Spring bulbs truly lift our spirits after a long winter. Their oh so cheery dispositions break the monotony of greens and browns and suddenly, we have colour! Yellows, blues, pinks, reds, purples! We transition from monochrome to technicolour. The wonderful thing about container displays is that you can shuffle pots around to keep the display looking its absolute best. When those early flowering crocus, iris, and early daffs are fading, swap them out for the musacri, richly coloured tulips, majestic crown imperials, and pom-pom alliums. With a little forethought in planning and planting, you can have a display in bloom from February right through to June.
Below, you'll find my best tips and advice for potting spring flowering bulbs in containers: Planting depths, potting mixes, crocks, winter protection, plus watering and feeding. There is a wealth of information out there about how you plant bulbs in pots, planters, or any container you wish. Sadly, most of it is over complicated and unnecessarily convoluted and it needn't be. Potting up bulbs is very simple. It is easy gardening! Essentially, you need a container that drains well, gritty potting compost that also drains well, and one general rule for planting depths. That's it. All the rest is nuance.
What do I mean by drains well? Answer: Water needs to be able to pass freely through the compost and out the base of the container. Waterlogged compost is an absolute No!No! Waterlogging leads to rotting and flowering will be poor if the bulbs survives at all. Unfortunately, in waterlogged soils, almost all bulbs will rot and die before ever seeing the light of day and that's the single most important tip you need to know.
Bulb planting depths
A quick online search will show you a range of very elaborate depth gauges and graphics showing the precise depth of each individual species of autumn planted bulbs. But here's the thing... they make it so incredibly complicated! And, again, it shouldn't be! I follow a general guiding rule that bulbs are planted at a depth roughly 3x their own height as a minimum. So, if a bulb is 4cm (roughly 1½in), you plant it 12cm deep (about 5 inches). Don't make it complicated. For temporary planting in pots, the planting depth is arbitrary, so put the ruler away! You need a decent amount of compost below for the roots (say 15cm or 6in), and half as much above.
Interestingly, if bulbs weren't already remarkable enough, many bulbs actually have 'smart' roots. Yes! You did read that right. Many flowering bulbs have 'contractile' roots and are able to adjust their depth, if they find themselves planted too shallow... The wonder of bulbs continues!
"A recent study published in the Journal of the American Society for Horticultural Science proved that bulbs can adjust their planting position by moving deeper into the ground, apparently in search of moister, more conducive growing conditions." (American Society for Horticultural Science. "'Smart' Flower Bulbs Pull Themselves To Deeper Ground." ScienceDaily, 10 December 2007 - Read full here)
If you really do prefer to geek out and like nothing better than measuring bulb depths to the exact millimetre, here's a list of common bulbs and depths. Notice how many actually say 'three times their depth'.
- Snowdrops: 10cm or three times their depth
- Crocus: 10cm or three times their depth
- Daffodils: 15cm or three times their depth
- Hyacinths: 10cm or twice their depth
- Tulips: 20cm or three times their depth
- Fritillaria imperialis, crown imperials: 30cm or three times their depth
- Fritillaria meleagris, snake's head fritillary: 10cm or five times their depth
- Globe alliums: 30cm or three times their depth
- Allium sphaerocephalon: 15cm or three times their depth
- Camassia: 10-15cm deep, or around twice the height of the bulb
"Which compost have you achieved best results with?"
Having sampled a few over the years, the brand I return to time and again is the SylvaGrow bark-based peat-free multipurpose compost. Mix this with 25% grit for added drainage and you should be off to a flier. Throw in a handful of Fish-Blood-Bonemeal slow-release for a little extra fertility, given that practically all bagged compost only has enough feed for 6-8 weeks and many bulbs are in growth for months.
A question from Instagram by @lilac_tree_house
Bulb compost (potting) mix
My bulb potting compost is a blend of SylvaGrow peat-free multi-purpose compost, sieved garden compost, and sieved leaf mould. The final ingredient is horticultural grit for increasing drainage. I make this up in batches, in a wheelbarrow. It’s not scientific and probably overly alkaline (shock, horror!) But it seems to work very well! The rough measurements are 50-30-10-10 which translates to:
Half bag of SylvaGrow peat-free multipurpose compost
One bucket of garden compost
Half bucket of leafmould
Half bucket of horticultural grit
Three standard scoops (70g) of Fish-Blood-Bonemeal (NPK 3-9-3)
I mostly eyeball my compost mix as garden compost and leafmould varies in consistency from year to year, season to season. Rubbing it through my fingers, I know when the overall blend is right. It shouldn’t stick together when you squeeze it in your hand. It should be very open and crumbly. You just get a feel for these things.
