When to Plant Nasturtium Seeds (UK Guide)

Knowing when to plant nasturtium seeds is the key to getting strong, healthy plants and months of colourful flowers. Nasturtiums are fast-growing, frost-tender annuals that thrive when sown at the right time, but they can struggle if planted too early in cold soil.

This guide explains the best time to plant nasturtium seeds in the UK, whether you’re sowing indoors or outdoors, and how timing affects growth and flowering.

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Best Time to Plant Nasturtium Seeds

In the UK, nasturtium seeds are planted in spring, once the worst of the cold weather has passed.

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

Nasturtiums dislike frost, so seeds should never be sown outside until there is no risk of frost.

Planting Nasturtium Seeds Indoors

Starting nasturtiums indoors gives plants a head start and earlier flowers.

When to sow indoors:

• Mid-March to April

Why sow indoors?

• Earlier flowering
• Better control of temperature
• Protection from slugs at seedling stage

Seeds should be sown individually in pots, as nasturtiums dislike root disturbance. Plants must be hardened off before being planted outside.

When to Plant Nasturtium Seeds Outdoors

Direct sowing is simple and works very well once the soil has warmed.

Best time to sow outdoors:

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

Cold, wet soil can cause seeds to rot or germinate poorly, so patience pays off.

Can You Plant Nasturtium Seeds Too Early?

Yes. Planting too early is a common mistake.

Problems caused by early sowing include:

• Poor germination
• Seed rot in cold soil
• Frost damage to seedlings
• Slow, weak growth

It is always better to wait for warmer conditions than rush nasturtium seeds into the ground.

Planting Nasturtium Seeds in Pots

Nasturtiums are excellent for containers.

When to plant in pots:

• Indoors from March
• Outdoors from late April

Pots warm up faster than soil, so container-grown nasturtiums often establish more quickly once outside.

Do Nasturtiums Self-Seed?

Yes. If flowers are left to set seed:

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

Self-seeded nasturtiums often germinate later, once the soil warms naturally.

What Happens If You Plant Nasturtiums Late?

Late planting is rarely a problem.

• Seeds planted in June will still flower
• Plants grow quickly in warm weather
• Later sowings may flower slightly later but remain healthy

Nasturtiums are forgiving and ideal for staggered sowing.

Final Thoughts: When to Plant Nasturtium Seeds

In the UK, the best time to plant nasturtium seeds is March to April indoors or April to May outdoors, once frost risk has passed. Waiting for warmer conditions results in stronger plants, better flowering, and fewer problems.

Easy to grow, quick to establish, and full of colour, nasturtiums reward patience far more than early sowing.