Gladiolus is one of my personal favorite summer highlights, with its alluring yellow flowers and intense fragrance. But what if you’re disappointed your gladiolus is not flowering this year? Don’t worry! I’ve helped countless customers diagnose various plant problems and find solutions!
In my experience, the most common reason gladiolus does not bloom is planting the bulbs (also known as corms) too late, too close together, or too close to the surface! However, I should warn you that other common reasons gladiolus do not flower are shade, damp soil, and too much fertilizer.
We need to keep in mind that gladiolus typically takes around 2-3 months from planting the bulbs (known as corms) to displaying flowers. I must warn you that flowering is often weather dependent with heavy rain and overcast days during Summer resulting in far fewer flowers.
In this post, I’ll share all my tips to help you diagnose the reason your gladiolus is not blooming, troubleshoot all the common problems, and teach you how to fix it so that it flowers as well as it can…
Keep reading to establish the cause of why you gladiolus and how to promote gladiolus flowering…
But first, I would just like to establish with you that whilst gladiolus are often described as growing from bulbs, they technically grow from corms, which are botanically different but function in a very similar way in a practical sense for us gardeners!
1. Why Your Gladiolus Needs Full Sun To Flower
So, you need to consider whether your gladiolus corms are in enough light. Are they in 6 hours of direct sunlight? From my research, all gladiolus varieties require a location of full sun with 6 hours or more of direct light.
So, for us to get the best blooms from our gladiolus, I always find it is best to understand how and where gladiolus grow in their native environment…
Gladiolus grow in open meadows in South Africa and Mediterranean countries in Europe, where they enjoy full sun and flower gloriously.
I can assure you that you do not need to live in a Mediterranean climate (wouldn’t that be nice?!) it is important to plant your gladiolus in the sunniest area of your garden so that the gladiolus has enough energy to flower.
I have always found that the amount and intensity of sunlight are directly correlated with the display of flowers in the summer.
Whenever anyone tells me that their gladiolus isn’t flowering well, the first question I ask them is how much sunlight does it get? Not enough is usually the answer!
For more light, try cutting back any vegetation or perhaps an overhanging tree limb, digging up the bulbs, and, if possible, relocating them to a sunnier location in your garden.
Another solution is to plant your gladiolus in pots, so you have a greater range of options for where to put them, such as a sunny patio to promote flowering, which is what you prefer to do.
2. You need to Choose Large, Healthy Corms for Gladiolus to Flower
So, if you’re disappointed at how well your gladiolus is flowering, then I can tell you it might be to do with the size and quality of the corm.
I did some research on this and found out that the size of the corm is important because small corms are not mature and do not necessarily flower the first year until they have grown in size. I personally have observed this phenomenon with my own gladiolus!
What happened with mine is that it grew foliage the first year without flowers and then redirected its energy into growing the corms. This is why corms and bulbs of all species often grow better the second year after planting. So it just takes a little bit of deferred gratification!
I’ve seen that larger bulbs are far more likely to display flowers in their first year, as they are more mature and have more energy to grow and flower in the Spring.
So, if you are buying gladiolus corms in the garden center, do what I do and be a gladiolus bulb connoisseur! Pick up the corms and assess their size and weight. Try to choose the biggest, healthiest-looking bulbs for better flowering in the first year of growth.
3. Have You Planted Your Corms too Deep or too Shallow? How Planting Depth Can Affect Gladiolus Flowering
So, from my research and my own extensive trial and error of planting gladiolus (whilst working as a landscape gardener), your gladiolus should be planted at a depth of around 6-8 inches in the soil.
Why is this the perfect depth for Gladilous?
At this depth, your gladiolus are more insulated from the cold and therefore less susceptible to damage from frost which is one of the most common reasons for not flowering.
The technical explanation is that, if they are planted much deeper, the plant often expends too much energy fighting its way out of the soil, which results in fewer flowers and may cause them to emerge too late to benefit from the hottest and sunniest summer days.
