What to Plant in September in South Africa — Your Spring Seed Sowing Guide
September is one of the most exciting months in the South African garden. The soil is warming, the days are lengthening, and the risk of frost is fading across most of the country. It's the moment every gardener waits for — the green light to sow.
Whether you're working with a sprawling garden bed, a small balcony, or a few pots on a sunny windowsill, September gives you a generous planting window. Here's exactly what to sow this month, and how to give your seeds the best possible start.
Why September Is the Sweet Spot for Spring Sowing
South Africa's spring arrives earlier than many gardeners expect. By early September, soil temperatures in most regions (Gauteng, the Western Cape, KwaZulu-Natal, and the Northern Cape) have risen enough to support germination for a wide range of flower and edible seeds.
Sowing in September means:
- Flowers by November — most annuals take 8–12 weeks from seed to bloom
- Edibles ready before the summer heat peaks — especially important for cool-season crops like peas
- A longer growing season — more blooms, more harvests, more joy
If you missed August, don't worry — our August planting guide covers what carries over, and September is arguably the better month for most flower seeds anyway.
Flower Seeds to Sow in September
Cosmos (Cosmos bipinnatus)
Cosmos is the quintessential South African spring flower — fast-growing, drought-tolerant, and breathtakingly beautiful in mixed borders. Sow directly into prepared beds or large containers. Thin to 30cm apart. Expect blooms in 8–10 weeks.
👉 Shop: Cosmos Seeds — Mixed Colours
Sunflowers (Helianthus annuus)
September is prime sunflower time. Sow directly where they'll grow — sunflowers dislike being transplanted. Choose a full-sun position and water deeply but infrequently. Our heirloom, non-GMO varieties produce tall, multi-headed plants that are as good for cutting as they are for wildlife.
👉 Shop: Sunflower Seeds — Heirloom Non-GMO
Zinnias (Zinnia elegans)
Zinnias are one of the easiest and most rewarding flowers to grow from seed. They germinate in just 5–7 days in warm soil and produce an abundance of bold, long-lasting blooms perfect for cutting. Sow directly after the last frost risk has passed — September is ideal for most SA regions.
👉 Shop: Variety Zinnia Seeds — Mixed Colours
Sweet Peas (Lathyrus odoratus)
Sweet peas are best sown in late August or early September in cooler regions (Highveld, Cape). They prefer cooler root temperatures, so mulch well and provide a trellis or support structure. The fragrance alone is worth every effort.
👉 Shop: Sweet Pea Seeds
Dahlias from Seed
Most gardeners grow dahlias from tubers, but growing from seed is deeply rewarding — and more affordable. Sow indoors in September and transplant once seedlings are established. You'll have blooms by late summer. Read our full guide: Dahlia Seeds vs Tubers — What Happens When You Grow Dahlias from Seed?
👉 Shop: Dahlia Seed
Queen Anne's Lace (Daucus carota)
This wildflower is a pollinator magnet and a stunning addition to any cutting garden. Sow directly in September — it needs light to germinate, so press seeds gently onto the soil surface without covering. Both our white and chocolate varieties are worth growing together for a dramatic contrast.
👉 Shop: White Queen Anne's Lace Seeds | Chocolate Queen Anne's Lace Seeds
Edible Seeds to Sow in September
Garden Peas
Peas are a cool-season crop — sow them early in September before the heat arrives. They grow quickly and can be harvested within 60–70 days. Provide a simple trellis and water consistently.
👉 Shop: Garden Pea Seeds
Peppadew (Sweet Piquanté Pepper)
Start peppadew seeds indoors in September for transplanting in October–November once temperatures are reliably warm. They need a long growing season, so getting them started now gives you a head start.
👉 Shop: Peppadew Seeds — Sweet Piquanté Pepper
Mixed Herbs
Basil, parsley, chives, and coriander all thrive when sown in spring. Start indoors or in a sheltered spot and transplant once established. Herbs are the fastest way to make your garden edible and useful.
👉 Shop: Mixed Herb Seeds
How to Prepare Your Soil for Spring Sowing
Good soil preparation is the difference between seeds that thrive and seeds that struggle. Before sowing:
- Loosen the top 15–20cm of soil with a fork or trowel
- Remove weeds — they compete aggressively with seedlings
- Add compost — a 5cm layer worked into the top soil dramatically improves germination rates
- Water the bed the day before sowing — moist (not wet) soil is ideal
- Sow at the correct depth — a general rule is to sow seeds at a depth of 2–3× their diameter
For a full step-by-step guide to getting started, read our Spring Seed Starting Guide for South African Gardeners.
Not Sure Where to Start? Try a Garden in a Box
If you're new to growing from seed or want a curated spring collection, our Garden in a Box — Seasonal Summer Blooms takes the guesswork out of spring planting. It includes a hand-selected mix of seeds suited to the South African spring season, with everything you need to get growing.
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What's Coming in October?
Once your September seeds are in the ground, October is the time to succession-sow — adding a second round of cosmos, zinnias, and sunflowers to extend your bloom season right through summer. We'll have a full October planting guide ready soon.
In the meantime, explore our Best Flowers to Grow from Seed in South Africa for more variety inspiration, and our Garden Planning for Beginners guide if you're just getting started.
Happy sowing. 🌱
Diamond Field Blooms seeds are heirloom, non-GMO, and packaged in biodegradable materials. Find out why that matters to us.