Friday 7 November 2014

A gallery of pumpkins

When it comes to growing pumpkins, I'm happy to leave the cultivation of giant specimens to others. I've grown a few up to spacehopper size in the past, but it never seems to be the tastier varieties which grow really big. Football sized is about right - the green Berrettinas on the bottom shelf here are just a little but larger than that, and bowling ball sized - the green Futsus in the middle - will do just fine as well. 

I've also never got round to growing them on the compost heap, as others swear by, and which can give you highly productive plants as I noticed on my recent visit to Great Dixter. I start my squash seeds in pots and once they have at least two true leaves, plant them out in a bed with lots of organic matter - including kitchen compost - dug in. Before planting, I cover the bed with sheet plastic, and cut holes in it to plant the seedlings through - this keeps the moisture in and the weeds down. I also give the plants a mesh trellis to scramble up, which has two advantages: it keeps the squash plants more or less to the bed you planted them in, rather than rambling all over the allotment, and it means most of the fruits grow off the ground and are less vulnerable to slugs, snails, and rotting where the thin skin is laid on damp grass or soil.

In most years, the foliage starts to die off towards the end of September, and by mid-October, the fruits are laid bare across the bed - sometimes attached to the main plant by a mere thread. The squash will be ready to pick and bring inside then (squash ready for picking will also sound distinctly hollow when tapped). This year, with such a warm autumn, the plants stayed lush and green right through to the middle of October and I lifted them last week when our first frost threatened (frost will turn the pumpkins to mush).

Once safely indoors, they can be stored somewhere bright and warm - by the kitchen window, in my case - to be 'cured'. In warmer climates with longer growing seasons, pumpkins can be cured out in the field, but it's getting a bit chilly for that here in England now. Curing hardens the skins (which helps them to store for longer) and develops the flavour. You should really store the pumpkins for 10-14 days in the warm and then remove the fruits somewhere cooler, ideally at a steady 12 degrees Celsius or so, for storage, but mine stay happily in the kitchen window throughout the winter months. Those still uneaten after Christmas will store right through into the next spring.

Incidentally, I've never been quite sure which types of squash can call themselves pumpkins. Although we traditionally think of pumpkins as orange Hallowe'en lanterns, I would also call the Berrettina Piacentina and Marina di Chioggia here pumpkins, as well as other green varieties like Crown Prince. I've seen it suggested that one thing that distinguishes a pumpkin as a particular type of squash is that its seeds are edible.

Berrettina Piacentina: Franchi Seeds of Italy

Monday 20 October 2014

Great Dixter: a riot of colour

The wonderfully bold, lush gardens at Great Dixter look beautiful at any time of the year, but perhaps especially so at this time of this year, towards the end of an elongated summer with the air still full of warmth and the plants at full maturity. I was lucky enough to be visit on a gorgeous fine day last week.

A view of the oast house (sadly long out of use) from a corner of the sunken garden.

One of my favourite views, through the blue garden into the wall garden. I defy anyone to resist squeezing through the gap and exploring up the steps.

The impressively espaliered pear tree against the wall of the house in the blue garden (just visible in the top right in the previous picture). The Gunnera manicata in front of it is growing happily in a giant pot.

The seasonally-changing pot display in the wall garden is dominated by deep reds and brilliant yellows at present.

This is how to grow pumpkins on a compost heap - it helps if your heap is around 10 feet high.

A sneaky peek into the sunken garden from the meadow in front of the main entrance to the house. Great Dixter has many of these tantalising glimpses into its many gardens.

There are a couple of disused wells in the grounds, which now form stunning planters.

The main entrance to the house, which dates back to the mid-15th century, flanked by a mass of containers of lush flowers and those reds and yellows again.

Since the death of Christopher Lloyd, the owner of the Great Dixter estate, in 2005, the house and gardens have become a charitable trust, with the gardens  still overseen by Fergus Garrett, who devised the innovative and influential planting schemes alongside Lloyd.

The nursery, which sells many of the varieties grown in the gardens, is open all the year round. The house and gardens will reopen from March 28th 2015.

Further info from

Thursday 11 September 2014

Grow your own wasabi paste

It's a open secret that the little piles of green paste that come with your sushi lunch box are not true Japanese wasabi but ordinary grated horseradish with some green food colouring added to it. So you get all the heat of the condiment but none of the fresh herby tang of genuine wasabi (Wasabia japonica), also known as Japanese horseradish. Like horseradish, wasabi is a member of the Brassica family, and it's the rhizomes, the swollen stems which are often thought of as roots, which are harvested and grated to make the classic Japanese wasabi condiment.

