Did you enjoy your ball-like decorative allium blooms this year? From white to burgundy via blue and all shades of purple, from small to 12-inch large, their inflorescences are hard to miss in a garden… But my real question is: do you want another spectacular floral display from these rewarding bulbous perennials next year?
Then you need to care for your alliums now, in early summer, around June, when their blooms have done their job, or you may be disappointed when spring comes back…
I know, “Once you plant alliums, you can forget them and they will come back year after year,” you might have heard, and it is partially true – but not fully.
Let’s talk about it; you need to understand what happens to your alliums at the end of their glorious flowering season.
Alliums are bulbous perennials, and they have a different vegetative cycle from other plants. They “wake up” in spring and then “go to bed” (dormancy” by late spring or early summer. They spend the rest of the year underground, as large bulbs, alive but asleep – like animals that hibernate.
Alliums start going into dormancy as soon as their blooms are spent. But they do it slowly, because first, after the flowering effort, they need to “recover” and store nutrients fin their bulbs for next year.
This is why the “after flowering period” is very delicate and important for next year’s blooms and this is why I want to tell you what you need to do, and mistakes to avoid…
1. Cut the Dead Flowering Stem – But Wait!
Once your alliums have flowered, it has an option… “Shall I propagate by seed or by bulb?” You need to help him make the right choice, which is the latter for you… If you allow flowering perennials to produce seeds, they will invest a lot of energy into growing them, taking it from their “underground food pantries”.
You will end up having smaller bulbs, hence lesser floral displays (if at all), and to propagate alliums by seed it will take you at least two years before you see even a small blossom.
So, you will have to cut the bloom, but not immediately. Wait till the stem loses color or turns yellow(ish), then prune it back to ground level.
“Why should I wait,” you may ask? Because the stem is still photosynthesizing, and the allium’s bulb needs all the energy it can get at this stage.
“Can I still snip off the flower head as soon as it wilts? It looks ugly in my garden!” Yes, you can, it’s not ideal, but feel free to do it.
2. Feed Your Alliums – Promptly and Repeatedly
When the blooms of your alliums are spent, you have 6 to 8 weeks before the leaves die off and the plant goes into dormancy. And in this period, you want to get as fat a bulb as possible if you want big blooms next year.
So, I suggest you use a liquid, fast-release natural fertilizer, because a slow-release one would take too long.
And you want a low nitrogen fertilizer, because you don’t want leaf growth, but bulb growth. I suggest an NPK 5-10-10 or 4-10-6 every 2 weeks. However, it would be even better if you fed your alliums more often but with lower nutrient levels, for steadier growth so, NPK 3-7-5 on a weekly bases in this case.
You can add a bit of compost (a cup per plant or a 1-inch layer, 2.5 cm) to back up your liquid fertilizer with a “fuller balanced diet”, i.e. more nutrients, and there are some other natural products you can use to boost the bulb’s growth and health even more…
- Bone meal; it is rich in phosphorus and excellent to fatten bulbs. Use 1 to 2 tablespoons per plant if it is a small or medium variety; otherwise, for large ones scatter it in a circle 4–6 inches (10–15 cm) from the stem and lightly scratch it into the soil.
- Wood ash; it is low in nitrogen and high in potassium and lots of trace elements; it is like a “medicine” for bulbs, great for their health, and it also helps sterilize the soil. Use little, 1 to 2 tablespoons per bulb, because it lowers soil pH.
- Kelp meal; another natural fertilizer which is low in nitrogen and high in potassium, but also packed with trace minerals, so great for your allium bulbs health. If you have it, this would be my favorite “supplement”. Use 1 to 2 tablespoons per bulb.
- Comfrey mulch or comfrey tea; it is rich in potassium too; we usually dilute it (1:10) twice when we water after the flowers are spent and before the leaves die off.
Now you have fed them…
3. Improve Drainage and Soil Texture
Imagine being an allium bulb underground trying to fatten up, but the soil is too hard… Or, imagine if it is all wet around you when you are preparing to go to sleep…
In the first case, you would struggle to stretch and grow freely. In the second, you may catch disease – at the worst time of all!
So, this is the time to improve drainage and texture (especially if your land has clay or lime/chalk based soil). Scatter a 2-inch (5 cm) layer of coarse gardening sand around your allium bulbs (or gypsum if it is heavy clay), this will solve the two problems.
I actually suggest you do it before the flowers are spent, when your alliums are still in bloom; that will give the sand or gypsum more time to penetrate deep into the soil (allium bulbs go very deep underground!) But if you haven’t done it yet, do it now; you are still in time. And it will still keep them safe and dry later on.
4. Mulch
After you have improved the soil and laid the compost (and supplements, like bone meal etc.); it is time to mulch. Bulbs grow better with steady conditions, and this way, you will keep moisture and temperature steady, and you will protect the nutrients in the ground.
5. Remove the Leaves When they Have Dried Up
Some gardeners leave the foliage there, but I’d rather not – especially in humid climates. So, the leaves of your alliums will fade, then yellow and finally dry up. They can collect water and let it slide underground, ruining your big bulbs.
As soon as the leaves are dry, they are easy to pull off and you will not damage the bulb. Help yourself by holding the foliage clump at the base with one hand; this way, you won’t risk pulling or displacing the bulb.
