Have you planted your allium bulbs, anticipating a gorgeous floral display only to be greeted by some limp foliage or perhaps no growth at all? I know firsthand that planting bulbs can be tricky, but fortunately, I have a lot of experience in growing alliums myself (with some trial and error!!), and I’ve researched all the tips to get them to flower!
In this article, I’ll distill everything that I’ve learned from growing alliums, focusing specifically on how to pinpoint the reason your alliums are not blooming and the methods I use myself to help them flower.
Do you want the short answer?
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.
In my experience, most of the reasons for non-flowering alliums are related to the bulbs, whether it’s the quality of the bulb or how they are planted. However, some environmental factors can prevent alliums from flowering.
Keep reading 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)
So I am now a bit of a bulb connoisseur! Whenever I am in a garden center buying bulbs I take time to study them and really assess their health. Why, you ask? One of the key factors for alliums to flower in the first year of planting is the size and maturity of the bulb.
From research, the explanation behind this (which is quite logical) is that it takes a lot of energy for a plant to flower, so if the bulbs are smaller, then there is less energy and fewer resources available for flowering. Makes sense, right?
But you can have success with smaller bulbs as I have. You just need to know that small or low-quality bulbs generally spend the first year redirecting their energy from flowering to growing, adjusting to the new soil conditions, and establishing properly, and can potentially flower the following year as they mature.
I can tell you from personal experience the bigger, more mature bulbs have a much better prospect of flowering compared to smaller bulbs as they have more energy stored up and ready to grow in the Spring.
But I must say, as a general rule, if you have just planted your allium bulbs and there are no flowers in the first year, then they are more likely to flower the following year, which I have found holds true even if you have been discerning about your bulb choice.
However, when selecting allium bulbs (or any bulb) at the garden center, I recommend always making a concerted effort to choose the biggest, most mature bulbs available to ensure a greater chance of flowering and a healthy plant.
I have seen for myself the difference bulb size can make, and the larger bulbs always have a better floral display!
Planting Allium Bulbs at the Wrong Time Can Prevent Flowering
Have you planted your bulbs in Spring or Winter? I actually consulted with a horticulturist for advice on this, and she told me that the optimal time for planting allium 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.
She explained to me that if allium bulbs are planted too late in the year, there is an increased risk of the bulb rotting in the ground and not growing or flowering in the Spring. I have found this to be particularly true in gardens with slow-draining soil, such as clay soil.
Of course, you can plant allium bulbs in the Spring, but the caveat I have to this is that it is more likely to redirect its energy to establishing in the new soil rather than 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
I thnk this is a mistake that every gardener makes at some point! Have you been guilty of trying to cram too many bulbs in to get as many flowers as possible? A common mistake when planting allium bulbs is planting the bulbs too close together, which can prevent them from flowering.
Why is this? Well, if allium bulbs are planted too close, then they have to compete with each other for space, sunlight, nutrients, and moisture, which can result in individual bulbs that do not have enough resources for flowering.
So we’ve planted the bulbs too close together, what do we do now? To improve the prospect of flowering for the next year, you have to dig them up and space the bulbs appropriately.
I’ve discovered through some trial and error that the optimal spacing for allium bulbs is around 8 inches apart. At this distance, they are close enough for a nice display, but each bulb has enough space for the resources required for flowering. It’s all about finding that happy balance for your allium bulbs!
If you suspect the reason for your alliums not flowering is because of overcrowding, then I would 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.
I would also give them a good amount of compost or well-rotted manure to add nutrients to the soil, which I’ve found effective at increasing flowering.
Planting Depth of Bulbs Can Influence Flowering
So this one is a bit more tricky as you have to judge for yourself. 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, but I would use 8 inches as a guideline and actually measure the diameter of the bulb and plant it that way.
So the rationale behind planting at this depth is to give the bulb enough insulation from the soil to prevent them from freezing, but not planting too deep so that your bulbs are going to expend most of their stored energy growing to the surface rather than putting that energy into flowering.
I have been to gardens where they plant their bulbs too shallow, and the bulbs have just frozen and rotted in Spring. I find this can happen when bulbs are in pots as they have less insulation from the soil.
