Summer bulbs: which ones to plant in spring according to your soil
Sommaire
- Why plant summer bulbs in spring
- Summer bulbs: the picture by variety, from dahlia to nerine
- How to plant summer bulbs in 7 steps
- Which summer bulbs for your soil: dry, cool, moist or partial shade
- When to plant summer bulbs?
- Perennial summer bulbs that stay in the ground
- Lifting and overwintering tender summer bulbs
- Summer bulbs in pots: the right guidelines
- Summer bulbs throughout the seasons
- Mistakes to avoid with summer bulbs
- Our summer bulbs and their fact sheets
- Summer bulbs and autumn bulbs: do not confuse them
- Our tips for successful summer bulbs
🌱 When: From March to May, for those who are sensitive to the cold after the last frosts: gladioli from mid-April to May, dahlias in the ground from mid to late April (RHS)
☀️ Dry and warm soil: Gladiolus, lisianthus, crocosmia, agapanthus, nerine, freesia: they all need well-drained soil
💧 Cool or moist soil: Arum (Zantedeschia aethiopica), canna and dahlia, which like cool but well-drained soil
🌳 Partial shade: Tuberous begonia; crocosmia in light shade, sometimes with reduced flowering (RHS)
❄️ Hardiness (RHS): Lilium regale H6, crocosmia 'Lucifer' and Nerine bowdenii H5, arum H4, canna and African agapanthus H3; dahlia and begonia are not hardy
📦 Winter: Dahlias, begonias, hybrid gladioli, cannas and African agapanthus in cold regions: dug up or brought indoors before the first frost
Summer bulbs are bulbs, corms, tubers, and rhizomes that are planted in spring, from March to May, for flowers from June through the first frosts: dahlias, gladioli, cannas, lilies, crocosmias, agapanthus, tuberous begonias, freesias, arums, and nerines.
This guide classifies each genus by soil (dry, fresh, moist, partial shade) and by RHS hardiness, then tells you which to leave in the ground and which to dig up in autumn.
For the rest of the spring garden, see our guide what to plant in spring; our bulbs to plant in spring are gathered in a collection.
🌟 Why plant summer bulbs in spring
Summer bulbs are planted in spring because most come from warm regions and cannot withstand a cold, wet winter in the ground: planting them after the hard frosts prevents them from rotting before they even get started.
According to the RHS bulb planting guide, tender summer bulbs, including gladioli, are planted in early spring, while hardy summer bulbs such as lilies and crocosmias can also be planted in September and October.
The same page gives the basic rule: plant most bulbs at two to three times their own height, or 10 to 15 cm for a 5 cm bulb.
| Benefit | What it means |
|---|---|
| Flowers from June through the frosts | Dahlias flower from summer through the first frosts, nerines in autumn (RHS) |
| Frost-free planting | March to May: the soil warms, tender bulbs get started without rotting |
| A genus for every soil | Well-drained for gladioli and lilies, fresh for dahlias, moist for arums, partial shade for tuberous begonias |
| Cut flowers | Gladioli, dahlias, freesias, and ranunculus make beautiful bouquets |
| Trade-off | Several genera are not hardy: they must be dug up or protected in winter |
📊 Summer bulbs: the genus chart, from dahlia to nerine
To choose your summer bulbs, first look at the hardiness of each genus, as this determines whether it will remain in the ground or need to be dug up in autumn. Periods, depths, and codes come from RHS guides and fact sheets, unless otherwise stated.
On the RHS (Royal Horticultural Society) hardiness scale, H3 corresponds to -5 to 1 °C, H4 to -10 to -5 °C, H5 to -15 to -10 °C, and H6 to -20 to -15 °C, at minimum temperatures.