Less well-known is the fact that the wasabi plant is in many ways well suited to growing in the UK. It's a reasonably hardy perennial, so it will survive a cold winter and its ideal habitat is cool, moist shade.

In Japan, wasabi is a highly-prized and expensive crop - reputed to be difficult to grow. It's often grown hydroponically in moving water, much like watercress, and this sawa wasabi is considered superior to soil-grown plants. But if you don't have access to a sparkling fresh stream, the plant will be happy grown either in the open ground or a pot. What it doesn't like is strong sunshine and heat.

I started off growing wasabi in a shady corner under a clematis. The plant survived quite happily but didn't develop much in the way of root - probably because although shaded, the location was too dry. I've since had much more success growing the plant in large pots, where I can choose the best position to grow them and also control the water supply.

So you need a shady location - dappled shade is OK - and somewhere which will stay cool in summer, ideally, it should remain below 20 degrees Celsius. It also needs to be kept well-watered: if your shady borders also tend to be dry, consider growing in a pot instead. It's also worth trying out a drip method of watering - even if that's just a plastic bottle with a hole in it shoved into the soil - to ensure the soil stays moist.

It takes two to three years for the thickened stem, or rhizome, to develop. You'll know when the rhizome is getting ready to harvest, as the swollen stem will be visible just above ground level, ready for you to lift.

The thickened steam, the rhizome, is visible above ground
when the wasabi is mature.

In the meantime, while you're waiting, the leaves, stems and flowers are all edible. The round succulent leaves will give your salads a crunchy kick, and the delicate white flowers which appear in spring have an elusive peppery flavour.

The succulent leaves of the wasabi plant can also be picked and eaten,
adding a mustardy crunch to salads

You will find the leaves and stems are also extremely popular with slugs and snails. It's another reason why wasabi grows better for me in a pot: I can keep them under maximum security conditions, surrounded by copper, ground-up eggshells and with the pots kept well away from encroaching foliage. Even so, I find I have to do the rounds and inspect under leaves very regularly to catch them before they decimate the crop.

Harvesting wasabi
The wasabi will be ready to harvest at the end of the second year when the thickened portion of the stem is about an inch in diameter. There is no harm at all in leaving it in the ground for longer. Dig up the plant and wash well in lots of cold water, trimming off any fine roots and the remaining leaves.

Cleaned, but not yet trimmed: freshly-dug wasabi.

You will be left with a knobbly green rhizome, pitted with leaf scars. This will keep in the bottom of the fridge, preferably wrapped loosely in a clean damp cloth, for a few days. Scrub the root well and then grate, on a microplane or zester to get your fresh wasabi paste. After some experimentation, I found the nutmeg grater gave me the best results. The paste should be moist and squidgy and free from fibres - it should hold its shape if you press it. Leave it to 'rest' for about 10-15 minutes then eat as soon as possible as it will start to lose flavour if it is left standing for too long.

Replanting for next year
The easiest way to propagate your wasabi plants is by separating the small plantlets which form at the base of the main stem and planting these up. Late summer is a good time to do this so that the new plants have a chance to establish themselves before winter sets in, although they may well have to be nurtured in a small pot at first before planting out.

I've bought wasabi plants from the Scottish nursery Poyntzfield Herbs and also once from my local garden centre when they had a batch in. Plants are also available from Suttons as part of its James Wong Homegrown Revolution range and from The Wasabi Company, which also sells fresh trimmed rhizomes.

Further reading
The history of wasabi and its place in Japanese culture:
Growing wasabi hydroponically:
The health benefits of wasabi included in a general article on Steamy Kitchen:

Friday 5 September 2014

Seeds that never go out of date

You can rely on sunflowers to cheer up the allotment at this time of year. This one, the aptly named Giant Single sunflower, was grown from some very out-of-date seed which I sowed back in April on the basis that I might as well use them up as buy fresh. I think the packet recommended sowing by end 2009.

Expiry dates on seed packets can often be used as guidelines rather than hard and fast rules. I have successfully germinated out-of-date lettuce, tomato, chilli, and beetroot seeds. Anything from the season after the expiry date, to several years in the case of lettuce in particular.

Of course germination rates are nearly always better with fresh seed and a lot depends on who the seed has been stored in the meantime. If seeds are kept cool, even cold, in the dark and, most importantly, dry, they can stay viable for years.

