September Gardening Advice

The onset of Autumn sadly marks the end of the gardening year for far too many gardeners, who view it as a time to tidy up and shut down before winter arrives. However, for those in the know, Autumn actually marks one of the busiest seasons in the garden and is the perfect time to get planting plans in place for the following year.

Our gardening advice for September and indeed the next few months will lighten your workload next spring and in many cases offer an easier start to establishing new plants in the garden.

In the flower garden

Border tidy – mixed borders can start to look unkempt this month as summer performing perennials start to wane.  The plants should be cut down as they die back, restoring order and tidiness to displays. Use a knife, secateurs or shears to cut the spent stems and foliage down to the crown (base of the plant).
A mulch of garden compost or similar will help to protect the dormant crowns from winter damage.  If the plant in question dies back fully, it can be fully covered with mulch. If it dies back to a basal rosette of leaves, these should be surrounded by mulch but left uncovered on top.
Any borderline hardy perennials such as penstemon, phygelius and salvia should be mulched, but their spent top growth should be kept in place until spring as extra winter protection for the crowns below.

Eking out summer displays – Summer hanging basket and patio containers will continue to run into mid-autumn if you keep up with deadheading, watering and feeding.  Even plants that are starting to straggle can be given another month or so of life by cutting them back and allowing new shoots to take over, but with our winter and spring bedding plants despatching now it may be best to empty containers and get them prepped ready for re-planting.

September sowing – Many flowering hardy annuals can be sown in beds and borders in September for earlier colour next year. They will establish roots and foliage this side of winter, waking up in early spring to put on a strong floral display in late spring/early summer.

Seeds should be sown in prepared, weed-free soil that has been raked level to a fine tilth. They can either be scattered (broadcast) over the area and raked in for an informal look, or the area can be divided into various patches and the seeds sown in drills for a more ordered look.

For more detailed advice on direct sowing see our guide.

If there is no space due to winter performing bedding displays, hardy annuals can be started off under cover and then hardened off for overwintering in a cold frame or unheated greenhouse for planting in out in spring.

Spring bulbs – Our selection of spring flowering bulbs start to dispatch through September, at the perfect time for planting for the best displays. We work very closely with our growers to ensure we offer the very best, top sized bulbs, which will provide you with a glorious spring show. All of the bulbs we offer have been trialled and tested, either on our own Suffolk trials ground or on those of our growers, to ensure we offer the best range for British gardens.

Bulbs are one of the best value investments for the garden, returning year on year with the absolute minimum of upkeep and care. Simply plant this autumn for years of bold spring colour in borders, containers, lawns, rockeries – these versatile garden additions will pretty much grow anywhere you plant them. For the best performance choose a sunny to partially shaded location in any moist but free-draining soil.

September planting – September is a perfect month for planting out new container grown perennials, trees and shrubs. Soils retain some of their summer warmth through the month but moisture levels are on the rise thanks to the autumn rain. This creates the perfect conditions for early root establishment and also reduces the level of watering needed during the critical early stages of establishment. Watering may be needed in prolonged dry spells next year, but winter wet will have done a large part of the settling in process for you.

Cold season colour – Our winter and spring bedding plants are dispatching now. These winter hardy plants have all been selected to guarantee winter and spring colour in borders, baskets and patio containers. Stunning on their own or mixed together, our pansies, violas, primroses, bellis daisies, wallflowers, and forget-me-nots all offer effortless colour for the colder months of the year.

Plant by variety, or mix together for a kaleidoscope of colour. All our bedding plants work perfectly with spring flowering bulbs too. As you plant your beds and borders add a bulb in between each plant for extra height and colour some spring.

On the Veg patch

Sowing – as in the flower garden, there is a range of hardy vegetables that can be sown this month for overwintering and early cropping next spring. If you are looking to avoid empty veg patches through winter, make sowings of the following in coming weeks: winter lettuce, corn salad, turnips, spring onion, broad beans, spinach, Oriental vegetables including Choi Sum and Pak Choi.

You can also make the last sowing of quick-cropping summer vegetables including radish and salad leaves. If autumn arrives fast in your area, these can be sown in containers and brought under cover when the first frosts threaten.

Spring cabbages – Spring cabbage seedlings sown in July and August should now be large enough to plant out. Soils should be improved ahead of planting by adding well-rotted manure or garden compost. Cabbages prefer a firm soil, so tread over the area and rake flat before planting. Set out in rows leaving 30-45cm between each plant and row.

Asparagus – September is a key month for establishing new asparagus crowns. They perform best in well drained fertile soils, rich in organic matter. Crowns should be set out in long trenches, 20cm deep and 30cm wide. Fill the bottom of the trench with a 7.5cm mounded layer of compost and soil.  Place the asparagus crown on top of the ridge, draping roots over the sides. Cover with another 7.5cm of soil, firm down and water. As growth commences next spring, gradually fill in the remainder of the trench as the spears develop.
Established plants should be cut down to the ground as soon as the foliage has browned. With easier access to the soil, the area should be thoroughly weeded and a good layer of mulch applied afterwards.

Onions, shallots and garlic – September is a great time to plant onions, shallots and garlic as the soil is still warm and the long days give high light levels. Overwintering your alliums will allow them to develop strong root systems to see them through the winter, ready to burst in to life in early spring. Our tried and tested varieties are guaranteed to produce fantastic yields of flavoursome and tender crops.

Onions, shallots and garlic should be set out in rows, in firm, free-draining soil in full sun. Soils should be improved ahead of planting but avoid setting them on a freshly manured soil. Leave 10cm between each bulb and 30cm between rows. The bulbs (or sets) should be planted with the tip of the bulb just showing above the soil surface.


In the greenhouse/on the windowsill

Overwintering – Towards the end of September start to bring prized tender plants under cover of the greenhouse to keep them frost free through winter. Many summer bedding plants can be overwintered this way, leading to bigger better displays the following year. Try it with fuchsias, begonias, geraniums, petunias and marguerites. Water sparingly until spring, but ensure good light levels by washing off shade paint and removing shade netting.

Early bulb colour For early indoor displays of your favourite spring flowering bulbs, pot up tulips, daffodils and hyacinths this month and leave them outside for six weeks or so.  Then bring into the greenhouse to encourage early growth. As soon as flower buds develop the pots can be brought into the house for spring colour in the middle of winter.

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