There is also more potential for the bulbs to rot when they are planted too deep in the soil. (Yep, I’ve made this mistake!)
We need to remember that our gladiolus are sensitive to the cold as they are native to arid climates with high temperatures, so if they are planted too shallow, then they are more vulnerable to the effects of cold weather and potentially have less access to resources such as nutrients.
Note that in climates that experience frost (like me!), gladiolus should be lifted from the ground and stored above freezing in dry conditions, such as in a garage. I lift mine gently with a fork out of the ground when temperatures get as low as 41 degrees F (5 degrees C) and wrap them in newspaper and place them in my garage, before replanting them in the Spring when the threat of of frost has gone.
To be honest I now prefer the method of planting my gladiolus in pots so I can just bring the pot into my garage and not have to dig up the corms.
4. Have you Planted too Late? Planting Late in the Season Harms Flowering
Of course our gladiolus bulbs should be planted when the ground has warmed up in the Spring and there is less risk of frost.
Gladiolus flowers are best when they emerge in good, sunny, dry summer weather. If the corm planting is delayed, the gladiolus can emerge as late as fall, when conditions are less favorable. (I’ve done this myself!)
With all the action and activity happening in Spring for us gardeners, I once left my corms in the corner of my garage, and they completely slipped my mind! I planted them at the start of June, and they tried to flower in September when the temperatures were already cooling down!
I can tell you from experience, It can take up to three months for gladiolus to flower after planting the bulbs in the soil.
So, if you plant your bulbs in late May or June, it may be September by the time they flower like mine did.
So I learned my lesson and aim for planting March or April! If you live in a climate where there can be a lot of late frosts that catch your gladiolus out, then I simply recommend planting in a pot and keeping an eye on the forecast; this way, you can retrieve from outdoors your gladiolus if necessary.
I recommend planting your gladiolus as soon as there is a lower risk of frost to give them the time to grow and flower to enjoy in the Summer.
5. Have You Planted Your Corms Too Close? How Far Apart to Plant for Optimal Flowering
Have you made this mistake? Planting your gladiolus bulbs too close together can cause your gladiolus to display fewer flowers.
Think about it like this…each individual corm has to compete with others for space, nutrients, and moisture. When new growth emerges, the foliage also has to compete for sunlight, all of which affects flowering.
I’ve done some experimenting myself, and I can tell you, Ideally, your corms should be spaced at least 8 inches apart. At this distance, there is a good display of flowers and foliage without each gladiolus having to compete for resources.
I’ve tried cramming more into a pot with a distance of 6 or even 4 inches, and to be honest, they do not flower anywhere near as well, and the flowers and foliage were smaller proportionally to how crammed the corms were.
If it is early in the season, you can still dig up the bulbs and space them proportionally, or you can dig them up in the fall and space them further apart to improve flowering which is what I did.
When I spaced mine out the following year they grow much better and I was rewarded with the most gorgeous flowers that had a wonderful aroma! Lesson well and truly learned.
6. Finding the right balance for your Gladiolus…Too Much Fertilizer Can Promote Lots of Foliage with Fewer Flowers
It is true that Gladiolus can flower better with fertilizer (depending on your soil conditions), but from experience, I can tell you that you have to be judicious with how much you feed them. Why? Because too much fertilizer can cause lots of lush foliage to grow at the expense of blooms.
Nitrogen is the nutrient that stimulates foliage to grow (at the expense of flowers) and is found in high quantities in lawn fertilizer.
So, when I worked as a landscape gardener, I once was able to diagnose an unusual reason why my customers’ gladiolus was not flowering. What happened was that the lawn fertilizer (applied by the customer and not me, I hasten to add!) was washed into the surrounding garden borders that contained the gladiolus after rainfall, and the added nitrogen concentration caused lots of green growth with no blooms.
Once this has happened to your gladiolus there is not much you can do to promote flowering this year other than scale back the use of fertilizer.
