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What to Do in the Garden This September

Published on September 5th 2020

by AlanGardenMaster. All rights reserved

September flower border
September starts a new season for gardeners! There are bulbs to plant and pot up, plants to save for next year, propagating to be done and even a few seeds to sow.
This month, I've also got some tips for improving your lawn, hedge cutting and pruning. My wildlife tips are topical, and I haven't forgotten those indoor plants either. All in all, September is looking like another great month in the garden!
A close up of a red crocosmia flower

What to buy for your garden this September


  • Plant shady borders and areas under large shrubs with small-flowered Crocus, Scilla, Anemone blanda, snowdrops and English bluebells. Avoid planting Spanish Bluebells as they may hybridise with our own native bluebells.
English bluebell flowers
Native English bluebells
  • Try growing a few bulbs- other than the proverbial hyacinths- in pots for inside. It is much easier than you might imagine! Dwarf Iris aren’t often grown but are very easy to care for if they have good drainage. There are masses of dwarf Tulips and Daffodils to try! The easiest are Tulip 'Red Riding Hood' and ‘Pinocchio­’. For Daffodils, try ‘Tete a Tete’ or ‘Jet Fire’.
Pots filled with iris flowers on a table
Iris reticulata growing in pots
  • Remember to use bulb fibre rather than potting compost if the pots you use have no drainage holes. Ensure that the bulbs have plenty of roots and that you can feel the flower bud in the shoot protruding out of the bulb before you bring them into warmth.
Tulip Pinocchio flowers
Tulip Pinocchio is a good choice for pots
  • Pot up prepared Hyacinths to get them in flower for Christmas. Get them potted this month unless you are happy to have them in flower in January or later.
A wicker basket of hyacinths on a table next to a window
Hyacinth 'Lady Derby' in a wicker basket
  • Gladioli corms should be lifted, dried off and stored in a frost-free place. The small corms that form around the base are probably best discarded as they can take several years to reach flowering size. Hardy types can be left in the ground, but the majority will need lifting.
  • Lift and dry off begonia corms. Let the tops die back naturally so that the energy in the tops goes back into the corm.
Begonia flowers
Large flower begonias
  • Cut back and pot up any tender perennials worth keeping in the greenhouse. Fibrous rooted Begonias, Pelargonium, Fuchsia, Salvia and masses of other tender perennials can be saved if you have space!
Red begonias in a garden
Begonia semperflorens 'Super Olympian Red'
daffodil bulbs in a pot
'Paperwhite Daffodils in a pot

Pots and borders

  • Create a cottage garden effect by sowing easy to grow hardy annuals. Calendula and Love-In-A-Mist (Nigella) look good together. Cornflower, Larkspur and Clarkia will give some height to the middle and back of a border and are excellent cut flowers too! All can be sown directly into well-prepared soil where you want them to flower and don’t need to be raised in trays and transplanted. They are hardy enough to over-winter without frost protection and will give a good show next summer!
  • Take cuttings of Pelargonium, Fuchsia, Salvia, coleus and other tender plants.
  • Check cuttings of Fuchsia, Pelargonium and other tender perennials for roots. If well-rooted, pot them on into 9cm (3.5”) pots filled with good potting compost. If not, leave the potting until spring. There is still time to root more.
  • Cut back early flowering herbaceous perennials close to ground level unless they produce attractive seed heads. The seed heads and some dead stems and leaves can look enchanting with winter hoar frost on them.
Hoar frost on plants
Hoar frosted plants in winter
  • Lift, divide and replant herbaceous perennials that have finished flowering. Most perennials benefit from dividing every 2-3 years. Replant only the youngest bits and discard the old woody middles. Improve the soil with compost when planting and water well to get them re-established.
  • Replant pots and hanging baskets with autumn, winter and spring flowering plants. Plant closely as you will get less growth at this time of the year. Use fresh compost and Osmocote feed for the best results. Pop in some dwarf spring-flowering bulbs too!
A family planting up a hanging basket together
A family planting up a hanging basket together
  • Buy pot feet and put them under your outdoor containers so that the pots drain well in winter. Remove any saucers.
  • Save seeds from plants that you know will grow well next year. Label them, dry them and then bag them up and keep somewhere rodent-free, cool and dry.
A potting shed with seeds drying in paper bags
Seeds in paper bags in The Organic Garden's shed of Yeo Valley

