How to Grow Sweet Peas from Seed Indoors

Dreaming of armfuls of fragrant sweet peas and early summer? The secret starts months earlier…indoors. In this post, I’ll show you exactly how to grow sweet peas from seed indoors, when to start them before your last frost, and how to raise strong seedlings ready for the garden.

I’ve been starting sweet peas inside for years in my cut flower garden, and giving them that early head start makes all the difference. Let’s walk through the simple steps that lead to healthier vines and more blooms.

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Sweet Pea Basics (Quick Facts)

When to Start Growing Sweet Peas from Seed Indoors

In my experience, timing is everything with sweet peas. The earlier they are established in cool weather, the happier they are.

Sweet peas can be sown in the fall in warmer regions with milder winter weather (zone 7 and above). For everyone else, sow your sweet peas in late winter or early spring.

These plants like cool temperatures, so in my Zone 8B garden, I like to start my sweet peas indoors about 10-12 weeks before our last frost date, while the weather is still cool and unpredictable. You can also find this information on your seed packets.

Sweet peas can also be sown directly in the ground as soon as the soil can be worked in the spring. The optimum soil temperature for sowing sweet pea seeds is 55-65°F. Watch for birds, snails, slugs, and other pests that love sweet peas.

NOTE: Sweet peas are poisonous if ingested. Use caution around children and pets.

Supplies for Growing Sweet Peas from Seed Indoors

How to Grow Sweet Peas from Seed Indoors (Step-by-Step)

Starting sweet peas indoors gives them the cool conditions they love and lets you control soil quality, moisture, and root development from the very beginning. A strong start indoors leads to sturdier vines and earlier blooms in the garden.

Step 1 – Soak the Seeds (Optional but Helpful)

Sweet peas have a hard outer shell. Soaking them in room-temperature water for up to 24 hours softens the seed coat and can speed up germination.

They will sprout without soaking, but I’ve found that it usually cuts off a few days, especially when starting seeds in late winter.

Step 2 – Choose Deep Containers

Sweet peas form long roots very early in their growth. Shallow trays can restrict that development.

Use:

The first year I grew sweet peas, I used shallow seed trays, and they definitely let me know that they weren’t impressed.

The deeper the container, the stronger and less stressed your seedlings will be at transplant time.

Step 3 – Use a Quality Seed Starting Mix

Fill containers with moist, well-draining seed-starting mix.

A good seed mix:

To stretch your supplies, fill the bottom half of the pot with regular potting soil and use seed-starting mix where you’re sowing the seeds.

Step 4 – Sow the Seeds

Plant two seeds per container about 1/2 inch deep. Cover lightly and gently firm the soil.

If both seeds sprout, you can thin the weaker one later, or leave both if they’re growing well.

Step 5 – Bottom Water

Place containers in a tray with about 1 inch of water and allow the soil to absorb moisture from the bottom. Do not leave them sitting in water longer than an hour.

Bottom watering keeps the surface soil from crusting over and avoids disturbing the seeds.

Step 6 – Provide Cool, Bright Conditions

Cover with a humidity dome until seeds germinate, then remove it immediately.

Sweet peas prefer cool growing conditions. A cool greenhouse, an unheated garage space with grow lights, or a bright window works great.

I’ve found that sweet peas grown in cooler conditions develop thicker stems and sturdier growth than those kept too warm indoors.

What to Do Once Sweet Peas Germinate

Hardening Off Sweet Peas Before Transplanting

Before moving your sweet pea seedlings into the garden, they need time to adjust to outdoor conditions.

Start with a few hours in a sheltered location, slowly increasing their exposure each day.

About 7-10 days before planting, begin hardening them off by gradually exposing them to the outdoor temperatures, sunlight, and wind. This gradual transition reduces transplant shock and helps seedlings develop stronger stems.

Preparing Garden Beds for Sweet Peas Started Indoors

While your seedlings are hardening off, prepare their permanent growing space.

