Garden Jobs for September

September is a busy month. It’s back to school and time to gear up after the lazy days of August. Does the garden need a lot of attention this month? Depending on what you have in the garden, you can get away with just a few essentials.

aster in a somerset garden in September

Aster ‘Violet Queen’ great for autumn colour


If you didn’t find time to prune back your wisteria in August, it does need to be done this month. Wisteria is a vigorous grower and it can quickly get out of hand.  Long, whippy stems will have appeared over the summer and they need to be cut back to five or six leaves. Depending on the size of your wisteria, this can be a big job and you should get someone to give you a hand, especially if you are using a ladder.

Lavender can also be cut back now. Or it can be left until October, but it should be done before winter. Cut back to just above the start of this season’s growth.  Don’t cut into last season’s growth or you risk killing it. Similarly, evergreen hedging such as box, yew or privet can be given a final cut to create a crisp line for winter. It may grow a bit more, however, so leaving this job until October is more likely to leave you with sharp edges.

Place an order for your autumn bulbs this month but don’t plant them until you are a week or so into October. A late burst of warmth (it could happen!) can fool the bulbs into an early growth spurt that can be damaged over the winter. As long as the ground isn’t frozen, bulbs planted as late as December will still appear, although they will be a little late flowering in spring. Check out my Bulbs for Every Month of the Year blog post if you’re not sure what to order.

Deadhead those plants that are still flowering, especially roses. It’s a case of diminishing returns with deadheading as eventually there are too many spent flowers to cope with, but it’s worth persisting for as long as you can bear it

Rudbeckia in a Somerset garden in September

Rudbeckia ‘Goldsturm’ are great autumn flowers


In times past gardens were mercilessly cut back in autumn as part of an end of season tidy-up. This could leave a garden looking rather shorn and removed habitats for over-wintering wildlife.

These days we try to leave plants for as long as they are looking good. Not everything can stand up to winter-long scrutiny, though. Perennials such as geraniums collapse into a mildewy mess and might as well be cut back as soon as they stop flowering.

So take a look at your flower borders and cut back anything that is looking a bit blah. If you have planned for a long season of interest you should have a few autumn stalwarts such as ornamental grasses, Japanese anemones sedums and asters keep things going.

Japanese anemones in an autumn garden in September

Japanese anemones are always elegant in the September border


September is a good time to review the flower border with a view to dividing any perennials that are past their prime, or even removing anything that hasn’t worked. October is the ideal month for dividing plants or new planting as the soil is still warm and the fragile roots of new plants have a chance to make some growth before winter. If you plan now you can order what you want for October planting and schedule the time to do the work (or perhaps get someone else scheduled to do the work…).

If you are interested in keeping your lawn green and lush, September is a good time for an autumn lawn treatment. The thatch (dead bits) can be removed by dragging a rake through your lawn. This is vigorous exercise, especially if you have a large lawn. Then aerate the lawn by pushing a garden fork into the ground every 15cm. Don’t bother with the special lawn aerators with hollow tines as, in my experience, they get clogged after the first use. You can finish off by working in a special autumn lawn treatment top dressing, using a stiff broom.

Or your September planning could include thinking about enlarging your flower borders and shrinking the lawn. A mixed border of shrubs and perennials needs less annual maintenance hours than a lawn, and provides more flowers!

If you have a greenhouse or cold frame, now is a good time to clean it before you start off any seeds in October. Cleaning the pots and trays you will use for propagating is also important, to get rid of pests and diseases. Those pesky slugs will lay eggs in the autumn and it’s bad news if the baby slugs appear in one of your trays of tasty, tender seedlings.  Be careful that you don’t leave bags of compost open in your shed as that will make a cosy place for slug eggs to overwinter.