I've always been told that parsnips and carrots should be sowed when very fresh and always buy these new each year. Parsley, another member of the umbellifer family, doesn't germinate well if not sown within a year, but with most other veg, it can't hurt to sow any leftover seeds in modules or the open ground and see what comes up. In the case of these best-by-2009 sunflowers, around 50% germinated and there are another two Italian White sunflower plants about to burst into flower as well.

Monday 11 August 2014

Through the keyhole - an African garden in London

A keyhole garden is a type of raised bed which originated in parts of Africa struck by droughts interspersed with torrential rain. The charity Send A Cow, which provides livestock and training in natural organic farming techniques to poverty-stricken parts of Africa, developed the keyhole garden as a sustainable way to help families to become more self-sufficient, to grow more vegetables in a restricted space, at very low cost, and reliably, despite the vagaries of the climate.

The basic principles are simple. The keyhole is a circular raised bed, with, crucially, a tube or basket in its centre which is filled with kitchen compost: peelings, outer leaves, eggshells, the usual stuff you throw in the compost bin. A pathway is cut out of the circle leading from the edge to the central basket so that you can easily refill the tube and indeed reach all parts of the keyhole garden with ease. Viewed from above the bed looks keyhole-shaped, hence the name.

Permaculture - sustainable gardening
The keyhole garden is meant to be as low-cost and sustainable as possible, so the bed is filled, lasagne style with various types of organic matter: cardboard (lots of cardboard), dried leaves and grass cuttings, coffee grounds, leaf mould, straw, newspaper, manure, wood ash, and only topped with a layer of topsoil to plant your first seeds or seedlings into.

The walls of the garden can be made from stones, rocks, bricks, anything you have to hand. A quick search on the web throws up keyhole gardens edged with old wine bottles, sandbags, car tyres, and wooden blocks.

Increased yields
To a large extent the keyhole garden looks after itself. The soil in  the bed is fed by nutrients from the compost breaking down and seeping from the central basket. You should only really need to water the central basket - in Africa, household grey water is used to keep the central basket moist - and the shape of the bed should ensure that water is distributed to the plants.

At 2 metres across - the maximum recommended diameter both for ease of access and to ensure plants near the perimeter still get moisture and nutrients form the central basket - the keyhole garden can reliably supply vegetables on a year-round basis.

I was intrigued by the pictures of different keyhole gardens in Lesotho and Uganda on the Send A Cow site and also at Inspiration Green, here Instantly appealing, some look as thought they have been thrown together, others more like permanent structures. As they use whatever materials are to hand and can be recycled, no two keyhole gardens look exactly the same. 

We may not have the specific challenges of poor thin soil and dry conditions that they do in Lesotho or Uganda, but the sustainability and permaculture aspects of the keyhole garden appealed very strongly to me, and I wanted to try building one on the plot. 

I see no reason why this idea of a central nutrient source shouldn't work in other raised beds as well. Obviously the circular shape of the keyhole garden means there are no hard-to-reach corners where the goodness from the compost never reaches, but the principle still holds good.

I always like the idea of specialist beds. Here is where the nutrient-rich growing medium will feed leafy salads, or get the tomatillos and/or physalis off to a flying start. The compactness of the keyhole garden also makes it easy to protect - from birds, or slugs, for example. Great for courgettes, too, for those whose conventional compost heap is a bit too stringy and uncomposted to successfully grow cucurbits.

The first task is to find an area for your keyhole garden and clear the ground, digging out any weeds and roots. There are no hard and fast rules about size. Send A Cow says that 2metres in diameter is a good workable maximum size. My cleared area didn't quite match that: the diameter here is 1.8metres.

To measure out the area of your keyhole garden, push a stick in the ground where the centre will be. Tie string to the stick and measure out enough string for the radius of your garden (90cm in my case). Tie the string at the other end to a second stick, then extend the stick out the full length of the string. If the ground is soft enough, you can drag the stick marking the circumference around the centre stick to make a line on the ground. The ground was pretty hard when I did this, so I marked the 90cm radius with pea sticks at intervals. I'm afraid you have to peer at this photo to spot the pea sticks but they are there.

Where the sticks have marked the circumference, start laying the external wall for the garden.

Here in north London we don't have a ready supply of boulders and rocky outcrops that they do in Lesotho, but what we do have is a lot of people making improvements to their properties. And where there are extensions being built, there will also be skips out in the road full of old bricks.

