How to grow annual flowers indoors

How to grow annual flowers from seed

Annual flowers are easy to grow from seed. We show you how.

A table displaying which months are best to sow, plant and harvest.
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
At its best
At its best

Plant is not at its best in January

Plant is not at its best in February

Plant is not at its best in March

Plant is not at its best in April

Plant is not at its best in May

Plant is at its best in June

Plant is at its best in July

Plant is at its best in August

Plant is not at its best in September

Plant is not at its best in October

Plant is not at its best in November

Plant is not at its best in December

To do
To do

Do not To do in January

Do not To do in February

Do To do in March

Do not To do in April

Do not To do in May

Do not To do in June

Do not To do in July

Do not To do in August

Do not To do in September

Do not To do in October

Do not To do in November

Do not To do in December

It’s easy to succeed with annual flowers. Follow your seed packet’s instructions but use your own judgement, too. Sowing temperatures vary between varieties; it’s roughly 18-24 degrees celsius for half-hardy annuals and 8-16 degrees celsius for hardy annuals. Use clean pots or trays, and start a new bag of multi-purpose compost. Hardy annuals often resent root disturbance so if you sow these indoors, sow them in cells that can then be transplanted without disturbing the rootball.

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You Will Need

  • Seeds
  • Seed tray or small pots
  • Multi-purpose, peat-free compost
  • Pea sticks
  • Secateurs

Step 1

Pricking out seedlings
Pricking out seedlings

When seedlings have their first true leaves, carefully prick them out into small individual pots or seed trays. Grow on in warmth for a few days, then move to a cooler windowsill.

Step 2

Zinnia flowers
Zinnia flowers

Direct sun is essential. Warmth-loving/delicate kinds are best on a patio; traditional hardy annuals thrive in the open garden. In a poor summer or cold location, salpiglossis, eustoma or large-flowered zinnias do best under glass or in a polytunnel.

Step 3

Compost
Compost

Annuals need fertile soil enriched with a little well-rotted compost and general fertiliser, such as blood, fish and bone. Use a multi-purpose compost for containers, and apply liquid tomato feed weekly from June onwards.

Step 4

Using pea sticks to support plants
Using pea sticks to support plants

Cut flowers need straight stems, so support is essential for taller species. Use pea sticks to provide support and tie plants to them where necessary.

Step 5

Deadheading spent flowers
Deadheading spent flowers

Unless you cut all annual flowers as they grow, you must remove spent blooms to prevent plants setting seed – otherwise they’ll stop flowering. Snip off fading flower-heads regularly to promote a fresh flush of buds.

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