| Genus | When to plant | Depth | Hardiness (RHS) | In winter |
|---|---|---|---|---|
| Dahlia | Tubers in the ground from mid to late April; plants started under cover in late May (the RHS dahlia guide) | Top of the tuber just below the surface, 60 cm between plants | Not hardy | Dig up by late November at the latest, or use 15 cm of mulch in mild regions |
| Gladiolus (Gladiolus) | Hybrids from mid-April to May; nanus from late March to mid-April (the RHS gladiolus guide) | 10 to 15 cm, spaced the same | Hybrids to protect; Gladiolus italicus H3; G. communis subsp. byzantinus left in the ground | Hybrids dug up in late summer or early autumn, kept dry out of frost |
| Canna (Canna × generalis) | March and April in pots at 10-16 °C, outdoors in late May (the RHS canna guide) | 10 cm, 75 cm apart | H3 | Rhizomes dug up in cold regions; 15 cm of mulch in mild climates |
| Lilies (Lilium) | Ideally in early autumn, or in spring (the RHS lily guide) | 1 times the height of the bulb; 2.5 times for lilies with roots on the stem | Lilium regale H6 | In place: most are hardy |
| Crocosmia | Corms in spring (the RHS crocosmia guide) | About 3 times their height, 10 to 20 cm apart | Crocosmia 'Lucifer' H5 | In place, under thick compost in cold regions |
| Agapanthus (Agapanthus) | Late March and April (the RHS agapanthus guide) | Neck of the plant under 5 cm of soil; pot at least 20 to 23 cm wide | Agapanthus africanus H3, evergreen; deciduous ones are hardier | A. africanus in a pot, brought indoors out of frost in cold regions; deciduous ones under fleece from November to early April, 15 to 23 cm of mulch |
| Tuberous begonia (Begonia) | Start in March or April at 18 °C, outdoors after frosts (the RHS outdoor begonia guide) | Hollow towards the top, barely covered | Not hardy (tender) | Dug up before the first frosts, kept out of frost, ideally at 7 °C |
| Freesia | April for prepared corms (the RHS freesia guide) | 5 cm | Can only withstand a few degrees of frost | Corms dried and stored in a warm place |
| Arum (Zantedeschia aethiopica) | In spring, after frost (the RHS arum and calla guide) | Rhizome barely buried | Z. aethiopica H4; colored callas under 5 °C | Arum in place under mulch; colored callas brought indoors |
| Nerine (Nerine bowdenii) | Dry bulbs in late summer (the RHS nerine guide) | Neck of the bulb above ground, 10 cm apart | H5 | In place, with no special care |
| Ranunculus (Ranunculus asiaticus) | Spring when the soil warms, see our fact sheet | Claws facing down, under 5 cm of soil (RHS) | Tolerates up to 0 °C once established (RHS) | Grown as an annual, replaced every year (RHS); see our fact sheet |
📋 Quick fact sheet
Common guidelines for all summer bulbs, according to the RHS and Météo-France.
| Guideline | The rule |
|---|---|
| Planting period | From March to May, the tender ones after the last frosts |
| Depth | 2 to 3 times the height of the bulb, except for exceptions (dahlia, nerine, begonia) |
| Spacing | At least 2 times the width of the bulb in the ground (RHS) |
| Soil | Well-drained for most; fresh for dahlia, canna, and arum |
| Exposure | Full sun for most; partial shade for tuberous begonia |
| Watering | Generously at planting, then by feel when the soil is dry to a depth of 2 to 3 cm |
| Late frosts | Frost recorded between May 14 and June 30 in at least one of the 130 plain stations for 49 out of 73 years, or 67% of the time (Météo-France) |
| Winter | Hardy in place; tender ones dug up and kept out of frost |
| In a pot | 3 times the height of the bulb, one bulb's width between each (RHS) |
How to plant summer bulbs in 7 steps
To successfully plant your summer bulbs, plant them in warmed, well-drained soil, at the right depth, point facing up, then water thoroughly once and wait for them to sprout.
| Step | The right action |
|---|---|
| 1. Sort the bulbs | Discard those that are soft or show signs of rot (RHS) |
| 2. Wait for the right time | Soil thawed and warmed; tender ones after the last frosts in your region |
| 3. Prepare the soil | Loosen and improve sandy or heavy soil with compost (RHS) |
| 4. Dig to the right depth | 2 to 3 times the height of the bulb, or 10 to 15 cm for a 5 cm bulb (RHS) |
| 5. Place point facing up | Groups of 5 to 10 for effect, spaced at least 2 bulb widths apart |
| 6. Backfill without tamping | Avoid treading on the soil above the bulbs (RHS) |
| 7. Water then wait | Water thoroughly, then check by feel; place a stake at planting for tall dahlias |
🧭 Which summer bulbs for your soil: dry, fresh, moist, or partial shade
The right summer bulb depends first on your soil: most want well-drained, warm soil, a few accept freshness, moisture, or partial shade. Here is the selection by situation, genus by genus, according to the RHS and NC State Extension.
