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Dec 20

Biological pest control by natural predators and parasites

By chadchaffin | Gardening

Biological pest control has, of course, been around for millions of years, so the concept is not new. Ladybirds have always fed on aphids, frogs have always eaten slugs and birds have always devoured juicy caterpillars – the list goes on. Sadly the proliferation of chemicals used in farms and gardens in the 20th century often upset the natural balance of the ecosystem, removing micro-organisms from the soil and disrupting the food chain.

Pesticides caused collateral damage to the friendly creatures as well as the ones targeted, which also adapted to become more resistant to everything that man could throw at them, clearly an unsustainable course. When discussing biological pest control we need to consider it in two ways. Firstly, what can we do to harness the natural predators in the garden to work for our benefit, and secondly, what can we introduce to control specific pests?

It starts with the soil

It all starts with the soil. Feeding your soil with compost and organic matter will encourage the development of a healthy population of micro-organisms and bacteria, processing nutrients for plants and forming the first link of the food chain. Strong, properly nourished plants are also more likely to recover from and survive pest attacks. Providing wild patches, a pond, habitats and nesting sites for predators will all help to sustain a balanced ecosystem, with nature keeping things in check. Ladybirds, hoverflies, lacewings, beetles, frogs and toads, hedgehogs and birds are all examples of creatures that will help police our precious plants. Some slugs will eat other slugs. 

A modern solution

Biological pest controls for gardeners have  developed over the last 25 or so years as research and technological advances have enabled the controlled breeding of predatory or parasitic organisms that are specific to control various pests. The great thing about these is that the solution never becomes the problem; they will do their job but won’t persist in the garden or become an infestation in their own right.


Nematodes are the most commonly used biological control these days to control a wide range of pests. They are threadlike microscopic worms that live in the moisture surrounding soil particles. When they come into contact with their target pest they will multiply inside it, causing it to stop feeding and die. They have a finite life of a few weeks, either because they have exhausted the supply of host pests or because they themselves have become prey for native species that exist in the soil.
Nematodes arrive in a pack containing several million, which is added to water and applied using a watering can or sprayer, when the soil temperature is warm enough and when the pest is active. They are virtually invisible to the naked eye, safe on food crops and will not harm pets, children, wildlife or bees.

  1. Nematodes for slugs

    Proven and most effective against immature slugs under the soil surface, preventing them from reaching maturity to reproduce, their presence has also been shown to deter larger slugs. Each application is active for around six weeks, after which another may be needed depending on what you are growing. Usage should be able to be reduced over time as the slug population comes down to manageable levels.
  2. Nematodes for vine weevils

    This was the first nematode to be available for garden use and was a true breakthrough in controlling the very destructive larvae of this difficult pest that lives mainly in pots and containers. It can be applied in spring or autumn, stopping the larvae from eating away whole root systems and killing them before they develop into adults. Nematodes can also combat carrot root fly, cabbage root fly, leatherjackets, cutworms, onion fly, ants, sciarid fly, caterpillars, gooseberry sawfly, thrips and codling moth.

    This cocktail of various nematode species, sold as Nemasys Natural Fruit and Veg Protection, is designed to target pests when they are active, particularly useful early in the season when plants are most vulnerable. Used as a programme of two-weekly treatments after planting out, the gardener does not have to worry about application times or thorough investigations as to what the pests actually are. Alternatively, use to treat at specific times for particular pests. Caterpillars on leaves need to be directly contacted by spray for control.
  3. Nematodes to deter ants

    If ants are a problem then this nematode species will repel them from the treated area. It does not kill them but will encourage them to seek an alternative nest site.

