Plant spring-flowering bulbs such as tulips, daffodils, crocus, anemones, and hyacinths. Plant directly in the ground or in pots as a bulb lasagne.
After the first frost, lift tender bulbs and store them over the winter. Includes dahlias, tuberous begonias, calla lilies, gladioli, elephant ear, and canna lilies.
Plant onion sets for a head-start on next year's onion harvest. In the UK, it's very easy to find 'autumn-planting' onion varieties and they include Red Baron, Sturon, and Senshyu. In North America, the type of onion variety you can grow (short-day, intermediate-day, and long-day), and when to plant them, is based on your region.
Plant garlic cloves from the autumn equinox to the winter solstice. There are two main types of garlic and tips on how to plant, grow, and harvest them are over here.
Sow sweet pea seeds in early autumn. They'll overwinter well and give your earlier flowers next summer.
Some broad bean varieties grow best if sown in early autumn. Sow now in small pots to overwinter in the greenhouse, or direct in the garden if your winters are mild.
If you'd like to grow a wildflower meadow next year, prepare the area and sow seeds in early autumn. They'll begin growing and overwinter as small plants before bursting to life in early spring.
Grow a new lawn from seed. The best time to sow grass seed is early to mid-autumn when weeds are less competitive and rainfall more reliable.
Sow cover crop seeds on vegetable beds that will be empty over the winter. Also called green manures, plants like mustard, rye, and clover will keep weeds from sprouting up in the winter. In spring, you dig them in to enrich the soil.
Divide perennials such as daylilies, peonies, oriental poppies, and Siberian iris. If it's a perennial and blooms in spring or early-to-mid summer, you can divide the plant into several pieces to create plants for free.
Plant potted trees in autumn. It's the perfect time to plant fruit trees and deciduous ornamental trees but wait until early spring for evergreens.
Plant winter-hardy bedding plants such as heather, violas, primroses, and cyclamen. They provide a splash of color during the gray days ahead and grow well in containers and in the border.
Pot up strawberry runners. By now the runners will have formed their own roots and can be cut from the parent plant. Overwinter strawberry plants in a greenhouse or cold-frame to plant out in spring.
Propagate perennials such as frost-tender lavenders, tomatoes, physalis, verbena, lemon verbena, scented geraniums and other pelargoniums, and anything else that won't survive the winter outside. Overwintered inside, or a frost-free greenhouse, they'll ensure you have plants again the following spring.
Prune summer-fruiting raspberry canes. These types of raspberries only fruit on second-year wood, and after a cane produces fruit, it withers. Cut these dead-looking canes about an inch from the ground, leaving the best of this year's canes to grow on.
Tomatoes grown in greenhouses or in mild climates can produce fruit into autumn. To focus the plant's energy at ripening green fruit, remove all of the tomato flowers from late summer to early autumn.
Garden and soil
Empty compost bins and heaps. Use the finished compost to amend your garden beds or to use as mulch, and return uncomposted materials to the heap. Applied as a mulch, the finished compost will feed the soil over the winter and prepare it for spring crops. You can build an inexpensive compost pile using wood pallets with these instructions.
Clear garden beds and borders of weeds, and mulch the soil with compost, straw, or another mulch material. Mulching by laying a 1-3" thick layer of organic material on the ground protects the soil from erosion and stops new weeds from growing.
Begin collecting leaves to make leaf mulch. Gather leaves fallen from deciduous trees, and place them in a compost bin or other open container. By spring they'll have broken down to a compost that's low in nutrients but high in soil conditioning properties. It's also great for making your own seedling compost.
Test your soil's pH. If it's too acidic you can amend with lime; if it's too alkaline, you can begin amending with sulfur and/or compost.
To support local wildlife such as birds, bumblebees, and hedgehogs, leave some untidy places in the garden. Heaps of leaves under hedges, seed heads in place rather than cutting them down, and logs, sticks, and twigs piled together.
Birds such as pigeons may target your crops over the winter. Use safer netting and practices to ensure your cabbages, brussels sprouts, and purple sprouting broccoli are protected.
Perennial plants in containers and pots are far more exposed to winter temperatures than plants in the ground. To help them survive, move the containers into a greenhouse or place them against the sunniest side of your home, where it will be warmer.
Protect cold-tender plants in the garden or pots by wrapping the foliage/crown in horticultural fleece, bubblewrap, bracken, straw, and other materials. This is really important to help plants like bananas and tree ferns survive cold weather.
Clean tools, stores, and pots
Clean out the garden shed. Ensure that soft materials and seeds are safe from rodents.
Clean all garden tools of dirt, muck, and rust. One incredibly useful tool for cleaning garden tools is a Japanese rust eraser. I have the Niwaki brand but there are others available too.
Empty summer annuals from their pots, containers, and window boxes. Compost the plants, use the potting mix as a mulch, and rinse out the pots.
Clear out and thoroughly wash the greenhouse or polytunnel. If you do it now, your overwintering plants will have fewer pests, fungi, mold, and pathogens to contend with over the winter.
Clean rain barrels (water butts) of bottom muck. It washes in from your home, shed, or greenhouse's roof.
Plants sold as 'organic' or 'open-pollinated' can create seeds that will grow true to their type. You can save money by saving your own seeds, and it's easy to save everything from calendula flower seeds, poppies, tomato seeds, and much more. If I could recommend one book that has everything you need to know about seed saving, it's Back Garden Seed Saving by Sue Strickland.
Nearly all gardeners collect more seeds than they need. In fall, and before you buy new ones, organize your current seed collection, and swap or gift the ones you don't need. There are various charities that will take them, and seed swaps (both in-person and online).
If you'd like to introduce wild native plants into your garden, collect a few seeds from an autumn nature walk. It's kinder to grow your own 'wild foods' than to take it away from wildlife.
Support local wildlife
Place a net over garden ponds. It will stop leaves from falling in and affecting the water quality. Keep it off the ground and ensure it's pulled tight to avoid catching birds or other wildlife. Remove once all the trees have lost their leaves.
Thoroughly wash all bird feeders, birdbaths, and other wildlife feeders. Keep food topped up, and make sure that animals have access to liquid water -- break the ice each morning if need be.
Hang birdhouses in favorable positions. They can provide cover for wildlife in winter and nesting boxes in early spring.
If you're in Britain or Europe, create winter hibernation areas for hedgehogs. You can build or buy hedgehog houses or just leave areas of the garden untidy. They love a dry heap of leaves tucked under shrubs or hedges.
Grass slows down its growth in fall, eventually going dormant until spring. Cut the grass for the last time on a bright and dry day in mid-autumn.
If you'd like to reduce the moss in your lawn, or just revive it, scarify the grass with a leaf rake to remove the thatch.
Keep on harvesting crops. Pumpkins and squash when they're at the desired color and hollow-sounding if thumped. Leeks, root vegetables, greens, apples, and everything else. If you have a glut, you can learn to preserve it.
If your garden tap is fed by an underground tap that may freeze in winter, make sure to turn the water off at the source. Run the tap after to drain the line.
Store items undercover that will suffer or rust if kept out in the winter elements. This includes hoses, garden furniture, BBQs, wheelbarrows, plant supports, bamboo canes, and garden tools.
Bring houseplants that have been living outside back indoors.