Beginning of Autumn Gardeners Checklist: What to do in September

September marks a crucial transition in the gardening calendar as we move from summer's growth to the calm, cooler days of autumn. With the first frosts on the horizon, it’s the perfect time to prepare your garden for the colder months ahead. This month is ideal for assessing your garden’s needs. Whether you choose to cut back spent plants and tidy up borders or leave some areas untouched to support wildlife, the decision is yours. The days are still warm enough to promote ripening, but with shorter daylight hours and cooler nights, growth will soon begin to slow. Now is the time to plan and protect your garden for the season ahead!

This guide will cover essential tasks like planting overwintering crops, maintaining a steady supply of herbs, and incorporating sustainable practices to keep your garden thriving. Be sure to download our Monthly Gardening Checklist Template to help you stay organised!

Overwintering Herbs

As September arrives, it's time to start thinking about how to keep your herbs thriving through the colder months. By taking the right steps now, you can ensure a steady supply of fresh herbs throughout winter and help your garden bounce back in the spring.

Preparing Container Herbs For Winter

As the weather cools, adjust your care routine for container herbs. Reduce watering as they enter dormancy since they need much less moisture during this period. For tender herbs kept outside, position containers against a wall to shield them from rain and benefit from residual warmth. Wrap terracotta pots in sacking for extra insulation. If you move any herbs indoors, be careful not to overwater—keep the soil slightly damp to avoid mould.

Bringing Tender Herbs Indoors

For less hardy herbs like mint and French tarragon, consider bringing a small section of the plant indoors. This way, you can enjoy fresh herbs all winter long. Additionally, you can take cuttings from mature plants and propagate them indoors. Place these herbs in a sunny spot and regularly check for pests, pruning away any damaged or discoloured leaves. Your herbs will gradually adapt to the reduced light indoors. If some leaves wilt due to transplant shock, prune them and water them sparingly.

Pruning and Dividing Shrubby Herbs

Shrubby herbs such as sage, rosemary, and thyme benefit from light pruning before winter. This encourages healthy growth and prepares them for the coming season. Early autumn is also a great time to divide and replant clumps to rejuvenate these perennials. By taking these steps, you’ll not only ensure their survival over winter but also promote a robust comeback in the spring.

Plant Strawberries

Autumn is a great time to plant strawberries, especially if you opt for bare-root runners. These small, leafless roots might not look like much, but they’re ready to grow as soon as you plant them. Aim to get them in the ground before mid-September to give them time to establish and avoid cold, wet conditions that can hinder their growth.

Preparing and Planting

Traditionally, strawberries are planted in neat rows directly into the ground. If your soil isn’t ideal, raised beds can provide better drainage and growing conditions. Strawberries also thrive in containers, growing bags, or hanging baskets, making them perfect for small gardens or urban spaces. Before planting, enrich the soil with plenty of organic matter. Apply a general-purpose fertiliser high in potash to promote healthy growth. Space your strawberry runners 30-45cm apart, with rows 75cm apart, and gently press the soil around the roots. Water thoroughly and keep the soil consistently moist during the first few weeks to help the plants establish themselves.

Bare-root runners, often available in late summer to early autumn, are an eco-friendly choice with no plastic pots to dispose of. Plant them during this period to give them time to establish before the winter chill sets in. Avoid planting strawberries in winter, as they struggle in cold, waterlogged soil.

For those with limited space, strawberries do well in containers like pots, baskets, or window boxes. Choose a container at least 15cm wide and plant one strawberry per pot. Ensure the soil is moist but well-drained by using a compost mix with a layer of gravel or broken pottery at the bottom.

Caring for Your Strawberry Plants

Consistent watering is crucial, especially during dry spells or when the plants are young. Focus on watering at the base of the plant, avoiding the leaves and fruit to prevent diseases like grey mould. With the right care, your strawberry plants will reward you with a bountiful and delicious harvest.

Plant Onions

Autumn is the ideal time to plant overwintering onion sets, like Japanese onions. These hardy varieties are ready to harvest by July, providing an earlier crop than spring-planted onions. Autumn planting also helps bridge the ‘hungry gap’—that period when winter crops are finished but spring crops aren’t yet ready. You can even harvest some early as young shoots for fresh 'spring onions' in April.

Planting Your Onion Sets

Onions thrive in well-draining soil, so it’s crucial to prevent waterlogging during winter, which can cause the bulbs to rot. Raised beds are excellent for improving drainage. Before planting, loosen the soil with a digging fork or trowel, breaking up any large clumps. If your soil is heavy, mix in horticultural grit or well-rotted compost to enhance drainage.

Space your onion sets about 10cm apart in rows that are 20-30 cm apart. Make sure the tips are just above the soil surface. After planting, snip off the wispy ‘tail’ on each set to deter birds from pulling them out. Onions require minimal care once planted—water only if the soil is extremely dry in autumn. In spring, as the weather warms, increase watering to keep the soil from drying out. Keep weeds at bay by removing them by hand to avoid disturbing the onion bulbs.

Managing Common Issues

To prevent problems like white rot and stem eelworm, practice crop rotation and maintain good garden hygiene. If you spot orange pustules on the leaves, it’s likely rust, which usually doesn’t harm onions but can be an issue for leeks and garlic.

Top Overwintering Onion Varieties

• 'Senshyu Yellow': A classic favourite for overwintering
• 'Radar': Extremely hardy and perfect for harsh winter conditions
• 'Snowball': A mild-flavoured, white skinny variety.
• 'Electric': A reliable red onion that overwinters well.

