Sow seeds of biennials like: angelica, clary sage, anise and caraway in pots to keep in a cold frame or cold greenhouse over the winter. Seeds that require vernalization before they will germinate should be sown outdoors in pots or directly into the ground. These include: sweet cicely, aconite, primrose and sweet violet.
Finish collecting seeds heads for saving as they ripen.
Many perennial herbs may be divided in autumn for replanting in the border or for starting off as new plants in pots. For example you can dig up French tarragon and put it into a large pot and leave it in a cold greenhouse over winter for dividing into new plants in spring.
Now is the right time to take hardwood cuttings of fully mature wood from shrubs and trees suitable to be propagated by this method. These include: roses, blackcurrants and willow.
Clean your herb garden by cutting back dead top growth of hardy herbaceous perennials which do not need winter protection like: mint, lemon balm and pot marjoram. Also remove any annuals like: pot marigold, borage, summer savory, sweet marjoram and biennials that are in their second year of life such as: parsley and caraway, and put them into the compost.
Remove fallen leaves and also put them into the compost or make leaf mould. Clear any garden debris as all decaying material left lying on plants will encourage fungal diseases.
In early autumn give box hedges and formally clipped topiary a last trim. Make sure you do this well before the onset of frosts. Prune deciduous shrubs in late autumn to early winter, when they lose their leaves. Common elder will benefit from a hard pruning at this time to encourage bushy new growth for the next season and to help retain and neat and controlled shape.
Prepare the soil
Autumn is the best time to prepare the soil for new plantings. Dig heavy soils and spread with manure to be broken down by winter frosts.
Herbs in containers
Bring in tender and half-hardy container-grown plants before frosts begin. Cut back excess top growth and give them a minimal amount of water.
Some of the herbs that will remain in the garden over the winter will need protection. Protect the crowns of French tarragon left in the ground and other garden-grown plans that are not fully frost-hardy, with agricultural fleece or a coat of straw or bracken.
To ensure the survival of these plants like: tarragon, tricolor sage or other less than hardy pants, dig up at least one root and pot them up then put them in a cool greenhouse over the winter.