Summer-blooming bulbs should go into the ground after the danger of frost has completely passed. Knowing exactly when to plant bulbs for summer can make the difference between a vibrant garden and a disappointing one. This guide walks you through every step, from soil temperature checks to regional timing tips.
Most summer bulbs are tender, meaning they cannot survive freezing temperatures. If you plant them too early, cold soil can rot the bulbs before they sprout. Wait until the soil has warmed up to at least 60°F (15°C) at a depth of 4 inches.
Your local last frost date is the key reference point. For most regions, this falls between late March and mid-May. After that date, you can safely begin planting.
When To Plant Bulbs For Summer
The exact timing varies by your climate zone and the type of bulb you choose. Below, we break down the best planting windows for common summer bulbs.
General Timing By Climate Zone
Use your USDA hardiness zone as a rough guide. Zones 3-5 have shorter summers, so plant as soon as the soil is workable after the last frost. Zones 6-8 enjoy a longer window, from early April to mid-June. Zones 9-10 can plant from late winter through early summer, but avoid the hottest months.
- Cold climates (Zones 3-5): Plant from late May to early June.
- Temperate climates (Zones 6-8): Plant from mid-April to late May.
- Warm climates (Zones 9-10): Plant from February to April for early blooms, or again in late summer for fall flowers.
Bulb-Specific Planting Times
Not all summer bulbs have the same needs. Here are the most popular ones and their ideal planting months.
Dahlias
Dahlias are frost-tender and need warm soil. Plant them about two weeks after your last frost date, when the soil temperature is consistently above 60°F. In cooler zones, you can start them indoors in pots 4-6 weeks before the last frost, then transplant them outside.
Lilies
Lilies are more forgiving than dahlias. They can be planted in spring as soon as the ground is thawed and workable. For a longer bloom season, plant a mix of early, mid, and late-season varieties at the same time.
Gladiolus
Gladiolus corms are planted every two weeks from the last frost date until early summer. This staggered planting ensures continuous blooms from July to September. Each planting will flower about 70-90 days later.
Begonias and Caladiums
These shade-loving bulbs need warm soil and consistent moisture. Plant them after all frost danger has passed, usually in late spring. In northern zones, start them indoors 6-8 weeks before the last frost for earlier blooms.
Elephant Ears and Cannas
These tropical bulbs thrive in heat. Wait until nighttime temperatures stay above 50°F. In most regions, this means planting in late May or early June. They grow fast once the soil warms up.
How To Check Soil Temperature
Soil temperature is more reliable than calendar dates. Here is a simple method to check it.
- Use a soil thermometer inserted 4 inches deep into the ground.
- Take the reading in the morning, before the sun heats the surface.
- Measure at three different spots in your garden and average them.
- Wait until the average is at least 60°F for most summer bulbs.
If you do not have a thermometer, you can use a hand test. Dig down 4 inches and grab a handful of soil. If it feels cool but not cold, and crumbles easily, it is likely warm enough. If it feels wet and clumpy, wait a few more days.
Regional Planting Guide
Your local climate dictates the best planting window. Here is a breakdown by region.
Northeast And Midwest
Last frost dates range from late April to late May. Plant tender bulbs like dahlias and gladiolus after mid-May. For lilies, you can plant as early as mid-April if the soil is workable. Use raised beds or black plastic to warm the soil faster.
Pacific Northwest
Cool, wet springs are common here. Wait until May or even early June for soil to dry out and warm up. Bulbs like begonias and caladiums do well in the region’s mild summers. Avoid planting in soggy soil to prevent rot.
Southeast And Gulf Coast
Warm winters mean you can plant as early as February or March. However, summer heat can stress bulbs. Plant early-blooming varieties like calla lilies and gladiolus in late winter. For later blooms, plant in August for fall flowers.
Southwest And Desert
Intense heat and dry soil require careful timing. Plant in early spring, from February to April, before the scorching summer arrives. Use mulch to keep soil cool and moist. Some bulbs, like agapanthus, can be planted in fall for spring blooms.
Mountain And High Altitude
Short growing seasons with late frosts are typical. Plant tender bulbs in late May or early June. Consider pre-sprouting indoors to gain a few weeks. Hardy lilies can be planted earlier, as soon as the soil is thawed.
Step-By-Step Planting Process
Once you know when to plant, follow these steps for the best results.
- Prepare the soil: Loosen the soil to a depth of 12 inches. Mix in 2-3 inches of compost or well-rotted manure for nutrients and drainage.
- Check drainage: Summer bulbs hate wet feet. If your soil is heavy clay, plant in raised beds or mix in sand and organic matter.