However, there is no reason the gladiolus shouldn’t flower well the following year. The gladolus in question did flower well the following year, but without an added fertilizer.
I find the best balance is to apply gradual release granule fertilizer in the Spring.
7. Is Your Soil Low in Nutrients? Create the Right Soil so Your Gladiolus Can Flower
So, the reason your gladiolus isn’t flowering may well have to do with your soil. Gladiolus tends not to display as many flowers if they are planted in sandy, nutrient-poor soil, as they do not have the resources required for flowering. I noticed myself when I was landscape gardening in a client’s gardens.
Gladiolus grows relatively quickly in the Spring and Summer when the foliage emerges and the flowers develop, which requires nutrients.
So, how do you promote gladiolus flowers?
- Plant your corms in good soil, ideally amended with compost, leaf mold, or well-rotted manure for a good balance of nutrients and to ensure a well-draining soil structure so that the corms do not rot.
- Use a well-balanced granular fertilizer in the Spring when the gladiolus foliage begins to emerge in the Spring or a tomato feed. Applying fertilizer at half strength provides the gladiolus with the nutrients it requires without actually harming flowering because of too much nitrogen. I’ve been recently experimenting with Tomato feeds this year for feeding my flowering plants as it has proportionally less nitrogen than most fertilizer. I’ll update this article with a recommendation if my gladiolus have a better display of flowers!
- So this was a tip I acquired from British gardener Monty Don: Keep on feeding the green foliage of your gladiolus after the flowering with fertilizer every two weeks with liquid seaweed. After flowering the foliage is storing energy from the sun and from nutrients in the soil to store in the bulbs for next year’s flowers. Feeding the gladiolus ensures that the bulb can store enough energy for the following year’s display of flowering.
If you follow these steps, you can significantly increase the size of the foliage and the number of gladiolus flowers on display.
8. Protect Your Corms! Frost Damage Prevents Flowering (Gladiolus are Frost Sensitive)
As we discussed, gladiolus are native to warm climates such as South Africa and the Mediterranean region of Europe which experience mild Winters.
If your gladiolus have not flowered this year then I’m afraid there is a good chance they have suffered from frost damage over the Winter, particularly if they are in pots or planted too shallow in the soil.
Gladiolus corns are frost sensitive, so it is important to take this into account when growing gladiolus.
This can of course depend on how you treat gladiolus as I have seen some people who live in cold climates regard them as an annual flower with the expectation of only flowering one year whereas in reality, in the right climate they are perrenenial corms that reemerge every year.
As gladiolus is a perennial flowering plant, to survive Winter they should either be:
- Planted in pots so that you can bring them indoors over Winter to avoid frost (which is what I now do as, in my opinion, it is much easier).
- Dig the bulbs out of the soil carefully in the Fall to be stored over Winter and replanted again in the following Spring once there is less risk of frost.
I should warn you even if you are in a climate that doesn’t experience frost, leaving gladiolus in the ground over also Winter increases the risk of rot and fungal disease.
In the US gladiolus are hardy in zone 8 but require digging up and storing over Winter in Zones 7 or colder. As I talked about, I store my corms in a cool garage that is free from frost in a dry paper bag or newspaper, which lowers humidity.
Pro Tip: Regardless of the climate, I’ve found that it is a good idea to cover gladiolus bulbs in a layer of mulch (such as compost, or straw) as this helps to insulate them from a late frost, which sometimes catches me out when I planted my corms in flower beds and boarders.
Are you planning on planting your gladiolus corms in pots so you can move them indoors? I recommend plastic pots for this as they are much lighter then clay, ceramic or terracotta pots. Keep in mind the pot is going to be full of soil and potentially damp so they can get very heavy if you need to move them!
9. You Need Well-Draining Soil for Your Gladiolus to Flower
Gladiolus originates in South Africa and the Mediterranean where it grows in well-draining and moderately fertile soil.
Therefore, gladiolus does not grow well in boggy soils or clay soils that retain too much water.
