Bulb catalogues land in August, and they cause more confusion than any other page in the gardening year. Half of what is on offer has to go in the ground within the next ten weeks. The other half will rot if you plant it now and has to wait until next May. Both are sold side by side, often on the same spread, with nothing on the packet that makes the difference obvious.

The dividing line is not the plant. It is what winter does to it. Spring bulbs need a long cold spell underground before they will flower at all. Summer bulbs are killed by frozen soil and sit dry in a shed until the frosts are over. This comparison sets spring bulbs against summer bulbs the way the decision actually arrives in a European garden in autumn: what goes into the bed now, what comes out of it now, and what waits until spring.

Quick Comparison

Factor	Spring bulbs	Summer bulbs
Flowering season	March–June	June–October
Typical examples	Tulip, daffodil, crocus, hyacinth, allium, muscari	Dahlia, gladiolus, begonia, canna, lily
When to plant	September–November	April–May, once the frosts are past
Why then	Roots form while the soil is still warm	Soil has to be above roughly 10 °C
Cold requirement	12–16 weeks below about 9 °C, or no flowers	None, and hard frost kills most of them
Hardiness in the ground	Fully hardy	Mostly frost-tender
Planting depth	2–3× the bulb's own height, usually 10–20 cm	5–15 cm depending on type
Spacing	8–15 cm	12–15 cm for gladioli, 30–40 cm for dahlias
After flowering	Leave the foliage six weeks, then let it die back	Lift and store, or mulch heavily where winters are mild
Comes back on its own	Daffodils, crocus and alliums for years. Most tulips do not	Yes, if lifted and stored, or in mild winters
Sold as	Dry bulbs, autumn only	Tubers, corms and rhizomes, spring only
Main risk	Rot in waterlogged winter soil	Frost, in the bed or in storage
Cost per season of colour	Low, especially where they naturalise	Higher, but the cutting season is long

The Core Difference: One Needs Winter, the Other Cannot Survive It

Spring bulbs: winter is the instruction

Everything in the autumn catalogue comes from a climate with a real winter. Tulips are Central Asian steppe plants, daffodils and crocus come from Mediterranean hillsides and European woodland, and all of them survive a hostile season by packing next year into a bulb and going dormant.

That matters for one practical reason: the flower for next spring is already formed inside the bulb you are holding in August. It is not waiting for warmth or feeding. It is waiting for a long cold spell, roughly 12 to 16 weeks below about 9 °C, which is the signal that lets the stem extend when temperatures rise again. Plant a tulip in March and you skip that signal. You get leaves, a short stem and often no flower at all.

The same biology sets the deadline. Autumn-planted bulbs put out roots while the soil is still around 10–13 °C, and rooting more or less stops once the ground turns properly cold. A bulb pushed into November mud that never rooted is not dormant. It is simply sitting there, and on heavy soil it usually rots.

Summer bulbs: frost is fatal

Dahlias come from the highlands of Mexico, gladioli and crocosmia from southern Africa, begonias from the tropics. None of them evolved alongside frozen ground. They survive a dry season, not a cold one, which is why the storage organ is a tuber or a corm rather than a true bulb, and why a dahlia tuber in soil that freezes turns to mush.

So the calendar runs the other way. Summer bulbs go out after the last frost: mid-May in the Czech Republic, Slovakia and inland Germany, after the Ice Saints; late April on the Atlantic coast; earlier still around the Mediterranean. Many gardeners start them in pots under cover four to six weeks ahead to gain flowering time, then move them out when the risk has passed.

Lilies are the honest exception, and worth knowing before you argue with a catalogue. They are true bulbs, fully hardy, they flower in summer, and they can go in during either autumn or spring. Autumn planting usually gives the stronger first year.

What Goes In and What Comes Out This Autumn

The two groups swap places in the same bed within a few weeks of each other. In October you are often planting tulips a metre from the dahlias you are about to lift.

Climate	Plant spring bulbs	Dahlias and gladioli
Atlantic (Cfb)	Daffodils and crocus from mid-September, tulips from early November	On free-draining soil, cut back after the first frost and leave them in under 10–15 cm of mulch. Lift on wet clay, where rot does the damage frost does not
Continental (Dfb)	Mid-September to late October, before the soil drops below about 10 °C. Tulips last, late October	Lift about a week after frost blackens the foliage, dry them off, store frost-free at 5–10 °C
Mediterranean (Csa/Csb)	Late November into December, once the heat breaks. Tulips and hyacinths usually need eight to ten weeks of chilling in a fridge first	Leave them in the ground. Summer drought is the bigger threat than winter

If you are not sure which of these describes your garden, the European climate zones guide sets out where the boundaries fall.