| Your situation | The summer bulbs to choose |
|---|---|
| Dry, light, and warm soil | Gladioli, lilies, crocosmias, agapanthus, nerines, and freesias, all in well-drained soil; to complete, see our guide to the dry garden and our sun-loving plants |
| Fresh, rich but well-drained soil | Dahlias, which want fertile, fresh but well-drained soil (RHS), and cannas in a fresh border |
| Moist soil or pond edge | Arum (Zantedeschia aethiopica), accepted on the bank and even in shallow water, at most 30 cm deep (RHS); the canna tolerates a little standing water once established according to NC State Extension |
| Partial shade | Tuberous begonias, in sun or partial shade (RHS), and crocosmias in light shade, with sometimes reduced flowering (RHS); complete with our perennials for shade |
| Heavy and clay soil | Avoid lilies in the ground: they do not grow well in heavy or poorly drained clay (RHS); prefer a pot |
| Pot, balcony, or patio | Agapanthus, tuberous begonias, freesias, cannas in pots at least 30 cm wide (RHS); see our plants for balcony and patio |
| Cold region | Royal lily (H6), crocosmia 'Lucifer', and nerine (H5) in place; African agapanthus (H3) in a pot, brought indoors out of frost; dahlias, begonias, and hybrid gladioli dug up in autumn |
| Garden with a cat | According to the ASPCA (American Society for the Prevention of Cruelty to Animals), lilies (Lilium species) are Toxic to Cats (Cats: kidney failure); the ASPCA Begonia fact sheet classifies Begonia spp. as Toxic to Dogs, Toxic to Cats, Toxic to Horses, as well as Gladiolus species; Zantedeschia aethiopica is Toxic to Dogs, Toxic to Cats. Check every other plant before planting it |
🔑 When to plant summer bulbs?
Plant summer bulbs from March to May, starting with the hardiest and keeping the tender ones for the end, after the last frosts in your region: agapanthus in late March and April, gladioli from mid-April to May, dahlias in the ground from mid to late April, cannas and begonias started under cover then taken out in late May.
Beware of the Frost Saints, from May 11 to 13: Météo-France recorded frost between May 14 and June 30 in at least one of its 130 plain stations for 49 out of 73 years, or 67% of the time.
The general rules of planting are detailed in our guide when and how to plant bulbs.
💡 Hardy summer bulbs that remain in the ground
Hardy summer bulbs that can remain in the ground are those classified as hardy by the RHS: royal lily (Lilium regale, H6), crocosmia 'Lucifer' (H5), nerine (Nerine bowdenii, H5), arum (Zantedeschia aethiopica, H4), and Byzantine gladiolus (Gladiolus communis subsp. byzantinus). Most lilies are hardy and require no special care in winter, according to the RHS.
Common crocosmias are hardy in warm, sheltered conditions; in colder regions, cover them with a thick layer of compost in late autumn. Be careful with Crocosmia × crocosmiiflora: it spreads easily, and the RHS advises against planting it if your garden borders open countryside. Nerine, planted with the neck out of the ground at the foot of a sunny wall, flowers in autumn as temperatures drop.
❄️ Lifting and overwintering tender summer bulbs
Tender summer bulbs, dahlias, tuberous begonias, hybrid gladioli, freesias and cannas in colder regions, are lifted in autumn and stored in a dry, frost-free place. For dahlias, the RHS recommends lifting after the first frost has blackened the foliage, and no later than late November, then storing them in a cool, dark, frost-free place.
In milder regions, you can leave them in place under 15 cm of mulch, with a risk in very cold or very wet winters. Tuberous begonias are ideally kept at 7°C, gladiolus corms in cool boxes, and freesias in a warm place, around 26°C, according to the RHS.
The full step-by-step guide is in our full dahlia guide and our guide to protecting plants from frost.
🪴 Summer bulbs in pots: useful tips
In pots, most summer bulbs do very well, provided they are in a container with drainage holes, a well-draining growing medium, and planted slightly closer together than in the ground. The RHS recommends planting in pots at a depth of three times the height of the bulb, leaving a space between bulbs equal to the width of a bulb, in a mixture of three parts peat-free compost to one part gravel.