In slow-draining soils, the corns of the gladiolus often rot or suffer from a fungal disease that prevents the corn from growing and the gladiolus does not grow or flower.
Even if the gladiolus does start to grow, in my experience, the stress from being in saturated soil can prevent it from displaying flowers.
So, how do we solve this?
It is therefore it is essential to plant gladiolus in soil that that replicates their native conditions.
So, I was taught the ideal this potting mix from more experienced galdiolus growers whiclst working at a garden center. Gladiolus corms should be planted in soil that has been amended with leaf mold, compost, or well-rotted manure with some horticultural grit or perlite mixed in for additional drainage.
I learned that this provides the right soil profile with lots of nutrients for growth but, balanced with the drainage required.
I want to just remind you that Gladiolus should be planted 8 inches so make sure that you work the grit into the soil so that all the soil surrounding the moisture-sensitive corn is well draining.
As you can imagine, another option to ensure gladiolus flowers for gardens with boggy soil is to grow gladiolus in pots or containers, which is definitely my preferred
With pots, you can create the optimal soil mix with some compost and grit or perlite tailouring the soil conditions to the gladiolus preference perfectly, which (I can tell you from experience!) is much easier than amending garden soil in borders.
Gladiolus is much more likely to flower in soil that emulates their preferred conditions in their native home range so well-draining soil amended with compost provides the best conditions for flowering gladiolus.
10. Are You Watering Too Often? How Overwatering Can Affect Flowering
We need to remember gladiolus is more often affected by overwatering than underwatering as they are native to Africa and the Mediterranean where they have adapted to the dryer conditions with lower levels of rainfall.
Watering gladiolus too frequently can increase the risk of rot or disease, particularly if the soil is not well draining.
I have lived in many different climates, from California to the rainy Pacific northwest, and in my experience, in most climates, gladiolus do not require any additional water, If they are planted in flower beds however, they do appreciate a good soak if there has been excessive drought whilst the new green leaves are emerging or you have planted in pots.
In this case you should soak the ground once per week rather than water a little and often.
This is best practice for watering as the corms has all the moisture required for growth but the soil is allowed to dry out somewhat between bouts of watering to mitigate the risk of rot.
Pro tip: Planting your corms in pots? Keep in mind that terracotta and clay pots are porous which means on a hot day they dry out much quicker. I plant my corms in ceramic pots as this means the soil dries out at a more reasonable rate, allowing the corms to benefit from the moisture in the soil rather then the soil drying out in a day which can happen with clay and terracotta pots on hot days.
Just keep in mind when planting gladiouls, in damp ground, the gladiolus corms either suffers from disease or the stress of being in boggy soil reduces the flowering display as it is contrary to their preferred slightly dryer soil conditions that they thrive in their native range.
11. Insect Damage? Could Gladiolus Thrips be Preventing your Gladiolus from Flowering
The enemy of your gladiolus is a small insect that feeds on the sap of flowers and leaves called the Gladiolus thrip.
I must warn that thrips can also affect other flowering bulbs in your garden, such as lilies and irises.
The symptoms of the gladiolus thrips are small white marks on your leaves and flower buds that do not open.
The best course of action is to use an insecticide which is available from garden centers or online. From my experience, these treatments may take repeat applications to prevent further damage to your gladiolus.
Do you have any more questions about your Gladilous? Please leave a comment below, and I’ll reply! I’d love to hear from you!
Key Takeaways:
- The most common reasons for gladiolus not flowering are because of too much shade, too much fertilizer, frost damage, and slow-draining soils which cause the bulb to rot rather than flower. Gladiolus thrip feeds on sap which can harm flower buds.
- Gladiolus takes up to three months to flower after planting.
- Gladiolus requires well-draining soil and full sun with moderate amounts of water to flower.
- Gladiolus bulbs are sensitive to frost. Dig up the bulbs in the Fall to prevent frost damage or plant gladiolus in pots and store them in a garage over Winter.