With their striking spikes of vibrant flowers gladiolus are a summertime garden favorite. But did you know you can get a jumpstart on gladiolus season by growing these bulbs indoors? Starting glads inside lets you enjoy their blooms weeks earlier than normal planting time.
Follow this guide to discover how to successfully grow gladiolus indoors for an early start.
Why Start Gladiolus Indoors?
Growing gladiolus indoors offers several advantages:
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Enjoy flowers earlier – Blooms can arrive 4-6 weeks sooner than outdoor planting,
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Lengthen bloom time – Stagger indoor plantings for successive glad flowering
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Guarantee blooms – Great for short-season climates where frost may claim outdoor glads.
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Evaluate varieties – Test new ones indoors before planting outdoors.
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Add color indoors – Use forced glads as temporary living room decor.
When to Start Gladiolus Inside
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Start glads indoors 4-6 weeks before your average last spring frost date.
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Allow sprouted bulbs to grow indoors for 4-5 weeks before moving outside.
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Plant outdoor glads when nighttime temps remain above 60°F.
Supplies Needed
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Gladiolus bulbs – Purchase bulbs or use stored bulbs from last year.
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Container – Shallow trays, pots, or buckets work well.
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Potting mix – Use a well-draining mix for starting seeds or bulbs.
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Water – Use room temperature water for indoor forcing.
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Bright, indirect light – A sunny window or grow lights.
Step-By-Step Growing Guide
Follow these steps for successfully growing gladiolus indoors:
1. Prepare Bulbs
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Select plump, blemish-free bulbs that haven’t sprouted yet.
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Optional: Soak bulbs in room temperature water overnight to pre-sprout.
2. Plant in Containers
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Fill container with moist potting mix.
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Plant bulbs 2-3 inches deep and 1-2 inches apart, pointed end up.
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Water soil until moist but not saturated.
3. Provide Warmth & Light
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Place containers in warm indoor spot (65-75°F).
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Provide bright, indirect light from a south window or grow lights.
4. Keep Moist & Monitor Growth
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Check soil moisture daily and water as needed to keep damp but not wet.
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Watch for sprouts in 2-3 weeks.
5. Harden Off & Plant Outdoors
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Gradually introduce to outdoor conditions over 7-10 days.
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Plant sprouted bulbs outdoors when soil warms above 60°F.
Growing Medium Options
Soil
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Plant bulbs in pots or trays filled with moist, well-draining potting mix.
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Keeps bulbs stable and provides nutrients for growth.
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Requires more space than water forcing.
Water
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Place bulbs close together in shallow water, just covering base.
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Simple, space-saving option. Roots grow quickly in water.
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Change water every 2-3 days to prevent rotting.
Troubleshooting Issues
Leggy growth – Insufficient light. Move to brighter area or use grow lights.
Rotting bulbs – Overwatering. Allow soil to partially dry between waterings.
Tipping over – Stake tall, floppy stems for support.
Few or no blooms – Inadequate chill period. Store bulbs properly after digging.
Misshapen flowers – Extreme temperature changes. Keep indoor growing area stable.
Growing Gladiolus Year-Round
By starting glads at strategic intervals, you can enjoy their blooms nearly year-round:
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January – Force bulbs for mid-late spring blooms.
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March – Start bulbs for early summer blooms.
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May – Plant outdoors for mid-late summer bloom.
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July – Start bulbs for late fall blooms indoors.
With the simple process of forcing bulbs indoors, you can brighten up the colder months with gladiolus blooms. It just takes a little planning and preparation. Give it a try this year and see how early you can enjoy armloads of colorful gladiolus flowers!
How to Start Gladiolus Indoors
To be clear, gladiolus have corms, not bulbs. But many gardeners refer to them as “bulbs,” so we’ll being using the terms interchangeably in this guide.
Spring can’t come early enough, as far as I’m concerned. So let’s not wait one minute more!
Four to six weeks before the last predicted frost date in your area, prepare the corms.
Getting bulbs ready to plant is important whether you’re planting new ones or replanting ones you took out in the fall and stored.
If you’re looking to buy something new, it pays to look around. Some stores won’t have gladiolus in stock during the off season, but others will.