It took me just two skip-diving missions to find 40 bricks to line my keyhole garden and I didn't have to travel further than two miles from my front door. The rules say you should always ask for permission before removing anything from someone else's skip, and I'd go along with that. Apart from the etiquette aspect, once you've told the builder, or the householder, about your brick recycling project, they often offer help, whether it's just loading up the boot of your car with their bricks, or to tell you there's building work on the go just around the corner.

Next, add your central basket. Again, there is no precise material that should be used, so long as it's permeable. You can use sticks placed close together, you can weave your own with pliable canes such as willow, or you can reuse an old piece of wire mesh as I did here, bending it into a cylinder and securing with wire ties top and bottom. I also used the pea sticks to support and secure the mesh into position in the middle of the bed.

Now create the pathway that makes the keyhole shape of the bed, leading from the outside edge into the central basket. If it's feasible, it's a good idea to cut the keyhole path on the north side of the bed, the part of the bed that will be cooler and shadier, leaving the growing area sunny and south-facing.

Now it's time to start building up the bed. I used cardboard as my base layer: a good weed suppressant but also organic so it will decompose and help to enrich the soil. In Send A Cow's videos of keyhole gardens in Lesotho, they often scatter rusty tin cans over the base of the bed, to add iron to the soil. Here, newspaper covers any gaps in the cardboard.

As you fill the bed, you need to build up the sides as well. The bed can be as high as you like: these raised beds are great for people who can't bend down to ground level. The overall shape of the soil should be conical, with the soil level higher at the central basket and sloping downwards towards the outside the edge. The outer wall should rise above the soil level, otherwise soil will wash away over the sides when it rains. The next layer here comprises coffee grounds - Starbucks (and I'm sure the others do this as well) will bag up their leftover grounds for you to take away for free - and old grass cuttings ...

... and comfrey leaves for lots of good nutrients. But only the leaves - don't bury any root, unless of course you want to grow comfrey in the keyhole garden.

You can also add wood ash, leaf mould, manure. I added manure and then a tin layer of top soil to sow the seeds in.

The central basket has a smaller diameter than the recommended 30-50cm, but then the bed is smaller anyway. It does however need a lid to keep the kitchen compost from drying out: currently I have capped it with an upended coconut shell, so that the rainwater will still run down the sides of the coconut and into the basket. 

These Florence fennel seedlings were donated by a fellow allotmenteer and I've surrounded them with a copper anti-slug collar as a precautionary measure.

My resident allotment wreckers, the car and the fox, have been quite active over the last few weeks, so I added a net, lifted with hoops to keep them off the soil. Mr Tod, in particular, gets very excited by eggshells, and I really don't want to find the contents of the central basket scattered across the allotment. I may look for a more permanent framework and line it with fleece or clear polythene in the spring to create a keyhole greenhouse for early seedlings.

As well as the Florence fennel, I sowed seeds for two types of purple radish, Violet de Gournay and Hilds Blauer Herbst Und Winter , and some kailans (Chinese broccoli). These all germinated in 3-4 days and are growing strongly.

Further reading


Sunday 13 July 2014

Tomatillos - back from the dead

These photos show my tomatillo plants in rude health. Bushy, leafy, weighed down with little green lanterns which house the fruit, it's hard to believe that back at the end of April I was convinced the plants were dead.

I'd sown them at the very beginning of March, earlier than usual because last year they had needed a really long season to get going. By the second week of April the plants were rocketing away and had outgrown their 3-inch pots, the weather was warm and I planted them out in a newly-made raised bed. Of course, whatever the daytime temperatures, the nights were still cold and it was soon clear that I'd planted them out far too early. The three tomatillo plants (yes, there are only three plants in the bed) stopped growing and just looked spindly and unhappy.

I took pity on them and popped a homemade bottle cloche over each plant: take a 2-litre plastic water bottle, cut off the bottom, then cut off the neck where it begins to narrow so you are left with a long straight cylinder of clear plastic. That cheered them up a bit and they started growing again so that by the end of April there was foliage spilling over the top of the bottle cloches.

And then we had an overnight frost. I came up to the allotment to find my happy tomatillo plants had been reduced to green stems draped with withered, browning leaves. For a week, I left them, hoping they might recover, but nothing happened. Eventually I decided I would just have to start all over again with them and lifted the bottle cloche protecting the middle plant in order to pull the plant up, only to find that within the confines of the plastic bottle protector, there were indeed new leaves just beginning to sprout. It was only the tips of the plants, exposed to the below-freezing temperatures, which had died. I cut these dead leaves and stems away completely, replaced the cloche and went back to waiting.

