How to Plant Summer Bulbs ([Dahlias](/plants/dahlia-care/), Lilies, Gladiolus)
Summer bulbs -- dahlias, true lilies, gladiolus, cannas, and similar -- are planted in spring after frost danger has passed and bloom from midsummer through fall. Unlike spring bulbs, most summer bulbs originate in tropical or subtropical regions and cannot survive winters in zones 6 and colder.
—- title: "How to Plant Summer Bulbs (Dahlias, Lilies, Gladiolus)" slug: how-to-plant-summer-bulbs hub: care category: "How-To" description: "How to plant dahlias, lilies, gladiolus, and other summer bulbs: timing, depth, spacing, staking, and storage. Step-by-step guide from Extension sources." date: 2026-06-10 updated: 2026-06-10 author: "Thomas A." reading_time: 8 —-
Summer bulbs — dahlias, true lilies, gladiolus, cannas, and similar — are planted in spring after frost danger has passed and bloom from midsummer through fall. Unlike spring bulbs, most summer bulbs originate in tropical or subtropical regions and cannot survive winters in zones 6 and colder without being dug and stored.
The exception is Oriental and Asiatic lilies (Lilium spp.), which are fully hardy to zone 4 and can be left in the ground year-round.
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Dahlias (Dahlia spp.)
Planting time: After last frost, soil temperature minimum 60°F Planting depth: 4–6 inches (measuring to the tuber, not the eye) Spacing: 18–24 inches (dinner-plate types: 24–36 inches) Zones (overwintering): 8–10 in-ground; dig and store in zones 7 and colder
Per Penn State Extension, dahlias are planted with the tuber lying on its side with the growth eye (the small bud at the neck of the tuber) oriented upward or to the side — not straight down. If you cannot identify the eye, orient the neck (thin connector to the main tuber mass) upward.
Staking before planting: Per NC State Extension, place your stake in the planting hole before placing the tuber to avoid spearing the tuber when staking later. Dinner-plate dahlias need a stake of at least 5 feet; medium types need 3–4 feet.
Do not water until shoots appear (approximately 2–3 weeks after planting at optimal soil temperature). Per Penn State, watering before shoot emergence keeps the soil saturated and invites rot. Once shoots emerge, water regularly and deeply.
Pinching: Per Penn State, pinch out the growing tip when dahlia plants are 12–16 inches tall, leaving 3–4 sets of leaves below. This forces side branching and produces more but smaller blooms per plant. Skip pinching for fewer, larger exhibition-type flowers.
Storing Dahlia Tubers
Per Penn State, in zones 7 and colder, dahlia tubers must be dug before hard frost. Wait until the first light frost kills the foliage (this signals the tuber to harden), then cut the stem 2–4 inches above the tuber clump. Shake off loose soil. Allow to air-dry for 1–2 days, then pack in barely moist peat moss or sawdust in a ventilated box. Store at 40–50°F. Do not allow to freeze or to dry completely.
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True Lilies (Lilium spp.)
Planting time: Fall is ideal (October–November) for spring bloom; spring works but delays establishment Planting depth: 3–4 times the bulb's diameter — typically 6–8 inches for large bulbs Spacing: 8–12 inches apart Zones: Hardy to zone 3–4 depending on species; most Asiatic and Oriental lilies are zone 4–8
Per Penn State Extension, true lilies are planted more deeply than other bulbs because the stem above the bulb produces stem roots that provide additional support and nutrient absorption. Shallow planting produces floppy plants that need staking unnecessarily.
Drainage is critical: Per Penn State, lily bulbs rot in waterlogged soil. If drainage is marginal, add a handful of coarse grit under each bulb.
Do not plant in waterlogged clay without amendment. Add coarse perlite or grit to improve drainage in heavy soils.
Species guide:
- Asiatic lilies (June bloom, zones 4–8): No fragrance; red, orange, yellow, pink, white. Very easy to grow.
- Oriental lilies (August bloom, zones 4–8): Intensely fragrant; large white, pink, or bicolor flowers. Slightly more fussy than Asiatics.
- Trumpet lilies (July–August, zones 4–7): Very fragrant; outward-facing trumpets.
- Orienpet ("OT") hybrids (July–August, zones 4–8): Cross between Oriental and Trumpet; very large flowers, easier than pure Orientals.
Per Missouri Botanical Garden, Asiatic lilies are the most reliable and adaptable for most US gardens. Orientals are worth growing for the fragrance if drainage and soil conditions are adequate.
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Gladiolus (Gladiolus spp.)
Planting time: Spring, after last frost, 2 weeks or more after soil reaches 60°F Planting depth: 4–6 inches Spacing: 6 inches apart in rows Zones (overwintering): Zone 7–10 in-ground; dig and store in zones 6 and colder
Per Penn State Extension, gladiolus corms planted 4–6 inches deep produce more stable, less floppy stems than those planted shallowly. For a continuous supply of flowers, succession-plant every 2 weeks from after last frost through early July. The season-long succession extends bloom from July through October.
Staking: Per Penn State, gladiolus stems are prone to falling over in wind. Staking at 3–4 feet is recommended for tall cultivars. Smaller 'Nanus' types (18–24 inches) are self-supporting and better suited for borders.
Storing gladiolus corms: Per Penn State, after the first fall frost kills the foliage, cut stems to 2 inches and dig the corms. Allow to dry in a warm (70–80°F), airy location for 3–4 weeks. Remove the old dried corm from the bottom of the new one. Dust with fungicide powder and store in mesh bags at 35–50°F.
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Cannas (Canna spp.)
Planting time: After last frost, soil 60°F+ Planting depth: 3–4 inches Spacing: 18–24 inches Zones (overwintering): 7b–10 in-ground; dig and store in zones 7 and colder
Per NC State Extension, cannas grow from rhizomes (not true bulbs). Plant horizontally with growth eyes facing up, 3–4 inches deep. They multiply rapidly and need dividing every 2–3 years. Full sun and consistent moisture produce the best flowering. Store overwintered rhizomes in barely moist peat at 45–55°F.
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Frequently Asked Questions
When do I divide lily clumps? Per Penn State Extension, divide lily clumps in fall (after foliage dies) or in early spring before growth begins. Lift the bulb cluster, separate individual bulbs, and replant immediately at the correct depth. Do not leave lily bulbs exposed for more than a few minutes — the scales dry rapidly and reduce establishment success.
Why are my dahlias not blooming? Per Penn State Extension, the most common reasons dahlias fail to bloom are: (1) soil temperature too cold when planted, causing dormancy rather than growth; (2) excess nitrogen from over-fertilization, which promotes foliage at the expense of flowers; (3) planting in partial shade — dahlias need full sun (6+ hours) for full bloom; (4) insufficient water during bud development (July–August).
Can I plant gladiolus in a container? Per NC State Extension, gladiolus can be grown in containers at least 12 inches deep and 12 inches wide for small groups. Use a 5-gallon container minimum per 3–4 corms. Stake firmly — containerized gladiolus are even more prone to wind damage than in-ground plants.
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Recommended gear: Best [dahlia cultivars by size and form](https://outdoorplantcare.com/plants/best-dahlia-cultivars/) — our buyer's guide covering picks for every budget, ranked by Extension publication consensus and personal use.
Sources
- Penn State Extension — Summer-Flowering Bulbs
- NC State Extension — Dahlias and Cannas
- Missouri Botanical Garden — Lilium