Alliums do not flower if the bulbs are not fully mature, planted too shallow, overcrowded or stored for too long before planting. Alliums also do not flower when planted in slow draining soil and tend not to bloom if growing in full shade.
Most of the reasons for non flowering alliums are in some way to do with the bulbs, whether its the quality of the bulb or how they are planted, however there are also some environmental factors that can prevent alliums from flowering.
Keep reading to for an explanation of why your allium is not flowering and how you can solve the problem so that the alliums flower the following year…
Size of Bulb Affects Flowers (Small Bulbs May not Flower the First Year)
One of the key factors for alliums to flower in the first year of planting is the size and maturity of the bulb.
It takes a lot of energy for a plant to flower, so if the bulbs are smaller then there is less energy and resources available for flowering.
Small or low quality bulbs generally spend the first year redirecting there energy from flowering to growing, adjusting to the new soil conditions and establishing properly and can potentially flower the following year as they mature.
The bigger more mature bulbs have a much better prospect of flowering compared to smaller bulbs as they have more energy stored up ready to grow in the Spring.
If you have just planted your allium bulbs and there are no flowers in the first year then they are more likely to flower they following year.
However when selecting allium bulbs (or any bulb) at the garden centre always make a concerted effort to choose the biggest most mature bulbs available to ensure a greater chance of flowering and a healthy plant.
Planting Allium Bulbs at the Wrong Time Can Prevent Flowering
The optimal time for planting alliums bulbs so that they flower is in the Fall in September and as late as November, whilst the ground is still warm and before freezing temperatures.
If alliums bulbs are planted too late in the year then there is an increased risk of the bulb rotting in the ground and not growing or flower in the Spring.
It is possible to plant allium bulbs in the Spring but it is more likely to redirect its energy to establishing in the new soil rather then flowering, however with patience the allium should flower well the following year as it has had a lot of time to establish.
Bulbs are Too Crowded For Alliums to Flower
A common mistake when planting allium bulbs is planting the bulbs too close together which can prevent them from flowering.
If allium bulbs planted too close then they have to compete with each other for space, sunlight, nutrients and moisture which can result in bulbs that do not have enough resources for flowering.
To improve the prospect of flowering for the next year you have to dig them up and space the bulbs appropriately.
The optimal spacing for allium bulbs is around 8 inches apart. At this distance they are close enough to for a nice display but each bulb has enough space for the resources required for flowering.
If you suspect the reason for your alliums not flowering is because of overcrowding, then dig the bulbs up (ideally in the Fall) and give each bulb the appropriate amount of space and the allium should flower the following year.
Planting Depth of Bulbs can Influence Flowering
The optimal planting depth for allium bulbs depends on the size of the bulb with larger more mature bulbs benefiting from deeper planting and smaller bulbs benefiting from comparatively shallow planting.
According to the RHS the best planting depth is 4 times the diameter of the bulb which is frequently around 8 inches or so.
If bulbs are too shallow then they are vulnerable to frost damage in the Winter which damages the bulb and prevents the allium from flowering.
Storing Bulbs For Too Long Prevents Flowering
The bulbs of the allium are full of the energy they require for flowering.
Bulbs can be stored for around 12 months before planting but if they have been kept in storage for longer then 12 months or have been stored in less the ideal conditions then the quality of the bulb can decrease as its resources deplete over time which can prevent flowering.
Allium bulbs that have been in storage for a long time may require 2 years in the ground before they display flowers, however if stored badly they may not flower at all.
Bulbs that have frozen in Winter or have been exposed to heat in Summer whilst in storage are less likely to flower.
Allium bulbs are best stored in a cool place such as garage so they can stay dormant, and where they are unlikely to freeze in Winter or heat up too much in Summer before planting (The best time for planting allium bulbs is the early Fall).
Consider that the bulbs may have been in storage for some time at a garden center so try to buy your bulbs from a store with a good reputation for quality so that your allium bulbs can flower in the first Spring after planting.
Allow Foliage to die off Rather then Cut Back to Improve Flowering
A common mistake with alliums (and other plants such as irsis) is cut back the foliage once the flowers have faded so that the garden boarder looks tidy rather then just the leaves and stems that eventually turn yellow as the die off.
The time after flowering, the foliage of your allium is still absorbing sunlight for photosynthesis and drawing up nutrients and moisture from the soil for energy, which is then stored in the bulb so that following years flowers have all the resources they require for growing and flowering in the Spring/Summer.
Cutting away the foliage means that there is less time for the bulb to store energy in the bulb so next years flowering can be underwhelming or the bulb may not flower at all.
To really ensure the best possible flower display for the following year it is best practice to deadhead the faded flowers (so your allium does not expend its energy producing seed) and to leave the green foliage in place until it has turned brown in the Fall or Winter.