Pro tip: Are you planting allium bulbs in a pot? Then, I recommend choosing a thicker ceramic pot rather than a thin plastic pot for more insulation for the bulbs in winter. In really cold climates, in my opinion, the best thing to do is to wrap your pot in insulating fleece to protect your bulbs for your allium can flower.
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, so I recommend digging them up again in the Fall (to minimize stress) and inspect the bulbs…are they still firm? In which case, I’d replant them at the proper depth, but if they feel mushy or look damaged, then buy some more bulbs and plant them deeper than before to ensure flowering.
Storing Bulbs For Too Long Prevents Flowering
As we discussed, the bulbs of the allium are full of the energy they require for flowering.
So, from my research, your bulbs can be stored for around 12 months before planting but if they have been kept in storage for longer than 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.
However, I discovered that they can still flower, although allium bulbs that have been in storage for a long time may require 2 years in the ground before they display flowers; but, if stored badly, they may not flower at all.
It can be from either extreme of temperature. Bulbs that have frozen in Winter or have been exposed to heat in Summer whilst in storage are less likely to flower.
So how do we store excess bulbs? Allium bulbs are best stored in a cool place such as a 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).
Important Tips: I place them in a cardboard box to minimize the amount of moisture around the bulbs, which can spoil them. I would advise you not to keep your bulbs in plastic bags as this traps humid air and condensation, which can spoil your bulb.
I recommend researching the reputation of your garden center or online seller before buying bulbs!
We need to 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 than Cut Back to Improve Flowering
So this is, in my opinion, the best tip of them all to get your alliums flowering, and it’s a mistake I see everyone make! The mistake that I’m talking about with alliums (and other plants such as iris) is to cut back the foliage once the flowers have faded so that the garden border looks tidy rather than just the leaves and stems that eventually turn yellow as they die off.
Are you guilty of this as a tidy gardener?!
Here is what we need to undertsand…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 in following years, flowers have all the resources they require for growing and flowering in the Spring/Summer.
When we cut away the foliage, it means that there is less time for the bulb to store energy in the bulb, so next year’s flowering can be underwhelming, or the bulb may not flower at all.
So what do we do?
I can tell you firsthand that 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 be used in late summer and fall to store all the energy needed for next year’s flowers.
Pro Tip: So you want to go the extra mile to get your alliums to flower? After flowering water your allium leaves with a liquid seaweed feed. This ensures that your bulb has the nutrients it needs to draw upon so that it grows and matures, ready to display flowers for next year. I tried this myself and the result was that I had my best year for allium flowers!
The reason liquid seaweed works is that it is organic and has the right balance of nutrients for your bulbs, with having such a high concentration of nutrients that it harms the bulb (it’s a balancing act!)
Too Many Nutrients Prevents Alliums Flowering
So we just talked about feeding alliums with liquid seaweed, but when about adding fertilizer before they flower?
Well, the truth is that alliums prefer well-draining soil that is not overly rich in nutrients before flowering, so if we 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, which is the exact opposite we are after with our alliums!
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 the exact time can vary according to specific cultivars and conditions).
I have grown alliums for years and my alliums grow and flower best in well-draining, often gritty soil mixed with good multi-purpose compost.
Therefore, an abundance of nutrients before spring and summer is not favorable for flower display.
If you have added fertilizer to your alliums, there is not much you can do other than scale back any use of fertilizer, 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.
As I mentioned, I would also avoid using poultry manure as a mulch as it’s too high in nitrogen. I personally just use compost or occasionally well-rotted horse manure (which has a lower level of nitrogen than poultry manure). I only use the manure mulch typically if the soil is particularly poor (if it is sandy, for example) and needs nutrients added to it.
Boggy Soil Can Prevent Alliums From Flowering
So, for us to grow alliums properly, we need to consider how they grow naturally. 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, containers, or raised beds to grow alliums for flowering.
In my opinion, planting your alliums in a pot is best because it is much easier to create a good potting mix and grow alliums in pots than amending garden borders to suit alliums. (I can tell you from experience that amending heavy clay soils is incredibly hard to do!)
