When to Sow Nasturtium Seeds (UK Growing Guide)

Knowing when to sow nasturtium seeds makes a huge difference to how well your plants grow and how long they flower. Nasturtiums are fast-growing, easy annuals, but they are frost tender, so timing is important. Sow them too early and they may fail; sow them at the right time and they’ll reward you with months of colour and edible leaves and flowers.

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This guide explains exactly when to sow nasturtium seeds in the UK, whether indoors or outdoors, and how sowing time affects growth and flowering.

Best Time to Sow Nasturtium Seeds

In the UK, nasturtium seeds are best sown in spring, once temperatures begin to rise.

Recommended sowing times:

• Indoors: March to April
• Outdoors: April to May
• Flowering: June to October

Nasturtiums will not tolerate frost, so outdoor sowing should only happen once the risk of frost has passed.

When to Sow Nasturtium Seeds Indoors

Sowing nasturtiums indoors gives plants a head start and often leads to earlier flowering.

Best time for indoor sowing:

• Mid-March to April

Why sow indoors?

• Earlier flowers
• Protection from cold and slugs
• Better germination in controlled temperatures

Seeds should be sown individually in pots, as nasturtiums dislike having their roots disturbed. Keep seedlings in a bright, frost-free place and harden them off gradually before planting outside.

When to Sow Nasturtium Seeds Outdoors

Direct sowing is the easiest and most common method.

Best time to sow outdoors:

• Late April to May
• After the last frost
• When the soil feels warm

Cold or waterlogged soil can cause seeds to rot or delay germination, so waiting for warmer conditions is essential.

Can You Sow Nasturtium Seeds Too Early?

Yes, and it’s one of the most common mistakes gardeners make.

Sowing too early can lead to:

• Poor or failed germination
• Seed rot in cold soil
• Frost-damaged seedlings
• Slow, weak growth

Nasturtiums grow quickly once conditions are right, so there is little benefit to sowing early.

Sowing Nasturtium Seeds in Pots and Containers

Nasturtiums grow very well in pots, hanging baskets, and containers.

Best time to sow in pots:

• Indoors from March
• Outdoors from late April

Containers warm up faster than garden soil, which helps seeds germinate more reliably once temperatures rise.

Does Soil Temperature Matter?

Yes. Nasturtium seeds germinate best when soil temperatures are consistently warm.

• Cold soil slows or stops germination
• Warm soil encourages fast, even growth

If you’re unsure, wait an extra week rather than rushing sowing.

Can You Sow Nasturtiums in Summer?

Yes. Nasturtiums are very forgiving.

• Seeds sown in June will still flower
• Growth is rapid in warm weather
• Late sowings extend flowering into autumn

Staggered sowing can help maintain colour throughout the season.

Do Nasturtiums Self-Seed?

Yes. If flowers are left to set seed:

• Seeds drop naturally
• New plants may appear the following year

Self-seeded nasturtiums usually germinate later in spring, once soil temperatures are suitable.

Regional Differences in the UK

Sowing times can vary slightly depending on location.

• Southern UK: Outdoor sowing often possible from mid to late April
• Northern UK & Scotland: Late April to May is safer

Always consider local frost risk rather than relying solely on calendar dates.

Final Thoughts: When to Sow Nasturtium Seeds

In the UK, the best time to sow nasturtium seeds is March to April indoors or April to May outdoors, once frost risk has passed and the soil has warmed. Waiting for the right conditions leads to stronger plants, better flowering, and fewer problems.

Easy, colourful, and fast-growing, nasturtiums are a perfect reward for patient spring sowing.