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Oak Leaf Gardening Monthly Cuttings
Newsletter 48 - May 2015
What to do now

Ornamental plants

  • Finish off sowing hardy annuals early this month. Continue to sow biennials such as honesty, foxgloves, stocks and wallflowers.
  • Keep on top of the pricking out, pinching out and potting on of seedlings.
  • Harden off and plant bedding and tender plants (leave towards the end of the month in cooler climates) including containers and hanging baskets.
  • Plant out summer bulbs including acidanthera, cannas, eucomis, dahlias, gladioli, galtonia, calla lilies, arisaemas, liatris, oxalis and tuberous begonias.
  • Clear spring bedding to make way for summer blooms.
  • Continue to deadhead spring flowering bulbs and camellias. Cut down the foliage from spring flowered bulbs six weeks after the flowers have died down.
  • Put supports in place for tall perennials.
  • Train climbers such as clematis while the shoots are still young and pliable.
  • Prune spring flowering shrubs such as Ribes sanguineum, Clematis armandii, pyracantha, chaenomeles and forsythia after flowering.
  • Clip beech, hornbeam, box, thuja, privet, Lonicera nitida and leyland cypress hedges late this month, making sure no birds are nesting in them.
Fruit and veg
  • Sow tomatoes under glass and, later in the month, sweet peppers, chillies, aubergines, melons and cucumbers.
  • Outdoors you can sow swedes, beetroot, maincrop carrots, Brussels sprouts, autumn cabbages, autumn/winter cauliflowers, calabrese broccoli, peas, Swiss chard, radishes, lettuce, mangetout, French beans, runner beans, turnips, endives, fennel, kale, kohl rabi, sweetcorn, courgettes, squashes (including butternut squash), pumpkins and spring onions.
  • Continue to earth up potatoes regularly.
  • Keep soft fruit bushes well watered.
  • Put straw or other liners under strawberries to protect the fruit from grey mould.
  • Cover or put up a barrier (of fine mesh/plastic film) 45cm high around carrots to protect them from carrot fly. Cover cabbages with a similar material to keep off the cabbage white butterflies.
  • Start harvesting your asparagus, lettuce, radishes, rocket, baby potatoes and overwintered onions.
General tasks
  • Mow your lawn weekly to around 2.5cm, longer if a drought is forecast. This is your last chance to re-seed any dead patches before the summer.
  • Use a ‘weed and feed’ product on your lawn, if you didn’t do it last month.
  • Keep on top of the weeding.
  • Apply summer shading to your greenhouse towards the end of the month to protect plants from scorching.
  • Ventilate greenhouses during warm days, but remember to close them up in the evening.
  • Scoop duckweed and blanketweed out of ponds and re-stock with aquatic plants.
Plant of the monthBerberis x lologensis 'Apricot Queen'

Berberis x lologensis 'Apricot Queen' is an evergreen barberry which grows to 3m height and spread with an arching, or rather messy, form. In mid to late spring bright apricot-orange flowers appear followed by purple fruits. A great low maintenance option for a part of the garden which needs cheering up. Find out more...

Problem of the monthChrysanthemum leaf miner

The chrysanthemum leaf miner causes white spots on chrysanthemum leaves (or related plants) which then expand to become white tunnels (or 'mines'). Damage on outdoor plants occurs in May, June or late summer, but indoors this pest can strike at any time. Severe infestations can reduce the healthy leaf surface to such an extent that the plant wilts. Remove affected leaves as soon as you spot them. Insecticides can be effective. Find out more...

In the news

Ash dieback disease reaches 1,000 sites

According to DEFRA figures ash dieback disease, which was first identified in the UK at a Buckinghamshire nursery in February 2012, has now reached over 1,000 UK sites. The latest figures identify 27 nurseries, 407 recently planted sites and 621 other locations (eg established woodlands) where the disease has been detected.

Good crop predictions for 2015

The dry and sunny weather last month has boosted many UK crops. Glasshouse grown tomatoes have arrived early and Waitrose is already stocking UK grown varieties. On tree fruits early blossom is being greeted by pollinating insects who are also enjoying the fine weather, the pear crop is anticipated to particularly benefit. And as we enter the asparagus season the largest ever UK crop has been predicted with half a million kilograms of spears expected to be produced this year.

RHS launches schools website

As part of their school gardening campaign the RHS has launched a new website to encourage more schools and youth groups to join. They will become part of the 19,000 existing participants - which includes 59% of UK primary schools and 47% of secondary schools. The website is aimed at both teachers and students. It provides lesson plans, RHS growing advice and allows participants to upload progress updates, which can contribute towards achieving the RHS School Gardening Award.


