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.

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.