Petunia (Petunia × hybrida) is an annual summer flower that is easy to raise from seed at home. The seeds are sown indoors in late February or March, and it takes 10-14 weeks from sowing to the first flower. The plant wants full sun and feeding every week, and it cannot take frost. With the right care it flowers from early summer into October.
Choose a variety by how it will grow
Decide first where the petunia will go, and choose the colour second. A trailing variety needs a hanging basket or window box where the stems can spill over the edge, while a compact variety fills a pot or the front of a border. All five varieties among our petunia seeds are F1 hybrids, grow to around 35 cm tall and are planted 20 cm apart. One seed packet contains 50 seeds.
| Variety | Flower | Habit and position |
|---|---|---|
| Yvette F1 | Large, soft pink with a coral tone and darker veining towards the centre | Compact and dense. Pots, hanging baskets and mixed plantings |
| Ingrid F1 | Large, apricot to powder pink | Compact and dense. Pots, hanging baskets and borders |
| White Double F1 | Double and white, almost rose-shaped | Spreading. Pots, hanging baskets and larger plantings |
| Avalanche F1 | Large, white and trumpet-shaped | Strongly trailing. Hanging baskets, pots and larger areas |
| Angelica F1 | Large, white and trumpet-shaped with a paler centre | Also works in small pots and hanging baskets |
If the plant is meant to trail, choose Avalanche F1. If it is meant to grow dense in a pot, choose Yvette or Ingrid. White Double F1 needs the most deadheading, because double and large-flowered petunias seldom drop their spent flowers on their own.
Timeline from sowing to flowering
Count backwards from the day you can plant out. According to the growing guides from the seed breeder PanAmerican Seed, it takes 9-11 weeks from sowing to a flowering plant for single varieties and 10-14 weeks for doubles, in a greenhouse. At home, with less light, it is wise to plan for the upper end of that range.
| When | What you do |
|---|---|
| Late February to mid-March | Sow indoors at 20-25°C. The seeds germinate in 1-3 weeks. |
| April, 4-5 weeks after sowing | Prick out into individual pots and lower the temperature to around 18°C. |
| Late April | Start feeding and pinch out the tips of the plants. |
| Mid-May | Start hardening off, about two weeks before planting out. |
| Late May to mid-June | Plant out once the risk of night frost has passed. |
| June to October | Flowering. Deadhead, feed every week and cut back straggly stems in July. |
Sow the seeds on the surface
Petunia seeds are as fine as dust and need light to germinate. For that reason they should never be covered with compost.
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Prepare: Fill a tray with seed compost, water it until it is moist all the way through and level the surface.
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Scatter: Tip the seeds into a folded piece of paper and tap them out thinly over the surface.
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Press down: Press the seeds lightly into the compost with the palm of your hand.
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Cover with a lid: A clear lid or cling film keeps the moisture in and lets the light through.
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Warmth: Put the tray somewhere light at 20-25°C. At 21°C most seeds germinate in 5-10 days. If it is cooler it can take up to three weeks.
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Water gently: Use a spray bottle or water from below, so the seeds are not washed down into the compost.
Cooler and lighter after germination
Remove the lid when most of the seeds have germinated and lower the temperature to 17-20°C. The seedlings now need 12-16 hours of light a day. In February and March a window seldom gives that much, so hang a grow light no more than 10 cm above the tops. There is more about lamps, compost and trays in our article on starting seeds indoors.
After 4-5 weeks, when the seedlings have two to four true leaves, prick them out into individual pots of potting compost. Lift each seedling by its leaves, not by the fragile stem. A few weeks before planting out, pinch off the top 2-3 centimetres. The plant then branches and becomes bushy instead of tall and sparse.
Petunia is a long-day plant, and long days speed up flowering. Sowing as early as January therefore mainly gives you more weeks of plants that have to be kept in good light indoors.
Mistakes that hold the seedlings back indoors
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The seeds are covered with compost: In the dark they germinate poorly or not at all.
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The tray dries out: The seeds lie on the surface and dry out quickly. Keep the lid on until most have germinated.
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Left in the warmth after germination: At 22-25°C without extra light the seedlings stretch and become weak.
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Planting out too early: A plant put outside in early May without hardening off can be damaged by sun and wind, and a single frosty night can kill it.
Planting out in pots, hanging baskets and borders
Harden off the plants over about two weeks. Start with a few hours in shade and shelter, and leave them out for longer and in more sun each day. Plant out once the risk of night frost has passed, which in most of the UK and northern Europe means from late May to mid-June, depending on where you live.
Choose a spot with at least five hours of direct sun a day. At 20 cm spacing, five plants fit in a one-metre window box. The compost should be rich and free-draining, and the pot must have holes in the bottom. There are more ideas for small spaces in the article on growing on a balcony.
Feeding and watering all summer
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Feeding: Petunias are hungry plants and use up the nutrients in a pot within a few weeks. Give liquid feed at least once a week throughout flowering. With Florea Fertilizer the dose is 2-3 tablespoons per litre of water twice a week.
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Watering: Keep the compost evenly moist, but do not let the pot stand in water. Hanging baskets and window boxes in sun dry out fast and often need water every day during hot weeks in July. Drought also makes the plant more vulnerable to aphids.
Yellow new leaves often mean iron deficiency
Petunias are among the plants that struggle to take up iron when the pH of the soil rises. According to e-GRO, a network of university researchers in greenhouse horticulture in the USA, iron deficiency can develop quickly once the pH of the potting compost goes above 6.2. Common causes are hard, lime-rich water and lime mixed into the compost.
| Symptom | Likely cause | What to do |
|---|---|---|
| The youngest leaves turn yellow between green veins, older leaves stay green | Iron deficiency, often caused by high pH | Feed with a fertiliser that contains iron, ideally as iron chelate, and water with rainwater |
| The oldest leaves turn yellow first | Nitrogen deficiency | Give liquid feed every week |
| Long, sparse stems with few flowers | Too little light | Move to full sun and cut back the stems |
After a treatment with iron, the new leaves should start to green up within 5-7 days. If nothing happens, the pH is probably still too high.
Deadhead and cut back in July
A spent flower that is left on the plant forms a seed capsule, and the nutrients then go into the seeds instead of into new buds. Pinch off the flower together with the green base behind the petals. If you only pull off the petals, the seed can still form. Go over the plants a couple of times a week, especially a double variety such as White Double F1.
In July many plants become long and sparse in the middle. Cut the longest stems back to about half their length and give an extra dose of liquid feed. Within a few weeks new side shoots with buds appear, and the plant then flowers until the first frosty night ends the season in September or October.
Author: Emma Vogiatzi
Fact-checked by Erik Hoekstra
Last updated 2026-10-19