Remember, you need water to moisten the compost but pass through without waterlogging. Roots source the water and nutrition to fuel the leaves, leaves power the growth and development of the bulb. If you want to grow the bulb and pack it full of nutrients for the following season, its best to give bulbs quality compost and a little extra fertility - either Fish-Blood-Bonemeal or liquid seaweed feed. If you’re growing bulbs as annuals, you don’t really need to be overly concerned with nutrition.
Some of our large planters have over 100ltr capacity, that’s more than 26 US gallons, taking more than two full bags of compost alone. We get through so much compost, I should buy shares in SylvaGrow! Those 40ltr bags of compost (now £9 per bag), making the garden compost ever more valuable and thankfully I can make over 3m³ here in the garden. That makes a big difference to the wallet!
NOTE: Perlite is a useful ingredient to maintain good drainage in a potting mix. It’s an extremely light alternative to grit. Unfortunately, it has questionable sustainability credentials. as it’s essentially an expanded volcanic mineral, heated to 1000°C until it ‘pops’. This uses considerable amounts of energy. I’m not going to preach, but I have stopped using both perlite and vermiculate, switching to horticultural grit (crushed granite) and composted bark.
To crock or not to crock, that's the question!
Previously, I’ve always advised using crocks - broken bits of pots or tile placed in the base of the pot to aid drainage and to stop the compost washing out the bottom. However, recent research by Which? Magazine has debunked this practice as pure dogma passed down by generations of gardeners. A layer of grit or sand is said to work much better and thankfully I have often recommend that too. Gravel and shingle are never far away in my garden and I simply grab a couple of handfuls to line the base of the pot. In theory, if your compost is gritty and free draining and your pot has plenty of drainage holes, waterlogging should not be an issue anyway.
Looking for more information on bulbs? How they grow? Are tulips perennial?
The bulb panting method
Add a crock or layer of grit/gravel into the base as a drainage layer. Part fill your pot with roughly 15cm (6 inches) of compost, giving plenty of room for roots and lots of nourishment for the bulbs. Place a layer of bulbs on the compost, pointy end upwards, the hairy tuft of roots facing down. Top up with compost leaving a 2-3cm gap below the rim. Label. Done. Easy. But read on for the finer methods and a little more knowledge...
Bulbs planted in the ground have access to the threadlike 'wood wide web' of mycorrhizal fungi and the soil biome. Bulbs in pots however are usually planted in sterile compost from a bag, which is one reason I add garden compost and leaf mould. I know many home gardeners won’t have access to homemade compost but you can add mycorrhizal fungi to pots using Empathy’s Bulb Starter or mycorrizal RootGrow. Just sprinkle a handful on the compost before placing your bulbs.
Ready to plant your bulbs?
Once, you've added your drainage layer, pour in the compost and firm down. Sprinkle over the Bulb Starter or mycorrhizal fungi granules. Place the bulbs in the pot, pushing them firmly into the compost and mycorrhizal. I find concentric circles work nicely and they’re easy. No need for advanced mathematics here. I space-out bulbs just one finger-width apart. It will look too close, but trust me, it is very effective and with so many bulbs in one pot you get a really punchy show of blooms. For example, with a standard bucket-sized pot, I find 12-15 tulip bulbs will produce a great show. Just make sure the bulbs are not actually touching.
Now cover the bulbs with more compost, pushing the compost gently in between the bulbs, so there are no voids or gaps that might fill with water and rot the bulbs. Be gentle so you don’t overturn the bulbs, although their shoots are quite adept at finding their way to the surface. Make sure there is a gap of roughly 2-3cm (1 in) at the top, below the pot rim, so you can water easily without spilling over the top.
Although not essential, a topping of grit is very useful. In the spring, weed seeds find it difficult to germinate and any that do are very easy to pluck out. When watering, the grit stops the compost sloshing about and making a mess. Just aesthetically, the fresh green stems and spring blooms look great set off against the grit. We’re gardeners. It’s ok to be fussy and make things pretty! Grit can also deter small rodents (mice and voles) however, burying a section chicken wire is far more reliable against tenacious rats and squirrels. Don’t worry, bulb shoots are very tough and will work their way through the gaps in the wire without any issue.
