A bag of bulbs is not one question. Spring-flowering bulbs are planted in autumn and need soil that has cooled below 60°F, summer-flowering bulbs go in after the last frost once soil is back above 55°F, and the autumn-flowering kinds go in during late summer. Work out which group you have and the timing stops being a guess.
There are three planting windows in a bulb year, and which one you are in is decided by when the bulb flowers rather than by the month.
Flowers this autumn
Flowers the following spring
Flowers this summer
Read across a row to see the two things that matter: the months the bulb is planted, and the months it flowers. They are rarely in the same season.
Depth and spacing figures are for well-drained soil. On heavy clay, set bulbs an inch or two higher than the chart says.
| Bulb | Flowers | Planted | Trigger | Depth | Spacing |
|---|---|---|---|---|---|
| TulipsIn zones 8 and warmer the bulbs need refrigerator chilling before they go out. | Mid to late spring | Autumn | Soil below 60°F | 6 to 7 in. | 4 to 6 in. |
| Daffodils | Late winter into spring | Autumn | Soil below 60°F | 6 to 7 in. | 4 to 6 in. |
| CrocusNaturalizes in lawn edges, but the foliage still has to die back before mowing. | Late winter into early spring | Autumn | Soil below 60°F | 2 to 3 in. | 3 to 4 in., in groups |
| HyacinthsRarely worth dividing, so treat a hyacinth planting as a short run rather than a permanent one. | Spring | Autumn | Soil below 60°F | 4 to 6 in. | 6 in. |
| Alliums | Late spring into early summer | Autumn | Soil below 60°F | 3 in. | 12 in. |
| Grape hyacinths | Spring | Autumn | Soil below 60°F | 2 to 3 in. | 4 in. |
| Squill and snowdropsSmall bulbs read better scattered and planted where they land than lined up in rows. | Late winter into early spring | Autumn | Soil below 60°F | 2 to 4 in. | 3 to 6 in. |
| Autumn crocusFlowers arrive on bare stems weeks later, before any leaves appear. | This autumn | Late summer | Warm soil, planted on arrival | 3 in. | 12 in. |
| DahliasTender: lift and store the tubers before the first autumn frost. | Midsummer until frost | Spring | Soil above 55°F, after frost | 6 in. | 2 to 4 ft, by cultivar |
| GladiolusSet a second batch in two weeks later if you want flowers over a longer stretch. | Summer | Spring | Soil above 55°F, after frost | 3 to 6 in. | 2 to 4 in. in the row |
| Cannas | Summer until frost | Spring | Soil above 55°F, after frost | 1 to 2 in. | 12 to 24 in. |
| LiliesHardy lilies are the exception: they can be planted in either window, and many growers prefer late autumn. | Early to late summer | Spring, or late autumn | Soil above 55°F, or plant in late autumn | 4 to 6 in. of soil over the bulb | 6 to 10 in. |
| Tuberous begonias and caladiumsBoth want part shade, and neither survives a frost. | Summer | Spring | Soil above 55°F, after frost | Barely covered | 12 in. |
Bulbs are not one group of plants, and the word covers more than true bulbs: crocus and gladiolus grow from corms, dahlias from tuberous roots, cannas from rhizomes. What they share is an underground store of food and a dormant season, and what separates them is when they flower.
A bulb that flowers in spring needs its cold period first, so it goes into the ground in autumn and sits there dormant through winter. A bulb that flowers in summer has no cold requirement at all and cannot take a frozen winter, so it is planted in spring and lifted again in autumn. A third, smaller group flowers in autumn itself and is planted in late summer.
That is why a single date cannot answer the question, and why the same species still moves by several weeks from one garden to the next. Autumn arrives later in a warm coastal garden than it does inland at the same latitude, and the ground freezes at very different times.
The cleanest signal for autumn planting is soil temperature, and extension guidance puts the trigger below 60°F with around 55°F as the target. That range is what root growth needs: warm soil encourages rot and premature top growth, and soil that is already freezing stops the process before roots can form.
If you would rather work from the calendar, the usual shorthand is 6 to 8 weeks before the ground typically freezes in your area. The two rules tend to point at the same fortnight, but soil temperature absorbs an unusual autumn better than a date does. September and October are the months that usually leave enough rooting weather before the freeze.
The forgiving edge of the window is the late one. Bulbs can still go in until the ground freezes, and plenty of gardeners plant well into November. What you are giving up is rooting time, not the planting itself.
The spring window runs the same rule backwards. Summer-flowering bulbs want soil that has reached at least 55°F and frost that has passed, and bulbs planted into colder soil than that tend to rot before they sprout.