Other biological controls

  • Ladybirds to control aphids
    Both larvae and adult ladybirds can be introduced into the garden and will get straight to work feeding on greenfly, blackfly and whitefly. If there is enough food they will stick around, but you can further encourage them by providing a ladybird shelter to give them a place to rest and multiply, and a ladybird feeder to see them through any lean times. An established colony will continue to be of benefit for many years.
  • Encarsia for controlling greenhouse whitefly
    A tiny parasitic wasp which lays its eggs in young whitefly scales, destroying them in the process. It should be introduced on low-medium infestations, and will give protection over a long period. Supplied as pupae from which the wasps will hatch when hung in the greenhouse. The best coverage is achieved using a programme of three applications 14 days apart.
  • Phytoseiulus for controlling red spider mite
    A tiny predatory mite which feeds on the red spider mite, used mainly in greenhouses. It breeds faster than the pest, so will outnumber it relatively quickly depending on the level of infestation. When there are no red spider mites left to eat, the predators will also die out.
  • Aphidius for control of aphids under cover
    A slender black insect about 2mm long that lays single eggs into immature aphids killing them as the young aphidius develops. One female can lay 100 eggs in her lifetime, so population numbers will grow rapidly until full control is achieved
  • Predatory mites
    This phoretic mite (sold as Mighty Mite) has a voracious appetite and a rapid reproduction rate at temperatures above 10ºC (50ºF). Primarily a soil-dwelling predator, it feeds on the larvae of dipteran flies, fungus gnats, sciarid flies, eggs and young maggots of the housefly, blowfly, stable fly and flesh flies. It also feeds on vine weevil larvae, cutworms, woodlice and springtails. It can be applied to pots and containers or direct onto the soil and is also effective added to mature compost heaps. When the compost is used, it will contain a population of mites ready to go to work against soil dwelling pests. 1000 mites will treat up to 4sq m.
  • Hypoaspis for control of sciarid flies (fungus flies)
    Sciarid flies are 3-4mm long black flies that jump or hover over the soil surface in the greenhouse and around houseplants where compost is warm and moist. The small white larvae live in the top few millimetres of compost, attacking rooted cuttings and seedlings. Both adults and larvae of hypoaspis feed on these larvae. One treatment remains active for four to five months.
  • Cryptolaemus for control of mealybugs
    These ladybird beetles love eating mealybugs on ornamentals. With a life cycle of several months one treatment is sufficient for an average greenhouse or conservatory although severe infestations may need more.

From Kitchen Garden Mag

Dec 19

Growing Gooseberries: A few notes for starter

By chadchaffin | Gardening

Gooseberries are often overshadowed by their more colourful soft fruit compatriots, such as raspberries, blueberries and blackcurrants. But their distinctive flavour is something not to be missed whether cooked or eaten fresh.

The gooseberry, Ribes uvacrispa, has its origins in Europe and parts of Africa and Asia, and has been cultivated in Britain from at least the late 13th century. In the 19th century gooseberries even developed into something of a craze with over 170 gooseberry clubs and fiercely contested gooseberry competitions. Today, gooseberries may not be the first fruit we think of growing, but they can certainly bring something distinctive to the kitchen table. Eaten raw they can have a tart taste but become sweeter the riper they are.

In the kitchen they are as versatile as any other soft fruit. Bare root bushes should be planted between early autumn and late winter, and prefer a moist, loamy soil and a sunny but sheltered site. Make sure you fork in some well-rotted organic matter and some general fertiliser pellets to the planting hole, spread the roots out and then cover with soil, heeling in to make sure the bush is secure. Water in and then spread a thick mulch (such as compost or bark) around the bush to help retain moisture in the soil. Because of their spreading habit, bushes should be planted approximately 1.2-1.5m (4-5ft) apart. If you wish to grow them as cordons (one main stem) then plant 30-38cm (12-15in) apart with accompanying bamboo canes 1.7m (5 1 ⁄ 2 ft) high connected by horizontal wires.


As with other soft fruit, birds love gooseberries so you will need to give your fruit some protection in the form of netting or a fruit cage. And not just in the summer – bullfinches are particularly partial to the young buds as they emerge in early spring. Gooseberry bushes need to be pruned in the winter, cutting back on old wood (four to five years old), as this will not produce any more fruit, and branches that cross or are low level as these can make the bush more susceptible to mildew.

It is also important to prune the centre of the bush if necessary, but don’t overdo it. This allows air to circulate in and around the plant and thereby make an attack of fungal disease less likely. Prune back young growth in June on bushes and cordons to five leaves; this helps to remove any mildewed growth and pests and encourages fruiting on the main stem. Gooseberries also make good container plants but these will need more watering than those planted in the soil.


You can harvest gooseberries at two points in the year. One is in late May-to early June when the under-ripe fruit can be picked, removing every other berry, for cooking purposes. Then by July the remaining berries will be much bigger and sweeter and can be picked for eating raw or for cooking.

Dec 17

How to Grow Lettuce: A very simple guide

By chadchaffin | Gardening

This familiar crop has been the main ingredient of salads for centuries. But over the years the humble lettuce has changed, offering gardeners a wider choice of colours and textures, creating the perfect salad accompaniment to any meal.

When to sow

Early sowings can be made from February to April for summer lettuce; these are sown into pots and pricked out into trays and grown on under glass until large enough for transplanting out on the plot after being hardened off in a cold frame. From April to August sowings can be made either direct into the plot or sown in pots and then transplanted to the plot. From early September through to mid October winter lettuces can be sown direct under cloches or raised in modules and transplanted out.
These will grow outside all winter and will mature from March-May the following year depending on the harshness of the winter. Gardeners with a cold greenhouse or polytunnel can grow lettuces throughout the winter.These are sown from September to November and will mature from January-April depending on how cool the greenhouse gets. When growing this type of lettuce try to keep the temperature under glass just above freezing for the best results. It is also important to give the greenhouse some ventilation on warmer dry days of winter to help avoid any grey mould problems.