This way the foliage part of the allium can use the late Summer and Fall to store all the energy for next years flowers.
Some gardens recommend that the post flowering time is the best time to apply a natural fertilizer such as liquid seaweed, so that the bulb has additional nutrients to draw upon so that it grows and matures ready to display flowers next year, however with the right soil this is not always necessary.
Once the foliage has died back then it can be cleared and composted so that your garden boarder looks tidy for Winter and the following Spring.
Too Much Nutrients Prevents Alliums Flowering
Allliums prefer soil that is well draining and not overly rich in nutrients before flowering. If you apply additional fertilizer or mulch the ground with organic matter that is high in nitrogen (such as poultry manure) then your alliums may have lots of lush foliage but few flowers.
Nitrogen is a key nutrient for all plants but too much nitrogen can promote foliage growth at the expense of flowers.
To avoid this happening to your alliums, avoid adding any fertilizer to the ground until after the flowering season (alliums flower in the Spring and Summer but exact time can vary according to specific cultivars and conditions).
Alliums grow and flower best in well draining often gritty soil mix with good multi purpose compost.
Therefore an abundance of nutrients before Spring and Summer is not favourable for displaying flowers.
If you have added fertilizer to your alliums there is not much you can do other then scale back any use of fertilizer mulch, ensure the soil is well draining and wait until the following year by which time the nutrient profile of the soil should be more balanced and the alliums can flower.
Boggy Soil Can Prevent Alliums From Flowering
Alliums are native to regions with dry sandy soils such as Central Europe and Persia so they require well draining soil if they are to survive Winter without rotting and for flowering in the Summer.
In slow draining or boggy soils the allium bulbs tend to rot and not grow let alone flower, so if your soil is…
- Heavy or compacted clay soil.
- Low lying naturally boggy soil.
…then the best option is to plant (or transplant) allium bulbs in pots, container or raised beds to grow alliums for flowering.
It is much easy to create a good potting mix and grow alliums in pots then it is to amend garden boarders to suit alliums.
When planting in pots it is best practice to add some horticutral sand or grit (around 15% by volume) to ensure drainage with the rest as multi purpose compost for the optimal balance of good drainage and soil nutrients for alliums to display flowers.
Pots also have the advantage of being portable so if there is excessive rain you can place the pots and containers under cover to prevent allium bulbs from rotting in saturated soil.
For alliums in garden boarders, it is a good idea to prepare the soil by amending with sand or grit to replicate the sandy, well draining conditions in which alliums thrive.
Not Enough Light for Alliums to Flower
Alliums thrive in full sun and generally flower best in at least 6 hours of direct sun.
In hot climates or in years with significant heat waves, alliums can benefit if they are located in 6 hours of morning sun with shade in the midday and afternoon to protect them from intense heat that could result in drought and wilting which can of course affect flowering.
Alliums can flower in partial shade but if alliums are in too much shade then they are not likely to flower to their best and it to transplant them but lifting the bulbs carefully with a fork and finding a sunnier location for them.
If possible try to cut back over hanging tree limbs that may have formed a dense canopy and cast shade on your alliums or cut back any surrounding vegetation that may be crowding your alliums.
With more hours of sun the allium has more energy and resources to display flowers.
Drought Can Affect Alliums Flowering
Alliums prefer soil to be well draining (it is a good idea to add some grit when planting bulbs to ensure good soil drainage around the bulbs) but they can suffer in a drought.
If conditions are too dry then the allium in the Spring and Summer then the allium may not flower or produce an underwhelming display of flowers.
If conditions are persistently dry in the Fall when alliums are storing energy for next years flowers in their bulbs then this can also prevent a good display of flowers the following year.
Alliums are low maintenance most of the year but if there is a significant drought in Spring, Summer or Fall then give the soil a good soak once a week to ensure the bulbs can draw upon the moisture when required.
Do not water in Winter as the bulb is in a state of dormancy and excess water can increase the risk of rot.
Potted alliums tend to be at greater risk of drought then bulbs planted in garden boarders. so water the bulbs once a week consistently if there has been dry weather to promote flowering in the Spring.
- The reasons alliums do not flower is usually because the bulb is not yet mature, planted too shallow, or planted at the wrong time of year. Drought, lack of sun and boggy soil can also prevent alliums from flowering.
- Alliums require planting in gritty, well draining soil and to grow in full sun to have enough energy to flower.
- Soil that has been amended with manure or has had nitrogen fertilizer often promotes foliage growth at the expense of flowers.
- Cutting back the foliage too early whilst it is still green in the late Summer and Fall can prevents the allium from feeding the bulb with nutrients, moisture and energy for next years flowers. Only cut back foliage once it turns brown.