September tasks in the garden

Grow Your Own

• Keep picking crops of courgettes, runner beans, French beans, and start to pick sweetcorn (ripe kernels contain milky liquid, not clear).
• You can continue to crop Runner & French beans if you give them some food & water to keep them going. 
• Remove spent raspberry canes from summer-fruiting varieties and tie in the strong new growths. Pick autumn-fruiting varieties to keep them cropping.
• Pot up some mint & parsley for the kitchen windowsill.
• Garlic bulbs can start to be planted from the end of this month for harvesting next year.
• Take hardwood cuttings from currants & gooseberries if you want to increase your stocks.
• Lift & dry any onions that are still in the ground & store them in a cool, dry, frost free area.
• If you are going to store your pumpkins, marrows or squashes, leave them on the plant to mature for as long as possible before risk of frost. If you place them in a sunny place it will help to ripen them too.
• Give grape bunches sun - Ensure that bunches of grapes get enough sun to ripen. Remove some foliage from above them. Prune long tendrils back to a couple of ‘buds'. But stay at least ten centimetres away from bunches of grapes, since pruned stems can easily dry out that far back.
• Sow winter lettuce direct into the ground or in modules for planting out in a few weeks.
• Sow Oriental greens and spinach.
• Onion sets & spring cabbage to be overwintered can be planted now.
• Strawberry plants can still be established before winter arrives.
• Ripen remaining tomatoes indoors from the end of the month.
• Time to harvest maincrop potatoes which can then be stored in a dry place in the dark.
• Put greasebands on fruit trees.

Planting & Sowing

• Take cuttings of your favourite tender perennials to overwinter under cover e.g. fuchsias & pelargoniums.
• Collect seeds from perennials & hardy annuals & sow - such as Nigella (Love in the mist), Calendula (marigolds) and Limanthes (poached egg plant) for flowering next year plus spring flowering biennials such as Papaver nudicaule (Iceland poppies) & Digitalis (foxgloves).
• Plant perennials now for instant autumn colour - It is the ideal time of year as the soil is still warm and rain should help the plants to establish before winter sets in. If you plant perennials now (pot-grown perennials can be planted all year round) you need to know how they are going to develop in order to plant them the right distance apart. Soil, position, moisture and sun all have a big impact. A rule of thumb:
  • Plant low perennials approx 20 to 25 centimetres apart. (Approx 11 plants per m2 is the spacing often used for that group).
  • Plant medium-sized plants approx 35 to 40 cm apart.
  • For tall varieties it mainly depends on the habit. If they extend widely or produce a lot of overhanging foliage, then its best to give them at least a square metre each.
• Buy and plant spring-flowering bulbs such as narcissi, anemones and crocus; tulips can be planted now too but are better left a bit longer but planted before December.
• Buy cyclamen as plants and establish in groups; corms can be less successful as they have sometimes dried out too much.

Pruning

• Prune oleander - It is best to prune oleanders (Nerium oleander) vigorously when they go into winter storage. The benefit is that a lot of pathogens are removed.
• Spring & early summer flowering shrubs & trees such as forsythia’s & cherries will already have set their buds & should not be pruned now or you will have few flowers next year. Some selective pruning of long shoots can be carried out if plants need controlling.
• Shrubby honeysuckles, such as the evergreen L. nitida ‘Baggesen’s Gold’ can still be pruned now. Deciduous honeysuckles can be pruned after flowering which encourages them to produce more flowering side shoots. If yours has grown out of control, some of the main stems can be removed or for more drastic measures the plant will respond to a severe cutting back to about 30cm (12") with the loss of flowers for a few years.
• It is time for a final autumn trim for evergreen hedges & topiary.
• Prune late-summer flowering shrubs.

Maintenance

• Replant peonies - Peonies only start to flower profusely when they have spent three to four years in the same spot.
  • If they have access to sufficient nutrition, they will then flower lavishly there for many years, but there will come a time when the flowering diminishes.
  • The plants should then be dug up in September.
  • Divide the roots and use only the outside parts with multiple buds (shoots) for replanting. Plant in nutrient-rich, slightly moist soil and in a sunny spot.
  • Plant the parts so that they are just a few centimetres below the surface of the soil.
• Overwinter fuchsias - Give the plants lime-rich/nitrogen-poor fertiliser one more time this month. Give the plants less water two weeks before they go to their winter location. Then prune vigorously. Leave some twenty centimetres on the branches and also remove all the foliage. They can then go to their winter location (a cool room where the temperature needs to be approx 5 °C. Foliage will form again in the light. Water as required and check regularly for pests and diseases.
• To ensure that next year's buds develop well, keep your Camellias and Rhododendrons well watered at this time of year.
• (Re) plant conifers - September is an excellent month for planting conifers. They can then establish good roots before winter and will not suffer any problems with their ‘breathing' and water supply. The same applies to other evergreen varieties which are supplied with a rootball. Scale leaf conifers like Thuja, Chamaecyparis, × Cupressocyparis leylandii generally give fewer problems than needle conifers (Picea, Pinus, Abies), which sometimes have an anchored tap root which makes them harder to replant. (You don't need to worry about this if you are buying new plants from a nursery as the grower will ensure a compact rootball).
• Divide herbaceous perennials- After around three to four years perennials need to be dug up and divided in order to remain youthful and continue to flower profusely. With varieties which flower very early in the year and are starting to show signs of ageing, this is a good month to do this. Then they will have plenty of time to recover before the flowering period.
• Depending on which part of the country you live it may be time to bring in tender plants & house plants that have been outdoors for the summer. Keep a check on night time temperatures.
• Continue deadheading your Dahlias to get the most out of them before the first frosts.
• Treat perennial weeds such as dandelions & bindweed with a weedkiller containing glyphosphate which will kill the root.
• Watch out for early signs of powdery mildew which likes dry, shady areas or areas with poor air circulation. Pick off and destroy any infected leaves.
• Tree replanting - If you want to replant a tree, a good rule of thumb is that the diameter of the rootball must be ten times the diameter of the trunk.
• Do not feed your plants any more now. They need to prepare for winter.
• Use nematodes, whilst the soil is still warm enough, for organic control of vine weevil grubs.

Lawn Care

• Give meadows a final cut to a height of 7.5cm (3").
• Begin autumn lawn maintenance by scarifying, aerating and feeding.
• Prepare areas for reseeding and allow the soil to settle before sowing.
• Lay turf & keep watering if the weather is dry, until established.
• Reduce mowing of established lawns and raise the cutting height.

Pond Care

• Thin out submerged oxygenators if necessary.
• Net ponds to prepare for autumn leaf fall.
• Continue removing blanketweed and duckweed as necessary.