Sowing the seed

Many gardeners sow their lettuces direct into the vegetable plot in shallow drills approximately 1cm (½in) deep.Then once they have germinated and the seedlings are large enough to handle they are thinned out or even transplanted into other rows. I find this method okay for early spring sowings, but as soon as the weather gets warmer the results can often be quite poor. Over the past 20 years I have rarely sown any lettuce direct outdoors, changing instead to sowing little and often all through the year in pots, often only growing 12 plants per variety. Sow a few seeds every two weeks under glass into flowerpots filled with moist seed-sowing compost, and then lightly cover the seeds with vermiculite.

Lettuces germinate better when sown cooler, so there is no need for a heated propagator, the pots can be stood on the greenhouse staging where the temperature will be between 10-15ºC (50-59ºF) and they will start germinating after seven to 10 days. When sowing lettuce during the summer and with the days getting hotter, gardeners often find it difficult to get lettuces to germinate, especially if there are several days where the temperature exceeds 21ºC (70ºF), as high temperatures will inhibit germination. To overcome this problem place the seed packets in the fridge the night before they are to be sown. This overnight pre-chilling seems to be enough to help the seeds cool down and then, once sown, they will germinate very well during these hot spells.

Growing on

Once the seedlings have germinated in the pots, prick them out (transplant) into cell trays (modules) and grow them on until they are ready for planting out. Before planting out, however, early sowings should be moved into a cold frame for a couple of weeks to gradually harden off. Lettuces will grow in any good soil that has been winter dug and enriched with organic matter. Before sowing or planting, give the soil a dressing of growmore fertiliser added at a rate of 60g per sqare metre (2oz per square yard), lightly raked into the surface of the soil. Seedlings sown direct should be thinned before the plants become too large to 15-30cm (6-12in) apart, depending on the size of the variety being grown.
The best time to thin out and transplant seedlings is in the evening when the temperature is cooler. After thinning, plants should be watered along the row straight away to help settle them back into their positions and recover overnight.

If using the thinnings as transplants to get another slightly later maturing row, this is best done straight away, removing a few plants at a time, planting before they wilt and thoroughly watering them afterwards so the roots are cool and wet. This will help them to recover quickly. Over the next week, water these transplants as necessary each evening to keep them turgid. Plants raised under glass and transplanted from modules get away a lot quicker with no root disturbance and producing a far superior lettuce.
Plant out each lettuce with a trowel at the required distance, water them in straightaway and you will see them grow away almost immediately.Throughout the growing season, fill up vacant spaces with later sown modular raised plants to keep the plot full and productive.

Early in the year, if the weather is changeable or very wet, windy and there is a risk of hail, cover the plants with a cloche made from Enviromesh or fleece for added protection. As plants grow, keep the weeds down by hoeing at regular intervals.
Two weeks after transplanting the plants are usually well established and watering can be stopped unless the weather is very hot and they begin to wilt; watering larger plants too much can encourage botrytis (grey mould) and mildew diseases.

Pests and Diseases

Occasionally, young seedlings or freshly planted out modules can be attacked by birds pecking the leaves; these can easily be deterred by covering the rows with some netting. Lettuces also make a tasty meal for slugs and snails, so it is best to protect these with whichever slug control you prefer to use to help combat this troublesome pest.
Lettuce root aphid and leaf aphid (greenfly) can be controlled by using a suitable insecticide, but always check the label before spraying to see how long after treatment you can safely harvest the crop.

Alternatively, grow one of the lettuce aphid resistant varieties. Occasionally, downy mildew disease can be a problem, but these days this is less so since the introduction of mildew resistant varieties. Grey mould is normally only a problem during very cool, damp weather conditions or on lettuces that are grown under glass through the winter with insufficient air circulation. If this is seen, plants should be destroyed to avoid the disease spreading to other plants.


Always try to cut lettuces one to two hours before you need them, wash immediately and place the leaves in the fridge to crisp up for that perfect salad. When preparing, either tear away the leaves
from the stem or cut using a plastic knife to help stop the leaves browning at the base while in the fridge for a few days.
When choosing a lettuce that produces a firm heart, always feel along the row and cut the one that feels the fullest; this way you will always be using the most mature lettuce first and helping to avoid wastage and stopping older lettuces running to seed. When selecting a loose leaf variety, this is easier because you can either cut the whole lettuce or pick the required amount of leaves from the plant needed to garnish your meal.

Pictures: Andrew Tokely and Kings Seeds

Credit: Kitchen Garden Magazine

Oct 26

How to care for and when to fertilize Rhododendrons

By chadchaffin | Gardening

There’s nothing shy and retiring about the rhododendron family – the colours are vibrant, the flowerheads large and voluptuous – and the delicious fragrance of Rhododendron luteum (commonly known as the yellow azalea) drifting in the air will stop you in your tracks. To see them in their full glory, visit the woodland garden at Bowood House in Wiltshire during May and early June, when the mature glades of rhododendrons are in full and magnificent bloom. Immense undulating drifts, some reaching ten metres high, blend brilliant- and subtle-hued shades along pathways that wind through the 70 acres, where carpets of bluebells fringe the paths.