Finally, label the pot! This is important! You'll know what to expect in the new year and, crucially, keep a note on which cultivars worked for you, so you can order more next season. With so many colours and forms available (especially for narcissus and tulips) it great to have a mainstay or regulars while leaving room to try a few new cultivars each season.
If the pots are to go under cover for winter, water them first. Give those bulbs and compost a good soaking and let them drain. They probably won't be watered again until the spring. Make sure you can see water flowing out of the base so you know the drainage is working. If the pots are to stand outside in the elements, you can still water the pots, but just enough to settle the compost. The winter rains will do the rest.
Setting up
Table, tools, trugs, compost, pots, and bulbs all ready for a mammoth bulb-planting session
Compost Mix
Half bag of peat-free multipurpose
One bucket of garden compost
Half bucket of leafmould
Half bucket of horticultural grit
Fish-Blood-Bonemeal (NPK 3-9-3)
Planting bulbs
Arranging tulip bulbs in concentric circles with just a finger's width between each bulb.
Grit topping
Deters small rodent, prevents weeds taking hold, stops compost slushing about when watering, looks good and tidy.
How to protect your bulbs over winter?
If your winters are mild, like here in the South of England where we rarely see temperatures fall below -5℃ (23℉), you can leave your potted bulbs outside all winter. However, you might want to consider tucking them against your house because of the incessant rain! In the UK, the vast majority of winter rains blow in from the south west, so tucking those pots up against the north or east side of your house, keeps them out of the worst of any winter deluge.
Bulbs are very hardy, so no need to worry about frost, snow, or ice. They absolutely detest waterlogged soils/compost. Even when the Beast from the East locked the entire country in ice for weeks on end (temperatures down to -18℃ (0℉), potted bulbs in my garden were fine, because the free draining compost wasn’t waterlogged. It's the combination of waterlogged soils that freeze solid that kills your bulbs.
During the winter, my pots all sit on gravel so they can drain freely. It’s a very good idea to invest in pot feet, or make small chocks from wood, if your pots sit on flat patio slabs. Those pots must be able to drain. I cannot emphasise this enough!
If you have problems with rodents eating your prized bulbs, lay sections of chicken wire or metal wire fencing over the pots and weigh these down with bricks. Do not cover the pots with anything solid as this will reduce airflow and promote mould and fungal growth. You'll also be creating a cosy environment for slugs that will happily feast on any shallow-planted bulbs.
When you see fresh shoots nosing through, you can remove the metal guards. Here, in my garden, the rodents seem far less interested when the bulbs are actively growing. Move the pots out to their final position as those bulbs will now need sunlight. As you're moving them, you can also check moisture levels. If they’re really light, the compost has dried out, so give them a thorough soaking. If they feel heavy, leave them and just double check they can drain.
"How often do you water your bulbs in containers?"
It really depends on the size of the containers and how well drained they are. As a rule, I water our containers weekly giving them a thorough drenching, so water is draining out the bottom. This seems sufficient to keep them happy. If we get one of those baking springs, then I up the watering to twice weekly and use the tips below to gauge how much moisture is in the compost.
A question from Instagram by @stefanomnd
Watering & Feeding
It’s difficult to recommend a general watering rule, now that our springs are so changeable. One year we have a borderline drought, the next it floods. Once in growth, keep checking the compost by lifting the pot or pushing a finger in as deep as you can and seeing if there is still moisture there. Remember, most peat-free looks dry on top but retains moisture below. I water our containers weekly. Giving them a through drenching so water is draining out the bottom. This seems sufficient, unless we get one of those baking springs, then I up the watering to twice, weekly. Most bulbs will tell you they're thirsty by drooping. The flower stems will droop and the leaves buckle and crinkle. Learn more valuable watering tips here.