Preserving Your Flower Garden

Drying flowers is a wonderful, eco-friendly way to capture the beauty of your garden and create stunning winter decor. These preserved blooms are perfect not only for display but also for handmade crafts, soaps, and more. And don’t limit yourself to just flowers—seedheads, foliage, and twigs can add a natural, whimsical touch to any arrangement.

How to Dry Flowers

For the best results, pick your flowers in the late morning when the leaves are dry. Choose blooms that are either in bud or midway through blooming—they’ll continue to open slightly as they dry, ensuring they stay fresh and avoid drooping. Flowers like Statice (Limonium Sinuatum) and Mophead Hydrangea (Hydrangea Macrophylla) are excellent choices for drying.

Start by gently removing the leaves and tying the stems into small bunches. Hang them upside down in a cool, dark, and well-ventilated space. This method helps the stems stay straight as they dry. For delicate seed heads or smaller flowers, you can dry them individually by threading them onto a string with a needle and suspending them between supports. This thoughtful process lets you enjoy the essence of summer even as the colder months set in.

Drying Seedheads

Harvest seed heads when they are fully mature but still intact. One favourite is Honesty (Lunaria Annua). Cut them on a dry day to prevent mould, then trim the stems and stack them in a warm, dry place. Alternatively, display them in a large vase. After a few weeks, the outer casings of the seedheads will be ready to peel back. Each honesty seed head has three layers: two protective outer layers and a stunning, silvery, paper-like layer in the middle. Gently remove the outer layers, harvest the seeds, and you’ll be left with beautiful, pearlescent seedheads—perfect for autumn bouquets or other decorations. 

Storing Your Saved Seeds

Proper seed storage is essential for next year’s planting. Make sure all seeds are thoroughly dried before placing them in labelled paper envelopes. Store them in a cool, dark place, away from light, heat, and frost. Berried seeds and seeds from hardy trees and shrubs can be sown into pots now and left outside, allowing the winter cold to trigger spring germination.

Start Composting for Next Year

As you tidy up your garden this September, put that garden waste to good use by starting a compost heap or bin. Autumn is the ideal time to begin composting, with falling leaves and garden clippings providing plenty of material to get started.

Choosing The Right Composting Method

If you don't have space for a traditional compost heap, consider using a compost bin. Compost bins are compact, making them perfect for smaller gardens. Place your compost pile or bin in a well-drained spot to encourage worms to help break down the contents. Worms thrive in the moist, dark environment of a compost heap, turning waste into nutrient-rich compost and liquid feed.

For a healthy compost, aim for a balanced mix of "green" and "brown" materials:

• Green materials: Vegetable peelings, fruit waste, tea bags, plant prunings, and grass clippings. These break down quickly, adding nitrogen and moisture.
• Brown materials: Cardboard egg boxes, scrunched-up paper, fallen leaves, and crushed eggshells. These decompose more slowly, adding essential carbon, fibre, and air pockets.
• Avoid adding meat, dairy, diseased plants, or perennial weeds like thistles and dandelions, as these can attract pests, create odours, and introduce unwanted seeds.

Building and Maintaining Your Compost Heap

To start your compost heap, layer dried plant material with fresh green matter. Ensure the pile has good air circulation and moisture, with a balanced mix of green and brown waste. Adding a few handfuls of soil will introduce beneficial microbes, and incorporating manure or a nitrogen fertiliser can speed up decomposition. Water the pile and cover it with polythene or tarpaulin to retain moisture and warmth, which accelerates the composting process. Turning the heap occasionally also helps it break down faster.

Your compost will be ready when you find a dark brown, almost black, soil-like layer at the bottom of your bin. It should have a spongy texture and be rich in nutrients. Spread this finished compost onto your flowerbeds to improve soil quality, retain moisture, suppress weeds, and reduce the need for chemical fertilisers and pesticides.

Transform your Lawn into an Ecosystem

As autumn approaches, your lawn can become a vibrant habitat for various creatures when managed with nature in mind. By skipping moss killers, weedkillers, and artificial fertilisers, you create a welcoming environment for mosses, lichens, autumn grasses, and late-blooming wildflowers like clovers and speedwells. These plants not only add beauty to your lawn during the autumn months but also provide essential nourishment for bees, hoverflies, and butterflies preparing for winter.

To encourage this natural diversity, consider mowing your lawn every two weeks instead of weekly as the weather cools. This allows wildflowers to flourish, providing late-season food for pollinators and transforming your lawn into a lively autumn ecosystem. Even worn paths and bare patches can serve a purpose, offering ideal nesting sites for solitary bees preparing for the colder months. Shorter grass attracts green woodpeckers, who feast on ants, and tawny mining bees, who create charming burrows before winter sets in.

By making a few simple adjustments to your lawn care routine this September, you can support a rich and diverse ecosystem right in your garden. It’s amazing how much life can thrive with just a few thoughtful changes as autumn unfolds!

Embrace September’s gardening opportunities

September is the perfect time to prepare your garden for the colder months ahead. From planting overwintering crops to maintaining your herb supply, there are plenty of ways to keep your garden thriving.

Incorporating sustainable practices like composting and creating wildlife-friendly lawns can significantly reduce your environmental impact. Small changes in your gardening routine can lead to a more eco-friendly and productive garden. Use this month to assess, plan, and implement these strategies, ensuring your garden flourishes in the seasons to come!