Crop rotation

PotatoesPests and diseases can be a real problem in vegetable plots and one highly effective way of minimising them is to use crop rotation. By annually changing, or rotating, the type of crop you grow in each plot, you will reduce the build up of pests and diseases (such as eelworms, clubroot and onion white rot). It will also help to maintain food levels in the soil as different crops require different proportions of nutrients.

Crop rotation can be carried out in all but the smallest vegetable plots. So long as you have the space to have at least 3 separate beds, you can rotate your crops. If you have a smaller area you can still use the principles of crop rotation to take a ‘year off’ growing certain crops to allow pests and diseases to reduce and nutrient levels to recover.

With 3 plots you will need to group your crops as follows:

Group 1 – Potato family (potatoes and tomatoes)
Group 2 – Legumes (peas and broad beans), onions (onions, garlic, shallots and leeks) and roots (eg beetroot, carrots, celeriac, celery, parsley and parsnips)
Group 3 – Brassicas (eg cabbages, cauliflowers, Brussels sprouts, kale, radishes, rocket, kohl rabi, broccoli, oriental greens, swedes and turnips)

If you have 3 separate plots then you would plant them in this order:

Plot 1 Plot 2 Plot 3
Year 1 Potatoes Brassicas Legumes/Onions/Roots
Year 2 Legumes/Onions/Roots Potatoes Brassicas
Year 3 Brassicas Legumes/Onions/Roots Potatoes

In year 4 you return to the year 1 layout, and so on.

The order of planting is important to maximise the benefits of crop rotation. For example, legumes deposit a lot of nitrogen into the soil through the bacteria which grow in their root nodules, which can then be lapped up by the subsequent nitrogen-hungry brassica crops. Potatoes help to break up the soil, which makes it easier for root crops to grow there the following year.

Some crops don’t need to be included in rotation systems because they have less of a tendency to suffer from built up pests and diseases. Therefore they can be added in with any group, or simply grown wherever you think you’ll have the space each year. These include:

  • French beans and runner beans (or they can be included as part of the legumes group, although they have less of a tendency to attract soil pests and diseases)
  • Peppers and aubergines (or they can be included as part of the potato group as they are from the potato family, although they have less of a tendency to attract soil pests and diseases)
  • Courgettes
  • Swiss chard
  • Sweet corn
  • Spinach
  • Salads (except those listed above)

In addition, perennial crops which require permanent planting can’t be rotated. These include, for example, rhubarb, artichokes, comfrey and asparagus.

Find out more about crop rotation, including a rotation plan for 4 or more plots.


What's on this month

With its bank holidays and major garden shows, a lifetime of garden events are being squeezed into this May! Here are just a few of them:

  • 1st & 2nd May - Toby Buckland's Garden Festival, Powderham Castle, Kenton, Exeter, Devon.
  • 2nd to 10th May - Bluebell Festival, Enys Gardens, Penryn, Cornwall.
  • 7th to 10th May - RHS Malvern Spring Show, Three Counties Showground, Malvern, Worcestershire.
  • 14th May - Red Cross Great Summer Garden Event, Cound Hall, Cound, Shrewsbury, Shropshire.
  • 14th May - Shakespeare's Plants And Gardens Lecture, Painshill, Cobham, Surrey.
  • 14th to 17th May - Summer Homes And Gardens Fair, Ripley Castle, near Harrogate, Yorkshire.
  • 16th May to 7th June - Chelsea Fringe, various locations in London.
  • 17th May - Container Growing Workshop, Tatton Park, Knutsford, Cheshire.
  • 17th May - Guided Garden Tour, Pentillie Castle and Estate, Saltash, Cornwall.
  • 18th to 29th May - Azaleas In Bloom, Borde Hill Garden, Haywards Heath, West Sussex.
  • 19th to 23rd May - RHS Chelsea Flower Show, Chelsea, London.
  • 21st May - British Mountain Flowers Course, Cambridge University Botanic Garden, Cambridge.
  • 29th & 30th May - RHS London Rose Show, RHS Horticultural Halls, London.
  • 29th to 31st May - Holker Garden Festival, Holker Hall and Gardens, Cark-in-Cartmel, Cumbria.
  • 30th & 31st May - Hatfield House Garden Show, Hatfield House, Hatfield, Hertfordshire.