Choose a location that receives at least 6 hours of sunlight daily. In warmer climates, morning sun with light afternoon shade helps protect blooms from heat stress.

Sweet peas thrive in rich, well-draining soil. Before planting:

Install your trellis, fencing, or support structure now, before planting, to avoid disturbing roots later. Sweet pea vines grow quickly and need sturdy vertical support from the beginning.

Transplanting Sweet Pea Seedlings to the Garden

Sweet peas can be transplanted around your last spring frost date, while temperatures are still cool.

Plant in the early morning or late evening to reduce stress from the sun and heat.

Space seedlings about 8 inches apart, planting one row on each side of your trellis for even coverage.

Water thoroughly after planting to settle the soil around the roots.

Once established, your sweet peas will begin climbing quickly, and with consistent care, buds will soon follow. Watching those first vines grab onto the trellis is always one of my favorite early-spring garden moments!

Feeding Sweet Peas for strong Growth and Blooms

Sweet peas are heavy feeders, especially once they begin climbing and setting buds. Giving them rich soil from the start makes all the difference.

Before Planting Outdoors

Sweet peas thrive in fertile, well-draining soil.

Work compost or well-rotted manure into the soil before transplanting. You can also mix in bone meal to support strong root development and flower production.

During the Growing Season

Optional Boost

Seaweed emulsion can be used occasionally throughout the season to support overall plant health and soil vitality.

Caring for Sweet Peas Throughout the Season

Once your sweet peas are established in the garden, consistent care will reward you with strong vines and continuous blooms.

Watering

Sweet peas like evenly moist soil, especially during warm weather.

Water deeply once a week, and more often during dry spells. The goal is moist soil, not soggy roots. Adding mulch around the base of the plants helps retain moisture and regulate soil temperature.

Avoid overwatering when possible to reduce the risk of fungal disease.

Pinching for Fuller Plants

If you started pinching your sweet peas when they were seedlings, you’re already ahead. But even once they’re planted in the garden, a little continued pinching early in the season helps keep plants full and productive.

If a stem starts racing upward with one tall central line, go ahead and pinch just above a set of leaves to encourage more side shoots. These shoots mean more flowering stems and more bouquets.

Once the plants are actively blooming, regular harvesting takes over, encouraging even more growth.

Providing Strong Support

Sweet peas are vigorous climbers and can grow over a foot per week during peak season.

Install trellises, netting, or fencing at planting time so vines have something to grab onto immediately. Waiting too long can damage roots and stems.

Tie vines loosely with twine as they grow.

Harvesting and Deadheading

There’s nothing quite like bringing in a handful of sweet peas and catching that fragrance every time you walk by.

Frequent harvesting is one of the best ways to extend the bloom season. Pick flowers when at least two buds at the tip are still unopened for the longest vase life (usually 4-5 days).

Remove spent blooms regularly to prevent the plant from setting seed too early.

Save Seeds for Next Year’s Garden

You can save the seeds in each sweet pea pod to grow next year.

Common Mistakes When Growing Sweet Peas

Even experienced gardeners run into trouble with sweet peas. Here are a few of the most common mistakes to avoid:

Final Thoughts for Growing Sweet Pas from Seed Indoors

Starting sweet peas indoors might not feel very exciting in the middle of winter, especially when everything outside is still cold and gray. But there’s something so hopeful about those first little seeds growing undercover.

Give them that cool start and a little steady care, and before you know it, they’ll be climbing their trellis and filling your garden (and your kitchen) with the sweetest fragrance. There’s nothing quite like cutting that first bouquet of the season and realizing the tiny seeds you planted months ago made it all the way here.

If you’ve never grown sweet peas from seed indoors before, I hope this gives you a little confidence to try. And if they’re already a favorite in your garden, you know just how special that first harvest feels every single year.

If you found this post helpful, feel free to share it with a fellow gardener who’s also dreaming about sweet peas this season.

Until next time,

Happy Gardening!

I’m a self-taught hobby gardener. Everything I share on my blog is my opinion and what has worked for me.