After that the regrowth was fast and the plants are also even bushier than usual. They've taken over the bed, elbowing out the cucamelons behind them and hogging all the available light. So it appears that a rigorous prune early in the growing season might be beneficial to them although it seems like a rather risky procedure to carry out in springtime.

Thursday 10 July 2014

A quick tour of Hampton Court Palace Flower Show

Hampton Court Flower Show on the Tuesday - almost impossibly crowded by midday when the rain came down and everyone tried to squeeze into the marquees, but still a stunning display of plants and current garden trends. First stop as always was the Growing Tastes tent, to admire Franchi Seeds' accordion garden and to see what new herbs were on show from Highdown Nursery, Pennard Plants and Hooksgreen Herbs. Lots of Salvias this year, especially the tangerine, grapefruit and blackcurrant varieties with their flowers so brightly coloured they look almost neon, and fruit-scented leaves.

I scooped a Murraya Koenigii (curry leaf plant) from Plants4Presents (I should say 'another' as I accidentally waterlogged the last one I bought from them two years ago) and an Anthyrium niponicum, the Japanese painted fern, before setting out to tour the gardens.

Gluttony E-123, one of the conceptual gardens inspired by the deadly sins,
designed to highlight the over consumption and waste of food in western
(Designed by Katerina Rafaj, built by Purpleberry Consultants)

Wrath - Eruption of Unhealed Anger was also one of the conceptual gardens,
the centrepiece of which is the smoking volcano which produces a waterspout
every ten minutes or so, to shocked gasps from onlookers.
(Designed by Nilufer Danis, built by Landform Consultants Ltd)

In Bacchus, the designers have found a ingenious place to act as a wine cooler:
tucked under the steps. The garden includes a large specimen grapevine and
vine hedging to the rear, as well as tiered pools to represent an ever-flowing
supply of wine.
(Designed by Jean Wardop, built by Ricky Cole - RDC Landscape Design
and Construction)

I loved this bench sat squarely in the middle of a modern potager: cavolo
nero and tomatoes inside the box hedging. This is one part of the garden,
Hedgehog Street, a trio of suburban style gardens designed to be
(Designed by Tracy Foster, built by Concept Landscapes with Phil Game)

One of the other Hedgehog Street gardens (I love the mosaic). Great textural contrasts
with the grasses, which give ground cover for hedgehogs; and for humans,
surely the most comfortable looking seating area in the whole show.
The ladies from Ocean Spray demonstrate how to wet-harvest cranberries.
The farmers flood the fields and let the fruit float to the surface of the water
so that they can be scooped up.

I do like a living roof. I nearly missed this one in A Space To Connect & Grow, a
garden designed as a place for performances and workshops as well as for
relaxing. It makes extensive use of recycled industrial materials.
(Designed by Jeni Cairns in collaboration with Sophie Antonelli. Built by Juniper
House Garden Design)

Friday 27 June 2014

Fighting the slug and snail takeover

I don't know about your garden but the molluscs are taking over in mine. We had a wet winter in which it never really got properly cold and so hibernating slugs, snails and their eggs didn't get killed off in their usual numbers. Now after a reasonably fine spring, we had a warm wet start to the summer. Lots of lush green leafy growth means lots for slugs and snails to sink their teeth (oh, yes, teeth)  into. One single slug or snail can reduce a courgette or lettuce seedling to a bare stalk in one session: in addition to a rough tongue called a radula, they also have thousands of tiny denticles, or tooth-like protusions. 

I must have tried every single slug/snail barrier or killing method known to mankind over the years. The problem is that there is no one ideal solution for all situations. Not everyone likes the idea of killing the pests in large numbers. One of the easiest ways to get rid of slugs and snails is to scatter slug pellets around your precious plants, yet it's well-documented that slug pellets will harm other wildlife as well. I only use them when the slug numbers are overwhelming and only under netting or in the greenhouse to try to minimise the danger of anything else ingesting them. I wish I didn't use them at all and I dislike dealing with the messy slimy death the pellets cause.

You don't, however, have to kill your slugs and snails: there are various ways to deter them, whether through physical barriers, or what I think of as diversionary tactics. I've found that repelling them without killing them tends to work well in years when the slugs/snails are not around in huge numbers; in very sluggy years like this one, they will just slope off to eat something else. I don't, for example, usually bother with slug protection for my chilli plants: slugs and snails don't tend to find them very appetising. This year, I've lost several chilli seedlings to slugs and snails: there are so many more of the pests and if they can't get at the salad leaves, or the young courgettes, they'll chomp down on whatever they do find. It's tempting just to pick them up and throw them over the fence, but both slugs and snails apparently have a homing instinct and they will just come back, even if somewhat slowly.
Caught in the act: young courgette and squash seedlings are a
favourite target, also salad leaves, brassicas, and my wasabi plants,
which I have to keep almost hermetically sealed away from
both slugs and snails.