Spring-flowering bulbs need a long cold stretch to flower well, on the order of 12 to 16 weeks, and a mild winter may not deliver it. In zones 8 and warmer the practical answer is to chill the bulbs yourself: keep them at around 38 to 45°F for 6 to 12 weeks, then plant them out at the coolest point of the season.
Keep bulbs away from ripening fruit while they chill. Fruit gives off ethylene gas, and it can damage the flower that is already formed inside the bulb. A refrigerator used for fruit is not a good chilling space for that reason.
The same logic explains why a warm-climate garden can still plant tulips and daffodils successfully while never giving them the winter they expect. The cold requirement does not disappear; it just moves indoors.
Two depth shortcuts get published and they do not quite agree, because one measures the bulb's height and the other its width. One widely used version is four times the height of the bulb from soil surface to tip; another is two and a half to three times the bulb's diameter. Treat either as a starting range rather than a number, and let the species chart decide, because a crocus and a daffodil are not in the same league.
Set the bulb with the growing tip up and the root plate down. In most bulbs the pointed end is the tip and the flat, slightly dished end is where the roots come from. If you genuinely cannot tell, planting a bulb on its side is usually survivable; planting it upside down is not.
Drainage matters more than richness. Bulbs sit in the ground through the wettest part of the year and rot in soil that stays saturated, so prepare the bed deeply and avoid compacting the soil directly beneath the bulbs, which creates a hard layer that holds water.
One site note worth taking seriously: a south-facing bed right against a foundation warms early and can push growth out ahead of the last freeze, which then damages it. Slightly cooler ground that stays closed a little longer is the safer choice.
Once the ground has frozen, mulch the bed with a few inches of loose material. The point is not warmth but consistency: it stops the repeated freezing and thawing that breaks roots and pushes bulbs out of the ground. Pull the mulch back in early spring before growth gets going, or leave it if the shoots can come through it easily.
The single most important thing you can do after the flowers fade is leave the foliage alone. Those leaves are feeding the bulb that will flower next year, and cutting them while they are still green takes that away. Let them yellow and die back on their own, then clear them. Deadheading matters for the same reason: a seed head is food being spent somewhere you do not want it.
Feed, if you feed at all, while the foliage is still green. The flower inside the bulb is already formed when you plant it, so feeding then is working on next year's bulb.
Bulbs left in place for several years eventually crowd and lose vigor. When blooms start coming in smaller, lift them after the foliage has died back, separate the good bulbs, and replant them somewhere new.
The month is only a proxy. Work out which window your bulb belongs to, then let soil temperature tell you whether that window has opened.
Spring bloomers: plant in autumn, soil below 60°F.
Summer bloomers: plant after the last frost, soil above 55°F.
Autumn bloomers: plant on arrival in late summer.
The planting calendar reads your local soil temperature and the week ahead, then shows whether the autumn bulb window has opened or the ground is still too warm.
Bulbs are forgiving more often than they are ruined. Here is what each mistake actually costs, and what to do next.
The guidance here draws on the references listed below.
These are the questions that usually come up once the guide turns into real garden work.
That changes with the season. In autumn you are in the window for spring-flowering bulbs such as tulips, daffodils, crocus and hyacinths. In spring, once frost has passed and soil is above 55°F, it is the turn of dahlias, gladiolus, cannas and lilies. In late summer, autumn crocus and saffron crocus go in straight away.
For spring-flowering bulbs, late September into October is the usual target, because it leaves the most rooting weather before the ground freezes. For summer-flowering bulbs, the equivalent answer is mid-spring, after the last frost and once soil has passed 55°F.
If they are spring-flowering bulbs, they will not have had the cold period they need, so expect leaves and few or no flowers, and small ones at that. They are usually fine left in the ground and will flower properly the next spring.
If you mean summer-flowering bulbs, yes, as long as they go in after the last frost and into soil above 55°F. Dahlias and gladiolus planted in early summer simply flower later, and gladiolus can be set in batches a week or two apart for a longer run. For spring-flowering bulbs it is the wrong end of the year: the soil is at its warmest and there is no rooting season left before they are due to flower.
Autumn-planted bulbs keep well for weeks if they stay cool and dry, around 60 to 65°F, with air moving around them instead of packed in a sealed bag. Check them for mold and discard any that have gone soft. Autumn crocus is the exception: it flowers within weeks of planting, so plant it on arrival.
The flower is already formed inside the bulb when you plant it, so fertilizer at planting goes toward next year's bulb. If you use it, phosphorus is the one worth placing at planting depth, because it barely moves through the soil and roots will not find it later if it is left on the surface.
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If this guide opened a next question, these are the guides to read next.
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