September gardening guide: what to do in your garden this September
September is the start of autumn, and we can see the garden slowing down, but there is plenty of late colour in the garden - with late-flowering perennials, climbers and shrubs to keep the garden going.
Some herbaceous perennials and annuals would have finished for the summer, while others, such as roses, sweet peas, may keep on flowering. What exactly is flowering when will depend on the conditions in the spring and summer before.
Dahlia put on a fantastic late show, and Sedum flowers reliably late and attracts butterflies and pollinators. Roses will often flower until the first frost, and R. rugosa makes up for its shorter flowering season because of its beautiful and fragrant blooms followed by large colourful hips.
Late summer/early autumn is also Hydrangea time, with its wonderful fading flower heads that look good on the plant over winter.
September gardening guide: Planting
It’s time to think about Spring bulbs
Autumn is the time for planting spring bulbs. Daffodils need to go in first in September, and Tulips are best left until October/ November.
The correct planting depth is crucial to keep them flowering - too shallow, and they will not flower after one year. An easy rule of thumb is to plant the bulb preferably t to 4 times its own depth. There are some brilliant spring bulb combinations, and it is difficult to resist the bulb catalogues at this time of year.
There’s still time to sow herbs and salad
In many parts of the county, 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.
With the tender Herbs Basil, Coriander, Dill & Mint, it is best to pot them up later in the month and bring them in under glass ahead of any autumn chill.
Late summer/early Autumn is a good time to collect seed if you want to use it the following year. Collect seed heads, carefully shaking or scraping out the small seeds and store them in a packet in a dry place - a sealed tin is useful.
Moisture is the very worst thing for seeds that need to be stored dry and cool, such as in the garage or in a fridge. A small amount of milk powder can help to keep the moisture at bay.
Many seeds are easy to collect and germinate, such as Nasturtium, Viola, Rocket, the bean family. It is worth a try, given the cost of seeds.
September gardening guide: Care and maintenance
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 framework and to prune out excessive growth or long whippy shoots which are not needed or too long.
The long shoots can be cut back to within half a dozen buds from the main framework. Pruning wisteria twice a year will make it flower, and some years it may even produce a second show of small flowers in August.
Pruning lavender does help to give it a compact shape - but bear in mind that some lavender flowers early in the year while others are still flowering in September.
Whenever your lavender flowers, they should be pruned lightly into a tidy shape for next year when the flowers are spent. It is best not to cut into the woody stems because they will not readily regenerate. Just a light prune will do.
Deadhead to prolong flowering
It is still worth deadheading perennials and annuals, especially the late flowering ones. Depending on the summer, even annuals such as sweet peas may still be flowering. Continue to deadhead to keep them going unless you want to collect the seed.
Take care of tomatoes
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. When exactly to do this will depends on where the tomatoes are being grown.
If the plants are still growing, they will continue to produce leaves, and it is important to continue to thin these down to encourage the fruit to ripen. 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.
Overwinter and protect tender plants
By late September, the risk of frost is just around the corner. This is a good time to consider which 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 will look lovely for months as they continue to flower. Fuchsias and Pelargoniums can be put under glass others such as Petunias, Marguerite’s, Diascias, Osteopermums are ready for taking cuttings.
If overwintering plants in a greenhouse, it is a good idea to raise the plants off the ground because it can be cold - particularly if slabs have been laid as a greenhouse base.
Raising the plants off the ground also allows the air to circulate as damp, stagnant air aids disease, especially grey mould, which can often be a problem when overwintering plants. If you can overwinter the tender plants, it saves money for next year, and you can start the spring with a mature plant that should flower well.
September gardening guide: Harvesting
The vegetable plot is usually full with many crops ready for harvesting, and September is time to pick, freeze and store. Indeed, it’s difficult to avoid a glut of something or the other this time of year.
The main crop of potatoes can be harvested this month and stored somewhere dry and dark. Potatoes can go green very quickly when exposed to light - even if left in a greenhouse for 24 hours, they will turn green. To prevent this, you need to exclude light.
Potatoes also need to be dry. If they are wet when you dig them up, put them somewhere to dry off but quickly, as soon as they are dry, take them out of the light and put them in sacks, somewhere dry and dark.
Hessian sacks are ideal for storing potatoes. Hessian is good because it is a natural fibre, but you can use other materials - just avoid plastic or polythene, which will tend to trap moisture.
All the beans should be ready - creating a glut. Fortunately, all the beans family, French, broad, runners, and peas freeze really well. For best results, start by blanching in boiling water for 2 mins, then plunging into a bowl of iced water. Dry thoroughly and then freeze.
Courgettes are more difficult as they don’t really freeze very well.
Onions will be ready either at the end of August or early September, depending on the weather. To harvest, bend over the top growth (if this hasn’t already happened naturally) and harvest during a dry spell by easing the bulbs out of the earth.
Onions need to rest on the soil to dry out before bringing indoors for storage. Some years, it’s difficult to find a dry spell to rest the onions outside. An alternative, if the weather is poor, is to lay the onions out in the greenhouse - drop the foliage down between the slats and rest the onions on the slats.
Onions can also be dried in a shed, placed in netting, or even on a newspaper in a conservatory. The onion bulbs must be completely dry before storing.
The same applies to garlic. 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, retain as much of the top growth as possible to make it into a plait. If there is not enough top growth, work in some raffia to help make a plait.
This is also a good time to replenish dried herbs, which lose their pungency after a period in storage. Ideal herbs for drying are Oregano, Sage, Mint and also if Thyme and Rosemary, although as hardy perennials, they can be picked all year round.
September gardening guide: Wildlife and pests
- Start feeding birds with fat balls and peanuts that will help them through the winter.
- Take down nest boxes and clean them with disinfectant before drying and putting them back up.
- Remember to leave some seed heads in your garden through the autumn as food for birds and other wildlife.
- Leave some leaf litter in the garden over the winter as cover for hibernating insects.
September gardening guide: Other garden tasks for September
Raise pots up on pot feet or bricks to prevent them from becoming waterlogged through the winter.
Finally, if your lawn has developed bare patches, this is a good time to seed. The soil is warm, and there should be plenty of rain through autumn, which will help the seed to germinate and get going. If pigeons or birds are a problem in the garden, cover the seeds with a net to stop them from being eaten.