Gladiolus does not flower when planted in too much shade, damp soil or if it has suffered from frost damage the previous Winter. Gladiolus requires well draining soil and Winter protection to flower properly. Too much fertilizer can also prevent gladiolus from flowering.
Gladiolus typically take around 2-3 months from planting the bulbs (known as corms) to displaying flowers. Flowering is often weather dependent with heavy rain and overcast days during Summer resulting in far fewer flowers.
Keeping reading to establish the cause of why your gladiolus and how to promote gladiolus flowering…
Too Much Shade for Gladiolus to Flower
All gladiolus varieties require a location of full sun with 6 hours or more of direct light.
Gladiolus grow in open meadows in South Africa and Mediterranean countries in Europe where they enjoy full sun and flower gloriously.
Whilst you do not need to live in a Mediterranean climate it is important to plant your gladiolus in the sunniest area of your garden so that the gladiolus has enough energy to flower.
The amount and intensity of sunlight is directly correlated with the display of flowers in the summer.
If your gladiolus is not flowering a lack of sun is usually the cause.
Try to cut back any vegetation or perhaps an overhanging tree limbs for more light or dig up the bulbs are relocate them if possible to a sunnier location of your garden.
Another solution is to plant you gladiolus in pots so you have a greater range of options for where to put them such as a sunny patio to promote flowering.
Bulb Size can Influence Flowering
If you gladiolus is not flowering well is not flowering well then this could be because the size and quality of the bulb.
The size of the bulb is important because small bulbs are not mature and do not necessarily flower the first year until they have grown in size.
Instead they often grow foliage the first year without flowers and redirect their energy into growing the bulb. This is why bulbs of all species often grow better the second year after planting.
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.
If you are buying gladiolus bulbs in the garden center try to choose the biggest, healthiest looking bulbs for better flowering in the first year of growth.
Planting Depth Can affect Gladiolus Flowering
Gladiolus should be planted at a depth of around 6-8 inches in the soil.
At this depth the 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.
If they are planted much deeper then often the plant 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 days of Summer sun.
There is also more potential for the bulbs to rot when they are planted to deep in the soil.
Gladiolus are sensitive to the cold as they are native to arid climates with high temperatures so if they are planted to shallow then they are more vulnerable to the affects of cold weather and potentially less access to resources such as nutrients.
Note that in climates that experience frost gladiolus should be lifted from the ground and stored above freezing in dry conditions such as a garage.
Planting Late in the Season Harms Flowering
Gladiolus bulbs should be planted when the ground has warmed up in the Spring and there is less risk of frost.
Gladiolus flower best when they emerge in good sunny, dry weather in the Summer. If planting of bulbs is delayed then the gladiolus can emerge when conditions are less favorable and be as late as Fall.
It can take up to three months for gladiolus to flower after planting the bulbs in soil.
So if you plant your bulbs in late May or June it may be September by the time they flower.
Plant you gladiolus as soon as there is lower risk of frost to give them the time to grow and flower to enjoy in the Summer.
Gladiolus Bulbs too Close Together Reduces Flowers
Planting you gladiolus bulbs too close together can cause your gladiolus to display fewer flowers.
This is because each individual bulb has to compete with one anther for space, nutrients and moisture. When the new growth emerges the foliage also has to compete for sunlight, all of which affects flowering.
Ideally bulbs 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.
If it is early in the season you can still dig up the bulbs and space them proportionally or dig them up in the Fall and space them further apart to improve flowering.
Too Much Fertilizer Promotes Gladiolus Foliage with Fewer Flowers
Gladiolus can flower better with fertilizer (depending on your soil conditions) but you have to be judicious with how much you feed gladiolus as 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 and is found in high quantities in lawn fertilizer.
A common reason for gladiolus not flowering is that the lawn fertilizer is washed into the surrounding garden boarders after rainfall and the added nitrogen concentration causes 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 then scale back the use of fertilizer.
However there is no reason the gladiolus shouldn’t flower well the following year.
Nutrient Poor Soil can Prevent Flowering
Gladiolus tend 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.
Gladiolus grows relatively quickly in the Spring and Summer when the foliage emerges and the flowers develop which requires nutrients.
To promote gladiolus flowers:
- Plant your bulbs 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 bulbs does not rot.
- Use a well balanced liquid fertilizer applied at half strength once every 2 weeks when the gladiolus begin 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. Tomato feeds are an excellent option for feeding flowering plants as it has proportionally less nitrogen then most fertilizer.
- Keep on feeding the green foliage of your gladiolus after the flowering with fertilizer every two weeks. After flowering the foliage is storing energy from the sun and from nutrients in the soil to store in the bulbs for next years flowers. Feeding the gladiolus ensures that the bulb is able to store enough energy for the following years display of flowering.
Frost Damage Prevents Flowering (Gladiolus are Frost Sensitive)
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 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.
As gladiolus is a perennial flowering plant, to survive Winter they should either be:
- Planted in pots so that you can bring them into a indoors over Winter to avoid frost.
- 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.
Leaving gladiolus in the ground over 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. Store in a cool garage that is free from frost in a dry paper bag which lowers humidity.
Regardless of the climate it is a good idea to cover gladiolus bulbs in a layer of mulch (such as compost, or straw) to help insulate them from a late frost.
Slow Draining Soils Can Prevent Flowering
Gladiolus originates South Africa and the Mediterranean where it grows in well draining soil that is moderately fertile.
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 which prevents the corn from growing and the gladiolus does not grow or flower.
Even if the gladiolus does start to grow, the stress from being in saturated soil can prevent it from displaying flowers.
Therefore it is essential to plant gladiolus in soil that that replicates their native conditions.
Gladiolus corns 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.
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.
Another option to ensure gladiolus flower for gardens with boggy soil to grow gladiolus in pots or containers.
With pots you can create the optimal soil mix with some compost and grit or perlite which is much easier then amending garden soil in boarders.
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.
Watering too Frequently can Affect Flowering
It is important to remember with gladiolus that they are more often affected by over watering then under watering 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.
In most climates gladiolus do not require any additional water, however they do appreciate a good soak if there has been excessive drought whist the new green leaves are emerging.
In which case you should soak the ground once per week rather then water little then often.
This is best practice for watering as the bulb 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.
In damp ground the gladiolus bulb either suffers from disease or the stress of being in boggy soil reduces the flowering display as it is contrary their preferred slightly dryer soil conditions that they thrive in their native range.
The enemy of your gladiolus is a small insect that feeds on the sap of flower and leaves called the Gladiolus thrip.
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 a insecticide which are available from garden centers or online . These treatments may take repeat applications to prevent further damage to your gladiolus.
- The most common reasons for gladiolus not flowering are because of too much shade, too much fertilizer, frost damage and slow draining soils which causes the bulb to rot rather then flower. Gladiolus thrip feeds on sap which can harm flower buds.
- Gladiolus takes up to three months to flower after planting.
- Gladiolus require 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 in a garage over Winter.