One of the most attractive options (to me anyway) is to biologically control them with nematodes: near-microscopic organisms which live in the soil, and will eat into slugs and kill it. The nematodes do not interact like this with anything else, so are harmless to other wildlife, and the slugs are eliminated (good), yet the killing happens remotely and invisibly to me (even better). But even this is no cure-all: it's expensive, it needs to be done every six weeks or so throughout summer, and is really only effective against slugs, because the nematodes work in the soil, and snails tend to live above ground. 

The best solution of all, if available to you, is to create a slug/snail-hostile environment as naturally as possible. A pond with frogs, a resident hedgehog family and a population of thrushes and other slug-eating birds will help to keep numbers to a minimum. And one thing I've learned recently is that I shouldn't really be aiming to eliminate the molluscs altogether: only some of the 30 different slug species that live in the UK eat your tender vegetables, they and the rest will also feed copiously on decaying vegetable matter and so are an important part of your overall garden ecosystem.
In a dry spell, the slugs and snails seem to disappear. But if you overturn
pots, peel back black plastic or look underneath decaying wood, the
chances are you'll find them hiding in the dark and damp.

The trick, I think, is to use methods in combination. I've resorted to using copper tape to protect pots and individual plants such as brassicas and squash on the allotment, plus a good watering with anti-slug nematodes when the conditions are right and I can afford it, plus using organic pellets in very specific closed environments where there is no danger of other wildlife ingesting them, plus morning and evening inspections around the garden and allotment when the weather is damp and after rain (when I will despatch the slugs as quickly as possible by snipping them in half with scissors). It's time-consuming, but slightly less stressful than losing all your squash or salad seedlings to a fat, but still hungry slug.

I've collated the methods I've used (some more successfully than others) into the table below. I'd love to know about any other effective ways to remove, deter or eliminate slugs and snails and make this as comprehensive as possible.

The Method
Kills slugs and snails
Harmful to other wildlife
Easy to apply
Requires reapplication
Messy corpses

This is what happens when a slug ingests a slug pellet: the methiocarb
in the pellet causes the slug to over-produce mucus and it dies of dehydration, 
leaving you with a nasty slimy mess. Any predator that tries to
eat the dying slug may well be poisoned in turn by the methiocarb
in its system.

Beer traps
Kill slugs and snails
Messy corpses to dispose of
They die happy
Ineffective against large numbers
Requires maintenance
Waste of good beer
Other traps, eg, grapefruit halves
Does not kill, pests congregate in grapefruit halves
Live slugs and snails to dispose of

Copper tape
Does not kill; the pests will go elsewhere
Environmentally non-invasive
Relatively expensive
Risk of trapping pest INSIDE the pot
Taped pots can be reused

A simple copper collar made out of a section of plastic water bottle
lined with sticky copper tape

Coffee grounds
Does not kill; the pests will go elsewhere
A LOT of coffee grounds needed for more than one or two plants; you will need to befriend local Starbucks or similar
Environmentally non-invasive – grounds good as mulch
Ineffective against large numbers
Sharp grit, etc
Does not kill; the pests will go elsewhere
Do you really want your beds full of grit?
Risk of trapping pests inside the barrier

Torchlight patrols
Now you have to kill them
Environmentally non-invasive
Disposal of corpses
Effectiveness depends on your vigilance
Morale-draining in face of large-scale invasion

Encouraging or introducing predators: birds, frogs, hedgehogs, geese, etc
Easier to achieve in a rural environment
Potentially highly effective
Requires maintenance at least initially
Potentially expensive outlay (digging out a pond, acquiring geese)

Introducing predators: nematodes
Not nearly as effective against snails, only slugs
Requires reapplication

There are around 30 different types of slugs that live in the UK,
only around 4-5 of which will out of choice eat your vegetables.
These are two of the bad guys: the imaginatively-named
black slug, top, and the red slug, above.

Further reading - US-based article on natural methods of curbing or eliminating slugs and snails. - some more ideas for getting rid of slugs and snails and a photo which almost makes them look pretty. - how to buy and use nematodes as a biological control. - how to make your own nematode soup (warning: the method is somewhat icky) - know your slugs: an identification table to UK species.