Allow at least a 30 cm wide pot for a canna and 20 to 23 cm in diameter for an agapanthus. Water once after planting, then only when the growing medium is dry 2 to 3 cm deep.
All our tips for growing in pots are in our guide to planting bulbs in pots.
🗓️ Summer bulbs through the seasons
A summer bulb needs water during its growth, a stake if it is tall, and then a decision in autumn: leave it in place or lift it. Always let the foliage yellow before cutting it: this is what recharges the bulb for the following year.
This process is explained in detail on our page what to do with bulbs after flowering.
📅 Seasonal care calendar
| Season | Key action |
|---|---|
| 🌸 Spring | Planting from March to May: agapanthus, gladioli, dahlias in the ground; cannas and begonias started indoors |
| ☀️ Summer | Flowering; watering by feel, stakes for tall dahlias and gladioli, deadheading |
| 🍂 Autumn | Nerine flowering; lifting hybrid gladioli, then dahlias after the first frost (no later than late November, RHS) |
| ❄️ Winter | Storing tubers and corms frost-free; deciduous agapanthus covered from November to early April, African agapanthus brought indoors frost-free (RHS) |
🐛 Errors to avoid with summer bulbs
Failures with summer bulbs almost always stem from planting too early, soil that is too wet, or not preparing properly for winter.
| Error | Why it is a problem | The solution |
|---|---|---|
| Planting tender bulbs too early | Dahlias and begonias are not hardy, cannas are only slightly hardy (H3, RHS) | Wait until the end of the frosts, or start indoors |
| Planting a lily in heavy clay | Lilies do not grow well in heavy, poorly drained or waterlogged soil (RHS) | Deep, well-drained pot, or raised bed |
| Burying the neck of the nerine | The RHS recommends a neck visible above the ground | Bulb neck out of the ground |
| Leaving hybrid gladioli outdoors in colder regions | They are not fully hardy (RHS) | Lift in late summer or early autumn |
| Planting Crocosmia × crocosmiiflora near open countryside | It spreads too easily (RHS) | Avoid it near open countryside, lift excess corms without composting them (RHS) |
| Cutting green foliage | The bulb does not recharge for the following year | Wait until it yellows |
🌿 Our summer bulbs and their guides
Each genus in this guide has its own guide or tips, and our bulbs to plant in spring are gathered in a collection.
| Genus or guide | Our selection |
|---|---|
| Dahlia | The whole growing process, from tuber to overwintering: our full dahlia guide |
| Agapanthus (Agapanthus) | African agapanthus in 11 cm pots, evergreen and H3: in a large pot in the sun, brought indoors frost-free in colder regions. Our blue agapanthus, our white agapanthus 'Albus' or our agapanthus mix, and our agapanthus guide |
| Ranunculus (Ranunculus asiaticus) | Our florist ranunculus mix or our pastel mix, with our ranunculus guide |
| Freesia | Fragrant, at the border or in a sunny pot: our double freesia mix |
| Summer bulb mixes | For a sunny bed, our bulb mix for sunny gardens; for a cool spot, our bulb mix for damp gardens |
| When and how to plant bulbs | Planting depths and directions for all bulbs, among our flowering bulbs |
🔍 Summer bulbs and autumn bulbs: do not confuse them
Some bulbs flower in early summer but are planted in autumn: this is the case of ornamental garlic, which the RHS recommends planting in September and October. Conversely, true summer bulbs, dahlias, gladioli, cannas or begonias, are planted in spring.
If you are looking for what to plant from September to November, see our bulbs to plant in autumn.
✅ Our tips for successful summer bulbs
To succeed with your summer bulbs, choose them according to your soil, plant them from March to May at a depth of two to three times their height, and decide on their winter fate at the time of purchase. Hardy ones (lilies, crocosmia, nerine, arum) stay in place; tender ones (dahlia, begonia, hybrid gladiolus, freesia) are lifted in autumn.
Find our bulbs to plant in spring, our full sun plants, our outdoor flowering plants and our shade and cool plants.
For a first summer bulb bed, I recommend mixing a genus that stays in place, such as crocosmia or royal lily, and a spectacular genus that is lifted, such as dahlia. This way you enjoy a bed that returns on its own every year, without giving up on large flowers. My favourite thing is still to start cannas and begonias indoors in March: you gain many weeks of summer flowering.
Laura Bruneau
Jardinière & autrice
