With a wide range of colors, bloom sizes, and plant sizes, petunias are a top choice for many gardeners. They grow incredibly well in containers, flower beds, landscapes, and hanging baskets. No matter where you choose to grow petunias, they will provide endless displays of blooms, even in the heat of summer.
It’s inevitably easier to plant potted petunias than to start from seed. Purchasing four cells or potted petunias works if you are growing smaller amounts. But if you need to plant mass amounts of petunias, planting them by seed is a preferred method.
Garden centers and nurseries only carry so many petunia varieties in containers. If you are after a specific variety that is less popular or garden centers don’t carry, planting by seed is your best option.
If you need to plant a large number, are looking for a specific variety, or you simply love growing something from start to finish, consider growing petunias by seed. Follow the simple instructions outlined in this article to get started!
Petunias are one of the most popular annual flowers for gardens. With their wide array of bright colors and reliable performance, it’s no wonder petunias have been a summertime favorite for decades.
Most gardeners buy petunia transplants from nurseries in spring. However, starting petunias from seed indoors provides some great advantages:
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Access to more unique, heirloom and specialty varieties available only by seed
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Much lower cost than buying individual plants
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Stronger healthier transplants with well-developed root systems
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Earlier bloom time and longer flowering period
Growing petunias from seed is an easy, rewarding task for both beginners and seasoned gardeners. Here is a complete step-by-step guide to successfully raise vigorous petunia transplants indoors.
When to Start Petunia Seeds
Petunia seeds should be started indoors 6-8 weeks before your anticipated outdoor planting date after your last expected spring frost This gives the seeds enough time to germinate and seedlings adequate time to mature into compact, bushy transplants ready for the transition to the garden
As a general timeline, aim to sow petunia seeds in late February to March for transplanting outdoors in May in most regions. Adjust your starting schedule accordingly based on your specific spring frost dates and growing zone.
Choosing Containers for Starting Seeds
You’ll need clean containers or cell packs with drainage holes for starting petunia seedlings. Good options include:
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Cell packs or plug trays – Most efficient use of space, come in various cell counts
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Peat or paper pots – Minimize root disturbance at transplanting
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Planter flats – Allow even spacing between seedlings
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DIY containers – Can use eggs cartons, trays or pots by punching holes yourself
Be sure to thoroughly clean and sanitize any used containers by soaking in a 10% bleach solution for 10 minutes. This prevents any disease transmission to vulnerable seedlings.
Selecting a Seed Starting Mix
Use a sterile, soilless seed starting mix to start petunia seeds. This type of germinating medium is lightweight and fine-textured, which makes it easy for delicate new seedlings to develop roots.
You can purchase high quality premade blends, or make your own by combining:
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Peat moss or coco coir – Absorbs and retains moisture
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Perlite or vermiculite – Improves drainage and aeration
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Compost – Adds nutrients and organic matter
Avoid regular potting soil, which is too dense and may contain weed seeds, pests or pathogens. I recommend mixing in some extra perlite to enhance drainage and prevent fungal issues.
Filling Containers and Planting Seeds
Here are the step-by-step instructions for sowing petunia seeds:
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Moisten your seed starting mix until damp but not completely soaked. Allow any excess water to drain out.
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Gently but firmly fill your cell packs or containers with the moistened mix up to the brim. Smooth and level the surface.
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Very lightly sprinkle your petunia seeds on top of the soil. Petunias need light exposure to germinate so do not cover them.
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Gently press the seeds into the mix so they make good contact with the medium below.
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Mist gently with water to further settle seeds. Be careful not to saturate.
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Optional – Top dress with a thin layer of vermiculite to help retain moisture around seeds.
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Cover trays with plastic dome lids or plastic wrap to maintain humidity.
Caring for Seeded Trays
Once sown, petunia seed trays must be cared for very diligently to create ideal germinating conditions:
Temperature – Maintain a consistent soil temperature of 70-75°F. Use a heat mat if needed.
Light – No light is required until after seeds sprout. Move to bright light immediately after germination.
Moisture – Keep seeds consistently damp, but not soaked. Gently mist surface when dry.
Humidity – High humidity is critical. Ensure trays are domed or wrapped.
Ventilation – Once sprouts emerge, remove domes and increase air flow to prevent fungal diseases.
When to Expect Germination
With proper care and moisture, most petunia seeds will begin to germinate within 7-14 days. Timing varies based on soil temperature, seed age and variety.
Make sure to check under any emerging seedlings daily once the 7 day mark hits – gently stir the top of the soil with your finger to uncover any sprouts developing underneath.
Promptly removing humidity domes prevents mold from forming on tender new seedlings at this stage.
Caring for Petunia Seedlings
After those first eager sprouts emerge, petunia seedlings require bright light, cooler temps, adequate moisture and good air circulation:
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Lighting – Provide 14-16 hours under grow lights or a very sunny south window.
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Temperature – Move to 60-70°F room. Avoid heat buildup and stem stretching.
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Watering – Allow starting mix to dry out slightly between waterings. Avoid excess moisture.
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Fertilizer – Begin mild fertilization once true leaves form. Use 1/4 strength soluble plant food.
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Spacing – Thin overcrowded groups to 1-2 seedlings per cell. This prevents competition.