- Plant at the right depth: A general rule is to plant bulbs at a depth three times their height. For example, a 2-inch tall bulb goes 6 inches deep.
- Space properly: Follow the label spacing. Crowded bulbs compete for nutrients and produce smaller flowers.
- Water thoroughly: After planting, water deeply to settle the soil. Do not water again until you see growth, unless the soil is very dry.
- Mulch: Apply a 2-inch layer of organic mulch to keep soil cool and moist. This also suppresses weeds.
Common Mistakes To Avoid
Even experienced gardeners make errors. Here are the most common ones with summer bulbs.
- Planting too early: Cold, wet soil rots bulbs. Always wait for proper soil temperature.
- Planting too deep or too shallow: Depth affects blooming. Too deep, and bulbs may not emerge. Too shallow, and they may dry out.
- Overwatering: Bulbs store water and nutrients. Too much water causes rot. Water only when the top inch of soil is dry.
- Ignoring sunlight needs: Most summer bulbs need full sun (6-8 hours daily). Shade-loving bulbs like begonias need partial shade. Check the label.
- Forgetting to harden off: If you started bulbs indoors, gradually expose them to outdoor conditions over a week before planting.
Tips For Extending Bloom Time
You can enjoy flowers from early summer to fall with a few simple strategies.
- Stagger planting: Plant gladiolus, lilies, or dahlias every two weeks for continuous blooms.
- Deadhead regularly: Remove spent flowers to encourage more blooms. This prevents the plant from going to seed.
- Fertilize lightly: Use a balanced, slow-release fertilizer at planting time. Avoid high-nitrogen fertilizers, which promote leaves over flowers.
- Choose early and late varieties: Mix early-blooming lilies with late-blooming dahlias for a long season.
- Lift and store tender bulbs: In cold climates, dig up dahlias, cannas, and gladiolus after the first frost. Store them in a cool, dry place for next year.
Indoor Starting For Short Seasons
If you live in a zone with a short growing season, starting bulbs indoors gives you a head start. Here is how to do it.
- Choose a container with drainage holes. Fill it with potting mix.
- Plant the bulb at the same depth as you would outdoors.
- Place the container in a warm, bright location. A south-facing window or grow light works well.
- Water sparingly until growth appears. Then water regularly.
- About two weeks before your last frost date, begin hardening off the plants.
- Transplant outdoors after the soil has warmed and all frost danger is gone.
This method works especially well for dahlias, cannas, and elephant ears. It can add 4-6 weeks to your growing season.
Storing Bulbs Before Planting
Sometimes you buy bulbs before the planting window opens. Proper storage keeps them healthy.
- Keep bulbs in a cool, dark, and dry place. Ideal temperature is 50-60°F.
- Do not store them in plastic bags. Use paper bags or mesh sacks for air circulation.
- Check bulbs weekly for signs of rot or mold. Remove any damaged ones immediately.
- Do not refrigerate tender bulbs. Cold temperatures can damage them.
If you cannot plant within a few weeks, consider potting them up and growing them indoors until conditions improve.
Frequently Asked Questions
Can I Plant Summer Bulbs In Fall?
No, most summer bulbs are tender and will not survive winter in cold climates. Plant them in spring after the last frost. In warm zones (9-10), you can plant some bulbs in fall for winter or early spring blooms.
What Happens If I Plant Bulbs Too Early?
Cold, wet soil can cause bulbs to rot before they sprout. They may also produce weak growth that is vulnerable to frost. Always wait for proper soil temperature.
How Deep Should I Plant Summer Bulbs?
A general rule is to plant bulbs at a depth three times their height. For small bulbs like crocosmia, plant 3-4 inches deep. For large bulbs like dahlias, plant 6-8 inches deep.
Can I Plant Summer Bulbs In Pots?
Yes, many summer bulbs grow well in containers. Use a pot with drainage holes and quality potting mix. Plant at the same depth as in ground. Water more frequently, as pots dry out faster.
Do I Need To Fertilize When Planting?
A light application of balanced, slow-release fertilizer at planting time helps. Avoid high-nitrogen fertilizers. You can also mix in bone meal for phosphorus, which supports root and flower development.
Final Thoughts On Timing
Getting the timing right for summer bulbs is not complicated. Focus on your local last frost date and soil temperature. When in doubt, wait a week longer than you think. Warm soil rewards you with strong roots and abundant blooms.
Keep a gardening journal to note planting dates and results each year. Over time, you will develop an intuition for your garden’s unique microclimate. With a little patience and these guidelines, you can enjoy a colorful summer garden from June through October.
Remember, the key is to plant after the frost danger has passed and when the soil is warm. Stick to these principles, and your summer bulbs will thrive.