September, north of the equator

September is the most underrated month of the year. The soil is still warm, the rain has usually returned, and anything planted now roots into ground that is working rather than into the cold mud of spring. It is the best planting month there is, and it is also the last comfortable month before the light goes.

In the garden

Plant bulbs. Daffodils go in first, ideally early in the month, at three times the height of the bulb, which is deeper than almost anyone plants them. Hyacinths and the smaller spring bulbs follow. Tulips can wait, and are better for waiting, because cold soil holds back the fungus that causes tulip fire.

Sow hardy annuals where they are to flower. Calendula, cornflower, larkspur, love in a mist and poppies all sow now while the soil is moist and warm, and they flower earlier and larger next year than anything sown in spring. Sweet peas can be sown too, under a cloche or in a cold frame, and they make far better plants than a January sowing does.

Plant shrubs and perennials. Hydrangeas, hostas, ferns, jasmine and boxwood all establish beautifully in warm damp soil, and dividing overgrown clumps of hosta or other perennials is easiest now that the top growth is dying back and the crowns can be seen. Plant strawberry runners for next summer’s crop, and lift and store the last of the maincrop potatoes before the slugs find them.

In the house

Bring everything back indoors before the first cold night, and inspect each plant properly first. Look under the rim, into the compost and along the undersides of the leaves. A slug or a vine weevil grub brought inside in September has six months of warmth and no predators, and by March you will have lost a plant to it.

Lengthen the watering interval as the light drops. The change is quicker this month than last, and it follows day length rather than the weather, so a warm dull week still means less water than a cool bright one.

Stop feeding the plants that rest, and drop the others to monthly. Move everything closer to the window. The light that was too strong in July is exactly right now, and by November it will not be enough.

What not to do yet

Do not repot, because roots that are slowing down cannot fill fresh compost before winter. Do not cut houseplants back hard, which only makes work for a plant that is about to stop growing. And do not plant tulips yet, however tempting the packet in the shop looks in the first week of the month.