What to sow and grow in September

Sow red hot pokers (Kniphofia) for stunning displays next summer
Image: Kniphofia uvaria from Thompson & Morgan

September might be peak harvest time, but there’s still plenty to sow and grow this month. For inspiration, check out our helpful 'what to do in the garden in September' guide.

Here's a handy list of what to sow in September, including all the flowers, fruits and vegetables to keep your garden ticking along:

Flowers to sow and grow

Start verbascum off in a cold frame in September
Image: Verbascum x hybrida 'Snow Maiden' from Thompson & Morgan

In the greenhouse/indoors

• Surface-sow euphorbia seeds now in trays indoors.
• Sow dierama seed now on the surface of moist compost. Keep in a cool greenhouse over winter.

In the cold frame / under cloches

• Sow Calendula officinalis‘Neon’ seeds in pots now and keep in a cold frame, for fruity colour from early summer next year.
• Sow viola hybrida 'Miniola Heart Purple' in a cold frame to plant out in the spring.
• Sow lupins ‘Band of Nobles Mixed’, Aquilegia x hybrida ‘McKana Giants Mixed’, aconitum and hollyhocks in a cold frame now.
• Sow eryngium ‘Blue Steel’ and Echinops ritro subsp. ruthenicus in pots and place in a cold frame this month to enjoy their silvery spiky foliage next year.
• Start Verbascum x hybrida ‘Snow Maiden’ seeds off outdoors now in pots in a cold frame.
• Sow perennial salvias into pots and trays outdoors and leave in a cold frame or unheated greenhouse through the winter.
• Sow red hot pokers into pots and trays outdoors for stunning flowers next summer.
• Sow Helenium puberulum 'Autumn Lollipop' in a cold frame to attract bees and butterflies into your garden next year.

Direct sow outdoors

• Sow Ammi majus ‘Graceland’ (Bishop's Weed) directly in the ground now where you'd like it to flower. Autumn sowing will produce bigger, more robust plants to grow.
• Sow hardy geraniums outdoors and leave them to over-winter.
• Direct sow hardy annuals, such as cornflowers, poached egg plant, annual poppies and larkspur 'T&M Improved', for bigger plants next year.
• Sprinkle California poppies into your borders for stunning colour late next spring.
• Direct sow Love-in-a-Mist (nigella) — it will over-winter quite happily and will self-seed prolifically!
• Sow delphinium seed this month for flowers next summer.

Plant outdoors

Plant sedum 'Sunsparkler Dream Dazzler' in September for late summer colour
Image: Sedum 'Sunsparkler Dream Dazzler' from Thompson & Morgan

• Fill gaps in your borders with autumn-flowering plants, such as sedum and Chrysanthemum carinatum 'Polar Star', to extend the colour to the end of the season.
• Plant hyacinth and amaryllis bulbs for forcing, to ensure a crowd of colourful blooms at Christmas. Keep them in a dark, cool place like a shed or garage and bring them indoors when the shoots are 5cm tall. Perfect for a homemade Christmas present!
• Plant spring-flowering bulbs, such as daffodils, crocus and hyacinths.
• Plant out any biennial plants sown earlier in the year. This includes foxgloves, wallflowers and pansy plants.
• Plant new perennials, trees and shrubs. Now is a good time as the soil is still warm and increasing rainfall should be on its way.

Herbs & vegetables to sow and grow

September's your last chance to sow summer radishes
Image: Radish 'French Breakfast 3' from Thompson & Morgan

In the cold frame/ greenhouse/ under cloches

• Direct sow spinach now and offer cloche protection as the weather cools. This will ensure harvests throughout autumn and winter.
• Sow spring cabbages, such as 'April' and 'Durham Early' into modules in the greenhouse.
• Sow pak choi ‘Green’ under cloches now for an autumn supply of baby salad leaves.

Direct sow outdoors

• Sow corn salad (lamb's lettuce) now — it’s a fully hardy crop which can be sown outdoors now for cropping throughout the autumn and winter.
• Sow green manure on empty beds now to help improve your soil structure and prevent weeds establishing over winter.
• Sow 'Hi Keeper' onions into a well-prepared seedbed — these are the best variety of onion for autumn sowing. Only thin your onion seedlings in the spring.
• Direct sow salad leaves now for quick crops.
• Try sowing the very hardy 'Perpetual' spinach outdoors this month for winter harvests later in the year.
• Sow winter-hardy spring onions, such as 'White Lisbon' and 'Performer' for crops next spring.
• Make your last direct sowing of summer radish ‘Rainbow Mixed’ this month for autumn cropping.
• Sow turnip seeds into well-prepared beds for small roots.
• Sow winter lettuce, such as 'Arctic King', directly into the ground now.

Plant outdoors

September is the time to get onion sets in the ground
Image: Onion 'Shakespeare' (Autumn Planting) from Thompson & Morgan

• Start planting garlic sets at the end of the month for cropping next year.
• Plant autumn onion sets this month.
• Plant out any spring cabbages, like ‘Advantage’, sown during the summer.

Keep one step ahead — what to order this month

Stock up on rhubarb crowns for planting in September
Image: Rhubarb 'Champagne' (Spring/Autumn Planting from Thompson & Morgan

• Order sweet pea seeds to sow in cold frames in October.
• Buy autumn onion sets, like 'Senshyu', for an early summer harvest next year.
• Order rhubarb crowns and asparagus crowns to plant next month.