When planting in pots, it is best practice to add some horticultural 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. I personally prefer to use grit as it creates a more porous soil mix than sand, which my allium bulbs seem to enjoy more from my observations.
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.
Helpful Tip: Do you live in a rainy climate? If excess rainfall is a problem in your climate, I like to put my bulbs in a clay or terracotta pot, which is more breathable than plastic, so the soil dries more evenly. I also place my pots on ‘feet’ to elevate them off the ground to create more airflow and ensure good drainage from the base of the pot to mitigate soggy soil. This stops your bulbs from rotting and ensures your bulbs can flower.
For alliums in garden borders, I dig to at least 18 inches to prepare the soil (if it is poor draining). I add about 20% grit to the soil (by volume) to increase drainage. This creates the sandy, well-draining conditions in which alliums thrive.
Not Enough Light for Alliums to Flower
Remember we talked about how alliums grow in their natural environment? Well, our alliums thrive in full sun and generally flower best in at least 6 hours of direct sun.
I used to live in a really hot climate in California, which, as you can guess, is significantly hotter than its natural environment. If I had placed my alliums in full sun in this climate, the heat would have prevented my alliums from flowering to other best. So I did a little testing each year and found that my alliums grew best when in morning sun followed by afternoon shade. Why?
Because my alliums were able to benefit from the 6 hours of sunlight in the morning, but they were shaded during the hottest part of the day to prevent the allium from having to contend with the stress of being too hot.
So I recommend that you do the same if you are in a hot climate, but in cooler climates you can generally get away with planting them in full sun at any time of day.
Your alliums can flower in partial shade, but if they are in too much shade, they are not likely to flower at their best, so you need to transplant them by lifting the bulbs carefully with a fork and finding a sunnier location for them, or you can put them in a pot which gives you more options of where to put them, on a sunny patio for example!
When I worked as a landscape gardener, sometimes I would try to cut back overhanging tree limbs that may have formed a dense canopy and cast shade on the alliums or cut back any surrounding vegetation that may be crowding the alliums.
From my observations, sunlight is probably the most important factor for alliums to flower, and with more hours of sun, the allium has more energy and resources to display flowers.
Drought Can Affect Alliums Flowering
As we have discussed, 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 from drought.
From my own observations, if conditions are too dry, then the allium in the spring and summer may not flower or produce an underwhelming display of flowers.
But is it also not just spring and summer we have to think about.
If conditions are persistently dry in the Fall when alliums are storing energy for next year’s flowers in their bulbs, then this can also prevent a good display of flowers the following year. I have been personally disappointed when this happened to me!
My alliums were not as good as I anticipated and I only realized that the dry Fall the previous year was the problem after doing some research of my own and speaking to some experts! There is always something to learn in gardening!
Alliums are low maintenance most of the year, but if there is a significant drought in Spring, Summer, or Fall, I now give the soil a good soak once a week to ensure the bulbs can draw upon the moisture when required.
Of course, I should caution to not water in Winter as the bulb is in a state of dormancy and excess water can increase the risk of rot.
I would also like to highlight that potted alliums tend to be at greater risk of drought than bulbs planted in garden boarders, so water the bulbs consistently once a week if there has been dry weather to promote flowering in the spring.
Important Tip: If you are growing alliums in a pot in a hot climate, I find that it’s better to plant them in plastic or ceramic pots. Plastic retains moisture better, so your pot won’t dry out in the sun as quickly. Your allium bulbs are also less likely to suffer drought, which means they can flower in the Spring! I would avoid clay and terracotta pots in hot climates, as these would dry out too quickly in hot climates.
Success Tip: Are you concerned about drought affecting your allium flowering? Use a larger pot if as they have more capacity for soil and, therefore, can hold more moisture. This prevents the soil from drying as quickly, and your allium can flower to its potential.
Do you have any questions or insights about allium flowering? Please leave me a comment below, and I’ll reply! I love hearing from you and hearing different perspectives when it comes to gardening!
Key Takeaways:
- The reasons alliums do not flower are 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 while it is still green in the late Summer and Fall can prevent the allium from feeding the bulb with nutrients, moisture, and energy for next year’s flowers. Only cut back foliage once it turns brown.