Successive generations of the resident Lansdowne family have been planting this hillside with rhododendrons since 1854. The third Marquis established the original planting, while the fifth expanded the garden and added many more varieties. The current Lord Lansdowne (and ninth Marquis) continues this tradition in a very hands-on manner. He loves nothing more than escaping his other duties and disappearing across the parkland in his battered four-wheel drive for a bit of woodland management: it may be clearing land with the help of a specially adapted digger, pruning or planting. Tucked well away, there’s a shed where he can get on with repairing tools and machinery, and a modest greenhouse for propagating seed he has gathered and growing-on cuttings with the help of a misting unit. Rhododendrons root readily from layering (making a shallow cut in a low-growing branch and pinning it to the ground), so he also uses this technique on selected specimens to increase the collection.

How to Identify Rhododendron Species

From Visually.

Fortunately, there’s no shortage of things to keep the Marquis happily occupied for the foreseeable future and even in such an established setting there are opportunities for planting new areas. Most recent is the four-acre Jubilee Garden, which was begun in 2006 in a small valley with a stream at its centre. Compared with the rest of the woodland garden, it is still in its infancy, but it has allowed Lord Lansdowne to make his own mark as he has planted it with favourite varieties and extended the season of interest by adding other shrubs, including hydrangeas, magnolias, cornus and eucryphia. Few of us have the acreage or the legacy of planting that exists at Bowood, but for anyone who has more modest inclinations to grow rhododendrons, a visit here will provide colourful inspiration.

Where to grow Rhododendron

As a general guide, the smaller the leaf of the rhododendron, the more sun-tolerant it will be. Large-leafed specimens are woodland plants and, to grow well, they need the shade and shelter provided by a canopy of mature deciduous trees. Compact and dwarf varieties and evergreen and deciduous azaleas are all suitable for container- growing in ericaceous compost. They must not be allowed to dry out (or become waterlogged) and should be watered with rainwater.

The menace of the wild rhododendron

There’s no doubt that the sight of a hillside covered in the wild purple Rhododendron ponticum in full bloom is very attractive, but it comes at a great cost to the native flora and fauna. Since it was planted as cover for pheasants in Victorian times, it has thrived in the damp conditions in the north and west of Britain and taken over great tracts of countryside, squeezing out other plant species and proving very unwelcoming (and poisonous) to wildlife. It is also incredibly difficult to eradicate.

A single large bush is able to produce up to one million seeds in a single year, so even if the parent plant is removed, it still requires several years of controlling the seedlings. If all of this was not worrying enough, in recent years it has also been established that it is host to the plant disease phytophthora, which threatens to kill many of our favourite native shrubs and garden trees. However, two things can be done to help – firstly, buy rhododendron cultivars (never R. ponticum) from reputable specialist growers and, secondly, work as a conservation volunteer assisting organisations including the National Trust and the Woodland Trust with clearance programmes

Planting tips for Rhododendrons

Acid soil is essential for most varieties and it is important that it has moisture-retentive qualities. The evergreen foliage provides structure in the garden throughout the year, but can be dull once the blooms have finished. To extend the flowering season, mix rhododendrons with other acid-loving shrubs, such as Japanese maples, magnolias, cornus and pieris. The dense canopy and shallow roots of mature rhododendrons prevent other plants establishing nearby.

Choose varieties carefully to fit the scale of your garden: left to their own devices, some become very large. There are many lovely pastel-hued cultivars if vibrant combinations are not to your taste. Buy plants when they are in flower so you can be sure you like the colour of the blooms. To plant, prepare a large hole and incorporate plenty of leaf mould and well-rotted compost into it. Rhododendrons are shallow rooters, so ensure the rootball is level with the surrounding soil. Water well and mulch with leaf mould, composted bark or pine needles (not nutrient- rich animal manure or lime-rich spent mushroom compost), but keep the stem free of mulch.

Types of rhododendrons

  • R. augustinii  Striking violet-blue funnel-shaped flowers on a small-leaved shrub; 1.4m-1.6m high.
  • R. ‘Loder’s White’  Upright clusters of mauve-pink buds opening to trusses of slightly fragrant trumpet-shaped white flowers up to 10cm across; 1.5m-2.5m high.
  • R. luteum (yellow azalea) Scented blooms on a deciduous shrub with vivid-hued autumn foliage; 2.5m-4m high.
  • R. campanulatum x pictum  Natural hybrid bearing pale lilac-pink flowers with speckled throats; attractive large glossy leaves; reaches 1.5m in ten years.