Eden Brothers, for example, carries a fantastic range, from the tricolored pink, pale yellow, and creamy white ‘Mon Amour’ to the blood-red ‘Black Star.’
Or maybe you want a mixture of colors. If so, visit Burpee for a Glamini mix in yellow, red, purple, and white.
Brush off any dirt from the overwintered bulbs with a soft, dry brush. Divide up any large clumps. Purchased bulbs should be clean and already divided up for you.
You can optionally set the corms in water overnight to encourage them to open up and start growing.
Either submerge them entirely or just set the base in the water. This just speeds up the sprouting process, but it’s not essential.
Fill a flat or a container that’s at least eight inches deep with fresh, water-retentive potting mix.
If you have lots of gladiolus corms, consider using a large storage bin – 18-gallon or larger. Just make sure you put it down before you fill it up, because it will be heavy to move.
If you don’t have anyone to help you move the container, you might want to put it on wheels or in a wagon.
If you want the corms to grow well, you should plant them about two to four inches deep, or twice as deep as the length of the corm. Make sure the pointy end is facing upwards.
Water the medium well so that it’s moist but not soaking wet or soggy.
Put the pot somewhere warm and sunny inside that gets at least six hours of direct sunlight every day. Make sure the soil stays moist.
You can also use supplemental lighting if you don’t have an area with enough exposure.
Allow the top inch of the soil to dry out between watering.
When using a big storage container, be careful not to add too much water. It’s easy for the soil at the bottom of the container to become soggy, which can cause it to rot.
Within a few weeks to a month, you should see new growth popping out of the soil.
The gladiolus plants can go outside as soon as it’s at least 60°F at night and they have at least three leaves.
Before you can plant them and enjoy their beauty, you need to “harden” them off. This is because they’re used to living in a soft environment inside.
To get them used to being outside, move the growing container to the spot where the gladiolus will be planted and leave it there for a while. Leave the pot there for an hour and then bring it back inside.
The next day, leave it out there for two hours before bringing it in.
If you used a big storage container, you’ll need a strong-backed helper. After your workout, you can probably skip ab day.
Keep adding an hour each day until the plants can stay outside for a full eight hours.
At this point you can transplant your gladiolus.
Prepare the planting area by digging enough holes for all your corms. You should dig a bigger hole than you think you’ll need so you don’t have to force the corm into it.
Gently push your hands into the soil and dig down underneath the roots of each plant. Even though you can use a trowel, I like to dig with my hands because I can feel the roots better and I don’t hurt them.
Lift the gladiolus out of the soil and place it in the ground. The corm should be sitting at the same depth as it was in the growing container. Repeat until all your corms are in the ground.
Firm the soil up around the corms and water in well. You might need to add a little more soil if it settles.
Learn how to grow and take care of this beautiful plant by reading our complete guide to growing gladiolus.
Gladioli Edition: Starting Gladioli Indoors for Earlier Blooms & Planting Outdoors – UK
FAQ
How do you grow gladiolus in pots indoors?
Can you keep gladiolus inside?
Is gladiolus indoor or outdoor?
Do gladiolus flowers come back every year?
Can Gladiolus grow indoors?
Little do most know, you can actually start gladiolus indoors in pots early, just like you may do with your vegetable plants. You can start your gladiolus corms indoors about four weeks before your last frost date. Gladiolus can be started in either soil or water. Which method you use for starting your gladiolus early is up to you.
How do you grow a Gladiolus?
Lift the gladiolus out of the soil and place it in the ground. The corm should be sitting at the same depth as it was in the growing container. Repeat until all your corms are in the ground. Firm the soil up around the corms and water in well. You might need to add a little more soil if it settles.
Can Gladiolus grow in containers?
In addition to garden cultivation, you may also plant your gladiolus in containers, with a depth of 12 inches, which allows room for the roots to grow. Lift the corms at season’s end for winter storage, as containers get colder than ground soil, and they may freeze.
When should I start my gladiolus corms indoors?
Starting your gladiolus corms indoors a little early is a great way to get a jump start on the season. By starting gladiolus indoors, you can be enjoying lovely gladiolus flowers when your neighbors still only have leaves.