Hardening Off Petunia Seedlings
Hardening off is the process of gradually acclimating tender indoor-raised transplants to outdoor growing conditions over 7-10 days. This toughens up the plants, prevents transplant shock and helps them establish more quickly.
To properly harden off petunia seedlings:
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Move pots to a sheltered shaded spot outdoors for a few hours, gradually increasing time over days.
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Bring plants back indoors each night until risk of frost has passed.
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Allow plants to experience partial sun, wind, cool nights and light rain.
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Reduce watering slightly to slow growth during this hardening off period.
Transplanting Petunias Outdoors
Once properly hardened off and after your last average spring frost date has passed, it is safe to transplant petunia seedlings into the garden. Here are some tips for this transition:
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Make sure plants are properly hardened off for 7-10+ days before transplanting.
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Water seedlings thoroughly both the day before and the day of planting.
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Carefully tease apart any root bound plants before going into the ground.
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Dig holes the same depth as pots and adjust soil level accordingly.
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Water newly planted transplants regularly for the first few weeks until roots expand into surrounding soil.
Growing Tips for Success
Follow these key tips to get the very most out of your homegrown petunias all season long:
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Pinch back leggy or stretching seedlings to encourage bushiness.
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Deadhead spent blooms regularly to promote new flowering.
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Fertilize every 2-3 weeks with a balanced flower fertilizer once established.
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Monitor for common pests like aphids, thrips and spider mites.
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Avoid overhead watering late in day – wet foliage is susceptible to disease.
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Place in full sun – minimum 6 hours for best growth and maximum flowers.
With proper care when starting seeds and hardening off, homegrown petunia transplants will thrive and reward you with vivid, bountiful flowers all season long. Give it a try this year – you may never go back to buying plants at the nursery again!
Step 1: Choose Your Variety
There are many different types of petunias to choose from.
The hardest part of growing petunias is choosing a variety to grow. There are hundreds of varieties to choose from, and this can be overwhelming, especially for new gardeners. You will first have to decide if you want a mounding variety or trailing variety.
Trailing varieties are great in hanging baskets and containers. As an added bonus, they are self-cleaning. These petunias will cascade down the sides of the container, rock walls, or even trail up a trellis. You can keep trailing varieties shorter by pruning during the season.
Mound varieties are excellent choices in flower beds, containers, landscapes, and vegetable gardens. They don’t spread like trailing varieties and stay in a nice compact mound for their life cycle. Mounding varieties look great when planted in masses and blanket areas very nicely.
Another thing to consider is you can find seeds in pelleted and non-pelleted form. The seeds are very, very tiny and can be difficult to handle. Pelleted petunias are easier to see and handle during planting. The coating on the pellet will dissolve over time.
Step 3: Planting Seeds
Start planting your petunia seeds by filling pots or cells with potting soil.
Once you have gathered your materials, you can begin to plant your seeds. You should start planting seeds 10 to 12 weeks before the anticipated last frost of the spring. Begin by filling pots or cells with potting soil. Once they are filled, lightly press the seeds into the soil. They should be just below the soil surface.
Once the seeds are planted, lightly water until the soil is moist. Misting the soil works best because pouring water over the seeds can cause them to shift. Label each container, so you know the variety of each container.
Once watered and labeled, cover the seeds with a plastic dome or plastic wrap. This will help keep temperatures high so seeds can germinate. We want temperatures during germination to be around 75 F to 85 F. If you have a heat mate, this will be beneficial to keep temperatures high during germination.
Place containers in indirect sunlight for at least 6 hours a day. If you are placing your petunias under grow lights, be sure the lights are 4 to 6 inches above the containers. You can move these lights up as the seedlings grow.
✅ How to Grow Petunias from Seed – Start to Finish.
FAQ
Is it hard to grow petunias from seed?
- Start indoors: Petunias are heat-loving plants, so start seeds indoors 8-10 weeks before your last expected frost.
- Choosing the right soil: Use a good quality seed-starting mix or a light, sandy soil.
- Seed size and handling: Petunia seeds are very fine and require careful handling. Consider using pelleted seeds for easier handling, if available.
How early should I start petunia seeds indoors?
Timing. Sow petunia seeds indoors about 10 weeks before the intended outdoor planting date. (Petunias should be planted outdoors after the danger of frost is past.)
Do you soak petunia seeds before planting?
Petunia seeds do not require any treatment (eg soaking, stratification) before sowing.
How do you plant Petunia seeds?
Petunia seeds are small and require adequate care when planting. To plant the seeds, use a stick to carefully press the seeds carefully on the surface of the soil. Now, petunia seeds are very light to germinate, so do not bury them deep into the soil. You can lightly cover them with soil instead.
How to grow Petunia seeds indoors?
To start your petunia seeds indoors, Grow Petunias Inside you will need the following supplies: While petunias are widely available in plant nurseries and garden centers, Grow Petunias Inside there are several benefits to growing them from seeds indoors. For one, it allows you to have a wider selection of petunia varieties to choose from.
How long does it take for petunias to grow?
They will be set up on a table beneath my deck, where they will receive brilliant light but not direct sunlight and where it is cooler in the summer. In three to four weeks, expect to see roots. Soon enough, you’ll be able to fill a tub or other container with your lovely petunias.