As we move gently into Autumn the garden visibly slows down and as gardeners we can relax and hopefully enjoy the glorious weather that September often serves up. Most herbaceous perennials and annuals have finished for the summer, if you keep cutting the sweet peas may still be flowering for a few weeks and roses maybe rewarding you with a second flush of flowers or seasonal display of hip - there is still plenty of late colour in the garden.
Late Summer & Early Autumn Colour
There are some late flowering perennials, climbers and shrubs which are in their prime in September and help keep the garden going. Dahlia put on a fantastic show and Sedum flowers on well in to the Autumn with the added benefit that it attracts pollinators – the nectar rich flowers are often completely covered with feasting butterflies and bees.
Roses will often flower until the first frost, and those with a shorter flowering season often make up for it with a display of large colourful hips. Late summer and early autumn is also prime Hydrangea time with flamboyant flower heads which continue to look good as they dry towards winter.
By September Lavender has stopped flowering but the spent flowers remain on the plant – pruning now helps to keep it in a nice compact shape and encourages the plant to shoot preventing woody centres. Aim for light trim removing all the spent flowering stalks to create a compact and neat shape for next year – dry the flowers in bowls around the house for a natural and fragrant fly repellent!
Last Chance To Prune Wisteria
Late August and early September is the last time to prune Wisteria. This prune is to tie in any growth required for the Arch, Gazebo or Pergola and to prune out excessive growth, or long whippy shoots which are not needed or too long.
Cut long shoots back to within half a dozen buds from the main framework to encourages flowering and ensure that your garden structure does not become overwhelmed by vigorous growth.
Cutting Back Perennials
During September many perennials will look tired, with browning leaves. Later, as frosts strike, some of the herbaceous perennials will collapse into brown heaps, but some garden plants keep their shape. Some plants look good as they fade, such as sedum and crocosmia where the flower heads and seed pods hold their own for weeks and look spectacular with a dusting Autumn dew or frost.
Some gardeners cut everything back, clearing out the borders, and others leave plants uncut to encourage wildlife and cultivate a less formal look. There is also a halfway house; cut back plants that look a mess, such as Hosta and Delphinium leaving in place those which still add to the border, at least for a while, which also spreads the work in the garden over the winter months.
There are no hard and fast rules about what to cut back once summer is over so take the opportunity to tidy as you will. Cutting back hard can help expose summer weeds which are sheltering under the plants so can help get the borders weed free for next season - a speedhoe will make sure you can weed without damaging planting
Deadhead to Prolong Flowering
It is still worth deadheading perennials and annuals, especially the late flowering ones. Depending on the weather, even annuals such as sweet peas may still flower and, to keep them going, continue to deadhead unless you want to collect the seed.
Start Planting Spring Bulbs
Autumn is the time for planting spring bulbs - Daffodils go in first during September with Tulips best left until October/ November. The correct planting depth is important - too shallow and bulbs will not flower well. An easy rule of thumb is to plant the bulb 3 to 4 times its own depth.
Late summer/early autumn is a good time to collect seed if you want to use it next year. Collect seed heads, carefully shaking or scraping out the small seeds and store in a packet in a dry place - a sealed tin is ideal. Store somewhere dry and cool and avoid the risk of moisture spoiling the seed – you can add a few grains of rice or any spare little packs of silica gel which come with some goods to keep everything nice and dry.
Protect Tender Plants
By late September, the risk of frost is not far away and it is a good time to consider which of the tender plants are worth saving to overwinter in a frost free place. For example, Pelargoniums survive well in a conservatory or a sunny porch, and look lovely for months as they continue to flower.
Raise the plants off the ground because the base can be very cold, especially sitting on concrete slabs. Raising the plants off the ground is warmer, and it allows air to circulate as the damp, stagnant air aids disease, especially grey mould, which can so often be a problem - overwintering tender plants gives you a head start the spring with a mature plant which should flower well.
If your lawn has developed bare patches, this is a good time to seed. The soil is warm and autumn tends to bring a little more rain which will help the seed to germinate and establish well before winter. If pigeons or birds are a problem in the garden, cover with net to stop them eating the seeds.
In the Kitchen Garden
September is the time to pick, freeze and store.
Onions and garlic will be ready either at the end of August or early September, depending on the weather. To harvest, choose a dry spell, bend over the top ease the bulbs out of the earth. Onions need to ‘cure’ on soil to dry out before bringing in for storage. If the weather is poor lay the onions out in the greenhouse or in a garage or shed – hang them up in netting or place on newspaper and make sure they are completely dry before .
Garlic is similar, wait till the top growth dries and turn brown usually in August/Sept. Store in a dry and light spot in the warmth rather than a cold area.
If you want to make onion or garlic strings when you harvest the bulb, keep as much of the top growth as possible to make into a plait. If there is not enough top growth, work in some raffia to help make a plait.
Harvest Main Crop Potatoes
Main crop potatoes can be harvested this month and to be stored somewhere dry and dark. Hessian sacks are ideal for storing potatoes - Potatoes can go green very quickly when exposed to light.
Tomatoes continue to need a lot of attention and it is important to water either daily or every other day depending on conditions and feed regularly at least twice weekly. As the month moves on towards October and the plants are naturally slowing down, reduce the amount of watering and feed. As the fruits ripen, the vines will need extra support and ties. Using soft raffia is good as it reduces damage to the tomato stems.
Sometimes it's difficult to get tomatoes to ripen late in the season – putting them in a paper bag with a ripe banana will help the process!
Still Time To Sow Herbs & Salad
In many parts of the country, this is the last chance to sow rocket and salad and if the weather is cool, cover with a cloche to encourage germination and growth.
This is a good time to replenish dried herbs, which lose their pungency after a period of storage. Ideal herbs for drying are Oregano, Sage, Mint and also, Thyme and Rosemary, although as hardy perennials, you can pick them all year round.
With the tender Herbs Basil, Coriander, dill & Mint, it is best to pot them up later in the month and bring in under glass ahead of any autumn chill.