Collect rainwater and five other gardening tasks to do now for a colourful display next Spring

This week: plant wallflowers now for a colourful spring display, test an apple and invest in new trees

To plant now

Biennials are one of the most useful and beautiful group of plants you can grow. The cast includes foxgloves, sweet Williams, sweet rocket, forget-me-nots and wallflowers; the latter pair fantastically well with tulips and alliums.

In an ideal world, we would have grown plants from seed months ago. However, life is seldom ideal so, if you haven’t had time to sow, buy young plants (or bare-roots in the case of wallflowers) from the garden centre and plant now to give them enough time to put down roots before winter.

Before planting, sprinkle a handful of Growmore per sq m to give them the best start.

Soil care

Summer-flowering annuals have been working tirelessly and some are showing signs of fatigue (I sympathise); as you start to clear and compost bedding plants, also think about your soil’s health. Bare earth is soon invaded by annual weeds and can lead to erosion if you don’t cover it.

Where soil is exposed, either replant or mulch with a 5-10cm layer of well-rotted compost or manure to improve fertility and soil structure. Mulching is a good workout and will improve the health of your plants tremendously. Before you mulch, make sure that the soil is moist (eg after rainfall) to lock that moisture in.

Catch the rain

Harvesting rainwater is a habit that we all need to adopt as the climate changes. Most rainwater falls September-April when we don’t need to use it, but capturing as much as we can stands us in good stead for summer.

This weekend, I suggest you check your gutters and clear them of debris and make sure that your downpipes are free-flowing. Where there is potential to capture rainwater, invest in a water butt or two, or three. Make sure that they come with lids to prevent problems with mosquitoes in summer.

Rainwater is great for watering orchids and indoor ferns throughout the year.

Apple picking

Depending on where you are in the country, September and October are prime months for apples. Fruit is ready to pick when:

1) There are a number of windfalls on the ground.

2) When you gently cup a fruit in the palm of your hand, lift and twist, it comes away easily.

3) Seeds inside the fruit are brown, not white. Finally, the taste test – take a big bite from an apple, and if it’s sweet then sugar levels are high and fruit can be picked.

Two projects to plan

Plant trees and shrubs

Autumn can be a wonderful time to plant trees and shrubs: the soil is still warm, which helps roots grow, and rainfall is more frequent (usually). Garden centres will be well stocked for autumn planting with a good range of woody plants. Although autumnal weather is beneficial for planting shrubs, we can still get caught out by prolonged dry spells. If you’ve treated yourself to new trees and shrubs, keep an eye on the amount of rainfall we get and supplement with, say, one watering can, twice a week, to ensure that new plants get their roots down while conditions are good. I make a small crater around the roots which helps to pool the water where it’s needed in those early stages.

Remove greenhouse shade

Without wishing to be the harbinger of doom, the reality is that sunlight is diminishing in intensity at this time of year and thus the growth rate of plants is slowing – particularly in greenhouses. If you applied shading to avoid scorching during the height of summer, it’s now time to remove it to make the most of the natural light still available to us. Use a soft brush and warm, soapy water to remove the paint and give the glass a good clean. The inside can have a good going-over when tomatoes, cucumbers and peppers have had their day in a month or so’s time.

Tom Brown is head gardener at West Dean Gardens, West Sussex. Follow him on Twitter @HeadGardenerTom; and on Instagram @tombrowngardener