September has been the hottest month on record, but as I now write (early October) there has been a change in the weather which has turned a lot cooler, with rain and quite cold nights.  By the time you read this if you haven’t already done so bring in tender plants and crops under cover.  Have some fleece handy to throw over tender plants in pots too large to bring inside and move them to a sheltered site.  
As late perennials finish flowering cut down the top growth, weed and fork between the plants. Cut late summer flowering clematis right down to soil level.  Plant new herbaceous perennials and dig up, divide and replant any that are overcrowded.  Plant lilies, ornamental onions and lily-of-the-valley for forcing.    Plant polyanthus, sweet William, wallflowers, foxgloves, forget-me-nots and Canterbury bells.  Mulch established plants with peat or leaf mould.  Penstemons are best left until the spring, when they can be cut back further. Lift and store dahlias, cannas and tuberous bedding begonias that have been hit by the first frosts. Take root cuttings of oriental Poppies.  Plant tulip bulbs this month to make a lovely spring display and it is not too late to put in your daffs.
Plant out bare rooted roses and pick up and burn any fallen leaves.  Heel in roses that cannot be planted straight away.  Make sure climbing roses are tied in.  Prune wisteria side shoots to 10-15cm from their base.
Get the soil ready for spring sowing; this is the last month to dig it over before winter sets in. Asparagus beds should be dressed with rotted manure and prepare new asparagus beds for planting up in the spring. Plenty of organic matter and grit will help to improve drainage to the level required by asparagus.
Beetroot and carrots should be lifted and prepared for the freezer. Celery and leeks require earthing up. Parsnips may need covering.  Spinach will continue to crop as it is thinned.
Stake Brussels sprout plants.  Protect cauliflower curds by bending the leaves over them.  Lift and store artichokes in sand.  Sow broad beans and early peas under cloches.
Plant onion sets and garlic.   Over-wintering onions currently in the ground should be protected with horticultural fleece by early March when fly starts to lay its eggs.  Adults are active between March – April and October – November.  
Start winter pruning of established, open-grown apple and pear trees (not cordons, espaliers, pyramids or fans) as soon as the leaves have fallen.  This is the month to plant Fruit trees.  You can if you wish spray trees with a suitable wash.  Do not prune plums, damsons, gages, apricots, nectarines, cherries.  These are best pruned from April to June.
Currants and Gooseberries should be planted, figs will need thinning and new Strawberry plants should have some manure spread between the rows.   
Rake the lawn with a wire toothed rake to remove dead grass if you have not already done so and spike to improve drainage.  Apply an autumn feed.