Lawns, hedges, paths and drives

  • Scarify your lawn to remove old dead grass. Use a spring tine rake and put the old dead grass and moss onto the compost heap with some Garotta compost activator. Follow up with Westland Aftercut Autumn All In One.
scarifying a lawn with a rake
Scarifying a lawn with a rake to remove dead grass
  • Spike compacted areas of your lawn with a fork and brush in a turf dressing of premixed compost. This applies in particular to well-used areas. For larger areas, use a hollow tined aerator and brush in fine grit or coarse sand.
Hollow tine lawn aeration
Hollow tine lawn aeration
  • This is the best month for establishing new lawns. Sow new seed or turf; both after careful soil preparation. Don’t skimp on this, as it is the one chance to get it right!
  • Rejuvenate tired-looking lawns by over-seeding with a mix of fresh seed and proprietary lawn dressing compost. This is what professional greenkeepers regularly do. You can also use Westland Lawn Thickener (seed & feed).
  • Fast-growing hedges, such as Leylandii, may need trimming again and will look better throughout winter for it. Don’t leave this too late, as it might result in brown patches. Give evergreen hedges and topiary a final trim.
A man cutting a tall hedge
Cutting a tall conifer hedge
  • This is the perfect time to plant a new hedge or to place an order for bare-root plants to plant in winter.

Ponds and bog plants

  • Erect a net over your pond to prevent falling leaves from getting into the water, increasing the nutrient levels when they break down. They may also deprive the fish of oxygen as they decompose.
A large garden pond
Cover ponds with a net to catch falling leaves
  • Remove dead leaves from pond plants as they die back.

Trees, shrubs, roses and conifers

  • September is the beginning of the traditional autumn planting season and is the best time to plant hardy plants. The soil is moist and warm, and plants will soon get established, so get out your spades and get planting!
Two ladies planting a shrub
Planting hardy plants
  • Check roses regularly for black spot, mildew and rust fungal diseases. Remove and burn infected leaves and continue regular sprays of Roseclear Ultra or Multirose. Choose disease-resistant varieties to plant in the future.
  • Make sure that any Lavender plants are pruned now. Cut off faded flowers with about 2-3 cm of leaf shoot. Don’t cut back into old woody growth.
Lavender fields
Time to finish pruning Lavender

Wildlife and pets

  • Clean out nesting boxes and give your bird table a good scrub before the main bird feeding season gets underway. Jeyes disinfectant works well on bacterial and fungal diseases.
A robin nest box
A robin nest box
  • Start feeding birds again - if you ever stopped!
Find bird feed and more in the Chirpy bird food online shop:
  • Provide log piles in odd corners to act as wildlife refuges.
Birch log piles for wildlife
Log piles for wildlife at Le Manoir aux Quat’Saisons
  • Put up Lacewing, bee and Ladybird shelters to provide over-wintering refuges and encourage these predators to stay in your garden.
  • Install a frog and toad shelter. These are fantastic natural pest predators and real gardener's friends!
  • Cut a hedgehog door in your fence to let them in and out. They travel surprisingly long distances at night. Build or buy a hedgehog hibernation house.
A hedgehog in grass
A hedgehog in grass
  • Leave some seed heads and fruits on plants to provide food for winter.

The Indoor Garden

  • Reduce the frequency of watering as the days shorten.
  • Any houseplants, which are outside for the summer, should be moved back indoors now.
Ficus alii plant
Move indoor plants back inside now
  • Put humidity-loving house plants, such as ferns, Bromeliad and insectivorous plants, on a saucer filled with damp pebbles. Begin misting over the leaves of your plants- especially when your central heating comes back on.
A pitcher plant in a garden
Pitcher plants

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