The depth rule that covers every bulb

Plant at two to three times the bulb's own height, measured from the top of the bulb to the soil surface. A 5 cm tulip bulb therefore sits 10–15 cm down. Shallow planting is the single most common cause of floppy stems and bulbs that dwindle after one season, and in colder regions it is what leaves them exposed when the ground heaves in frost.

Planting: Where the Two Really Differ

Spring bulbs are about quantity and drainage. Point the tip upwards, and plant in groups rather than rows: seven to ten bulbs of one variety, placed a fist apart, reads as a drift, while the same bulbs spread thinly across a border reads as nothing. On heavy clay put a handful of coarse grit under each bulb, because standing water over winter kills far more bulbs than cold ever does. If you want tulips to last more than a season, plant them at the deep end of the range, 15–20 cm, where the bulb is less likely to split into small non-flowering offsets.

One more thing worth knowing before you spend money: voles and squirrels eat tulips and crocus, and leave daffodils, alliums and muscari alone, because those are toxic to them. On a plot with a vole problem, that is the cheapest decision you will make all autumn.

Summer bulbs are about space and support. Dahlias want 30–40 cm between plants and a stake driven in at planting time, not in August when the plant is already leaning. Gladioli go 10–15 cm deep and 12–15 cm apart, and planting them in small batches every fortnight from late April to mid-June gives you flowers for cutting into September instead of one short glut.

Neither group needs rich soil. Both need soil that drains. On a bed that has just carried a hungry crop, a light dressing of compost is plenty, and the work you did on structure in spring matters more here than any feed, as our guide to improving garden soil explains.

After Flowering: Six Weeks of Patience or a Box in the Shed

Spring bulbs build next year's flower in the six weeks after the last petal drops. That is what the untidy yellowing foliage is for. Mow it, tie it in knots or cut it off early and you get a smaller flower next spring, or none. Deadhead the spent blooms so the plant does not spend energy setting seed, then leave the leaves until they pull away easily.

Summer bulbs need the opposite kind of attention, and it lands in autumn. Where winters freeze, lift dahlias and gladioli after the first hard frost has blackened the top growth. Cut the stems back to about 10 cm, shake off the soil, let them dry for a fortnight somewhere airy, then pack them in dry compost or sand and keep them frost-free at 5–10 °C. Check the box once a month: a shrivelled tuber wants a light misting, a soft one comes out before it spoils the rest. Divide clumps in spring, when the growing points are visible.

What About Garlic and Onions?

They are autumn bulbs too, they go in the same October window, and they want the same free-draining soil, which is exactly why they end up competing for the same weekend and sometimes the same bed. Worth deciding in advance rather than in the rain: the autumn garlic planting guide covers timing and spacing, and setting up the autumn garden puts the whole month in order.

Who Should Plant Spring Bulbs?

Almost everyone, because nothing else gives as much colour for the money. A hundred crocus corms cost less than one shrub and flower in the gap between February and the first perennials, when the garden has nothing else to show. Choose spring bulbs if you want that early season, if you have a lawn or an area under deciduous trees where daffodils and crocus can naturalise and multiply on their own, or if you simply want to plant something once and stop thinking about it.

Treat tulips separately from the rest. Most large garden hybrids give two or three good seasons and then dwindle, so plan on replanting them or grow species tulips such as Tulipa tarda and Tulipa sylvestris, which are smaller, come back reliably and cope better with a wet European winter.

Who Should Plant Summer Bulbs?

Choose summer bulbs if you cut flowers. Dahlias flower from July to the first frost, which is the longest cutting season of anything you can plant, and the more you cut the more they produce. Gladioli, lilies and crocosmia extend the same idea through the middle of summer, when spring bulbs are long finished and perennials are between flushes.

The honest condition is the autumn job. If you garden on cold, wet clay in a continental winter and you know you will not get round to lifting and storing tubers in November, buy fewer dahlias and more alliums. If your winters are mild and the soil is free-draining, that job largely disappears and summer bulbs become as low-effort as anything else in the border.

The Verdict

Spring bulbs vs summer bulbs is not a contest, because they occupy the same ground at opposite ends of the year. The real difference is the deadline. Summer bulbs can be ordered in January and nothing is lost. Spring bulbs have a window that closes when the soil cools, and a bulb that misses it is a bulb wasted.

So the order of work for the next ten weeks is simple: get the spring bulbs into the ground first, deepest ones and daffodils in September, tulips once the weather turns in late October or November. Lift the dahlias when frost tells you to, and leave the summer order until the catalogues come round again. A bed planned that way carries crocus and daffodils in March, tulips and alliums in May, and dahlias from July to the first frost, from the same square metre of soil. Keeping track of what is buried where is exactly the sort of thing a garden plan is for.

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