6. Mark the Spots Where the Bulbs Are
Next, or even better while you remove the leaves, get some sticks, write “allium” on them and plant them in the ground.
Of course, you will want to grow other plants there, also bulbous perennials, so, you don’t want to risk ruining the big allium bulbs when doing so.
And this leads us into the next point…
7. Divide and Propagate Thick Bulb Clumps
As I said, it is partly true that one you plant alliums, you can leave them there without uprooting them every year. However, the big bulbs underground propagate; they grow little “babies” and that gives you very dense clumps.
Luckily, alliums are very slow, so you will only have to divide dense clumps every 4 to 8 years on average (sometimes even 10!) The good news is that you will get new plants for your garden for free.
“How do I know if I need to split up the clumps?” Look at how dense the foliage is; if it is too thick, it means that there are many bulbs crammed together underground. Also, dense clumps will produce smaller blooms (maybe more in number, but disappointing in size). How?
- Wait till all the foliage has yellowed or dried up, then use a fork, keep it about 6 inches (15 cm) from the leaves, lift the clump gently (you can do this from more sides).
- Then, clean excess soil, and gently divide the bulbs; each should keep its own roots.
- Replant them as soon as possible. There’s no need to dry them up or store them – alliums are very “easy-going” perennials.
Done!
8. Water Alliums Correctly after They Bloom
By now you must have understood that alliums’ worst enemy is excessive moisture… Now, while the leaves are green, just keep your usual watering routine – your flowering beauty is still awake and fully functional.
Keep the soil humid but never wet.
However, as soon as they start yellowing, reduce watering; your allium wants to dry up at this stage, the bulb has fattened as far as possible, and you need to help it in this process.
Later on, when the bulb is dormant, you absolutely need to avoid excessive watering, in fact…
9. Choose Suitable Plants to Grow where Your Allium Bulbs Are “Sleeping”
Now you will want your flower bed or border to have new flowering plants for summer and fall. But if you have allium bulbs, you cannot grow any variety. This follows from the point before: you need to keep the soil fairly dry.
So, avoid humid loving plants and choose drought tolerant varieties, or flowers that require little watering.
So, don’t grow cardinal flower (Lobelia cardinalis), swamp milkweed (Asclepias incarnata), Joe-Pye weed (Eutrochium purpureum), rose mallow (Hibiscus moscheutos) or blue vervain (Verbena hastata). Instead, choose varieties like lavender (Lavandula angustifolia), Russian sage (Salvia yangii), purple coneflower (Echinacea purpurea), blanket flower (Gaillardia aristata), Yarrow (Achillea millefolium), catmint (Nepeta × faassenii), butterfly weed (Asclepias tuberosa), stonecrop (Hylotelephium spectabile), globe thistle (Echinops ritro) or tickseed (Coreopsis verticillata).
10. Only if You Live in a Region with Very Wet Summers…
Alliums are cold hardy (to USDA zone 4 usually), so you don’t need to store them away in winter; in fact, you need to plant the bulbs in fall… But there is one exception: areas with very wet summers, and I am thinking Florida, Louisiana, Mississippi, Alabama, and Georgia.
In this case, I suggest you protect your allium bulbs during the summer months, or they may rot.
- Uproot them as we saw in section 7.
- Clean the bulbs thoroughly.
- Let them dry in a shaded and well-ventilated spot for at least 3 days, better for a week, spreading them in a single layer on a flat surface.
- You can also sprinkle them with sulfur powder; it will protect them from molds and fungi.
- Use a paper bag or mesh bag, and put them in with sawdust, peat moss or coco coir.
- Place them in a dry, cool and dark place, inspecting them regularly.
Replant them when fall starts (September to October).
Now we have seen what to do after your alliums bloom, let’s talk about what to avoid at all costs!
Mistake Nr 1. Cutting Alliums’ Leaves (too Early)
The biggest mistake you can make is to cut the leaves after they have bloomed. The bulbs are at their weakest at this stage; just imagine how much energy they had to spend to give you those massive globular inflorescences.
Also cutting them too early is a mistake; as I said, wait till they are at least all yellow, or better fully dry.
Mistake Nr 2. Don’t Tie up the Leaves!
This is a very common mistake. Many people tie up the leaves of alliums after they have flowered, because they “look unkempt”. To start with, they will still provide a green decorative presence for some time, but the main problem is that they need to photosynthesize as much as possible to fatten the bulb underground.
If you tie them up, you reduce the foliage surface exposed to the Sun, so, you also hamper their ability to produce sugars (carbohydrates) via photosynthesis to store in their bulbs for next year.
Mistake Nr. 3. Overwatering Alliums after They have Bloomed
Another mistake to avoid is to overwater Alliums after blooming.
You may think that plenty of will fatten the bulbs, and it could well do it. But you want them to be fairly dry (or balanced) and packed with nutrients. What is more, they risk catching molds, fungi and even rot!
As I said, keep the normal watering routine till the leaves yellow.
Treat Your Alliums Well After They bloom and You will Get Massive Flowers Next Year!
As you can see, taking care of alliums after they have blooms dis not hard nor laborious. Just follow these simple tips (and avoid mistakes) and you will get massive flowers next year, and the year after, and after…