Many gardeners swear by feeding their bulbs liquid seaweed feed all season, as soon as they’re in leaf. I’m not against this, but I’m not entirely convinced either. I really need to do a trial of my own and see whether this actually makes any difference to an organ that stores its energy and nutrients before shutting down and going dormant all summer. Where I can see feeding would be of benefit is just as the flowers fade and the bulb is still in full leaf, i.e. the Recharge Cycle also known as Regeneration. Rather than feeding all season long, because seaweed feed is not exactly cheap, let’s use it where it’s most effective. During the bulb’s recharge cycle, it’s packing in more nutrients and growing the bulb, ready for dormancy and life again next season.
"What about layering plants in planters?"
In essence, the increasingly popular 'Bulb Lasagne' is basically multiple layers of bulbs, all planted in the same pot, one layer planted over another. Generally, the larger later flowering bulbs like tulips and alliums are planted at the bottom. The early-flowering small bulbs like crocus or reticulate iris on the top.
Questions from Instagram by @juliehoolie6 & @mrsbadores
Anyone for Lasagne?
Bulb lasagnes are especially useful if you’re limited on space and/or the number of pots. In effect, you're increasing the flower power of each pot, either by dramatically increasing the number of blooms, the variety, or lengthening the season. The easiest lasagne 'recipe' is just two layers, with two distinctly different bulbs, with entirely different flowering seasons. Here’s one example: Plant tulips in the pot first as your bottom layer, cover with compost, then place early flowering reticulate iris on top, then backfill. By the time these dwarf iris have faded, the tulips are powering through. Iris leaves are also very slender and won't interfere with the tulips.
You can also experiment with bulbs flowering at exactly the same time for delightful spring combinations, such as muscari with either narcissus or tulips, or an early combo of crocus and iris reticulata. Yet another alternative is to plant two layers of tulips to include both early and late flowering cultivars, so there is succession and a lengthening of the flowering season.
In theory, you could plant alliums in the bottom, then tulips, then narcissus, then crocus, and even snowdrops on top of that. It would need to be a pot of considerable depth! However, the more bulb layers you have, the more leaves they’ll be. Spring bulb leaves persist for weeks as this is how they recharge their bulbs each season. It's not such an issue with the narrow slender leaves of crocus and iris, but tulips, narcissus, and alliums all have substantial leaves. causing real congestion. With all those lush leaves packed in, subsequent damage from slugs and snails may be more of an issue. They'll also be thirsty with so much root competition, so you'll need to increase the watering frequency.
The lasagne is very easy to get wrong and you can find yourself with a pot full of leaves and precious little flowering, so be aware. It takes a little planning and careful spacing - so the bulbs are wider apart to allow for growth from below to push through. Start with the basics: Just two layers, an early and late flowering combo. See how you like the effect. The following year experiment with bulbs that flower simultaneously. I would suggest you still keep those 'simple' pots of bulbs going before diving head first into your lasagnes. Just know that although they're fashionable and seem really clever, it's ok not to like Lasagnes. It's ok to be old fashioned, like me. (Honestly, I'm not a fan!)
More tips...
- Decide on a planting scheme before you buy your bulbs. Are you going to have pots of mixed colours and mixed bulbs? Or one colour/type per pot? Complex vs Simple planting styles. My approach is very much on the simple side. One container, packed with one variety of bulb. No lasagne. No multi-bulb sandwiches. No faffing. Just one layer of bulbs. Colour schemes change from year to year, whether it's cool and elegant with whites, pastel pinks, and purples, or spicier with oranges, hot pinks, and bold yellows. The White Garden style is always timelessly elegant!
- Consider the eventual plant size versus pot size. It would look rather odd having a huge imperial crown fritillary in a tidily pot! As well as the overall size of the plant, bulbs need space below to send down roots and fuel their development. In small pots (half a bucket or 3-4lts for example) I plant, crocus, reticulate iris, muscari, and dwarf narcissus. The larger narcissus, tulips, alliums, and imperial fritillary all go in bucket-sized pots and planters as a minimum. (I’ve never planted camassia in pots, they’ve always been planted into the borders)
- Drainage is absolutely key. The fear is always that bulbs rot away in waterlogged compost, without ever seeing the light of day. I really like vintage galvanised or copper planters as I can drill extra drainage holes. The buckets are especially useful as they're so easy to move about thanks to the bail (handle). Ceramics and most terracotta pots are limited to just one hole and its difficult to drill new holes through either material without breakages. Besides, I find ceramics particularly heavy and awkward to move. If you have mobility issues, consider plastic pots or metal buckets with handles.
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