaves will photosynthesise and replenish the corm,’ says Chris Bonnett, founder of GardeningExpress. The energy it stores now is essential for growth and healthy blooms next year.
The same rules apply when growing other bulbs after flowering, such as tulips.
5. Planting corms too late
‘You should only plant gladiolus corms when the risk of frost has passed and the soil has warmed up. It can take a few months for gladiolus to bloom, so if they are planted too late or you experience a short summer, the window for buds to develop can be over quickly,’ says Richard Barker, horticultural expert and commercial director of LBS Horticulture.
‘To ensure a good display, you can try starting plants indoors a few weeks before frosts end, and then transplant them outside once the soil is warm enough.’
If planting outside, February is a great time to plant your gladiolus corms.
6. Not planting corms deeply enough
As is the case with many bulbs, getting the correct planting depth can make or break your chance of flowers. In fact, its one of the most common bulb-planting mistakes.
If your gladiolus aren’t flowering, it could be that they have been planted too shallow. ‘If the corms aren’t planted deep enough, the plants become unstable and put less energy into flowering. Corms should be planted about 10 to 15cm deep,’ says Morris Hankinson. This is a similar depth to daffodil bulbs.
To make things easier, you can use a bulb planting tool like this Gardena Bulb Planter from Amazon which has measurements on the side to help you get the right depth.
7 . Keeping the corms in the ground over winter
‘Gladiolus can be left in the ground over winter but will often perform better if lifted and stored as the corms may not grow after a cold, wet winter,’ says Morris Hankinson, Managing Director of Hopes Grove Nurseries.
Lift the corms using a fork, then shake off any excess soil and store in mesh, paper or hessian bags – like these from Amazon – and keep in a cool, frost-free location. You can then replant in early spring.
Lifting gladiolus also gives you the opportunity to manage overcrowding – another leading cause of gladiolus not flowering. ‘Corms naturally produce offsets, and over time these clumps of corms become congested, which can reduce flowering. The congestion causes plants to compete for space and nutrients, impacting flowering. Regularly replacing older corms with the largest newer ones will help maintain strong flowering each year.’
If you want to keep your corms in the ground, covering the top with mulch – like Strulch from Amazon – can help keep the corms viable, though it is no guarantee.
Nothing is more disappointing than a plant failing to bloom, if it’s happened to you this year don’t give up on your gladiolus. Follow our advice to help your current plants or make sure you put these tips into action next year.
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