[Note: Much of this information is available elsewhere on UK420 or known to some and not others, but it tends to be scattered around the forums. Some information is contained in various people's Grow Diaries, some is in the Guerrilla Farming section, some is in the D.I.Y. section, some is in Problem Solving, some is contained in the FAQ. This is an attempt to summarise the major options in one place. If in doubt, use the Search function.]
There are a number of animals which can cause problems to outdoor-growing plants, and a number of methods for dealing with them.
Slugs and Snails
Slugs and snails will gladly feed on any young, soft plant, so your seedlings and freshly planted out crops are a feast waiting to happen. There are a number of ways to prevent slug and snail attacks, but they loosely fall into the categories of 'barrier' and 'distraction'.
'Barriers' work by placing an obstacle of some kind between the slug and the plant.
One of the most effective types used by growers on the forums has been the Copper Tape method. When a slug or snail slides over a copper surface, the motion of the animal combines with the liquid nature of the slime and the ions in the copper surface to induce an electro-chemical reaction which the slug finds very uncomfortable. Copper can be acquired from numerous sources, although the most effective sort is tape which is purpose-made as a slug-deterrent, and can be bought from good garden centres or online. This is one of the most popular and effective methods.
Other substances can be used as a barrier which also rely on the property of inducing discomfort in the attacker.
Crushed gravel can be spread around the plant in a ring, forming a surface the slug finds it uncomfortable to cross. Only certain types of gravel work, namely those consisting of fairly small, sharp particles. Gardenadvice.co.uk recommends using horticultural grit of between 4mm and 8mm in size; they also claim that vermiculite can be used similarly with up to 90% effectiveness.
In the same vein, some claim that sharp sand can also be used, as can crushed-up egg shells, although some doubt the effectiveness of doing this. It has been suggested that loft insulation can be used for a similar purpose, although it should be stressed that this is about as environmentally-unfriendly as it is possible to get, as the fibres in insulation do not degrade; whether it is any more effective than other measures is also open to debate.
Some have claimed to have great success using oats to deter slugs and snails, although this has the potential side effect of luring other wildlife (namely birds) who then feed on the oats. Dry bark is effective to the extent that slugs find its dehydrating nature hard to move against, but it has the downside of losing its effectiveness in the wet. Diatomaceous earth can also be used for a similar purpose, but its effectiveness is disputed and it is more expensive than other options.
smeagol offers another barrier suggestion:
It should be noted that the barriers mentioned so far are a deterrent in the same way that home security is a deterrent. By making your home more secure, you don't really make it impervious to break-ins - something which is pretty-much impossible - but you do make the hassle of breaking-in worth less of a burglar's time than other available options. The same applies to deterrents. Given a choice between struggling to deal with an unpleasant barrier and eating something else, the majority of slugs and snails will go elsewhere. This doesn't mean that it's completely impossible for a slug or snail to breach the barrier, but it does greatly lessen the likelihood of it happening.
'Distraction' techniques rely on providing a more attractive option to the slug, rather than making the seedlings less attractive.
The Beer Trap is a common distraction that relies on the gastropods' love of sugar and alcohol. A small container, such as a jam jar, is sunk into the ground and filled with a little beer (anywhere from a centimetre upwards). Containers placed on their side can be used to protect against rain. Slugs will be attracted to the beer trap and drown in it. It has some downsides in that: it can be susceptible to being rained-on; you must make sure that the beer content is kept topped-up from time to time; and you must make sure that the trap doesn't fill up with slugs, but the technique certainly works.
A more controversial method is that of using Slug Pellets. Slug pellets are made of a tasty cereal which has a slug poison - usually metaldehyde or, less frequently, methiocarb - buried inside it. They are usually scattered, reasonably scarcely, around the plants. Slugs will be attracted to the cereal, eat the pellets, and die from poisoning. Simple, eh? Not so, say the environmentally-oriented, who claim that the cereal bait attracts and then harms other animals - dogs, cats, birds, bugs etc. Pellet manufacturers naturally claim that very little damage is done. Whichever is true, metaldehyde pellets are overwhelmingly preferable as they are less toxic without being less effective.
There are a couple of issues specific to guerrilla growing which might weigh-in against slug pellets, however. The first is that some claim that, over time, the pellets decompose, get washed into the soil and affect the plants in a negative manner, leading to less pleasant smoke. The second is that, in order to dissuade birds and other creatures from eating the pellets, they are usually dyed a strikingly unnatural colour, such as fluoroescent blue. One pellet falling in the wrong place may therefore have the slight potential to blow an entire grow, so be careful.
Lastly, in barrier terms, there are Nematodes. Nematodes are a type of tiny worm which live in the soil and prey on slugs. They are available from garden centres. You buy them as a powder which has to be made into a solution and then watered into the ground around the plants. Nematodes are supposedly harmless to the plants, humans and other animals. They do need refreshing every so often, and doubts have been expressed as to their suitability for cannabis protection.
A more thorough consideration of the issues surrounding slugs as horticultural pests and the various means of dealing with them can be found at Cardiff University's School of Bioscience's Slug Control Page.
Rabbits and herbivorous mammals
Rabbits are natural herbivores and can chew through a crop in a very short time. Furthermore, things like gravel, copper tape and beer traps don't even break their stride, let alone stop them.
Fortunately, there is an environmentally-friendly way of keeping their bucked-teeth away from your hard-grown weed. Garden centres and DIY stores sell rolls of Chicken Wire or Rabbit mesh. This is simply a type of mesh fencing designed to keep curious fauna away from growing crops.
Your plants will need to be surrounded by a tubular cage of fencing at least a foot (12" / 30cm) in diameter and one-and-a-half to two feet (18"-24" | 45cm-61cm) high. A good rough way to do this is to use lengths of fence approximately four to five feet in length, 20" in height, then loop them round and fasten them back on themselves using plastic zip ties (also available from DIY stores and garden centres). These tubes can then be folded up for transportation to the grow sites. More detail can be found in BushBandicoot's article in the September 2004 newsletter.
The mesh used should be sturdy enough to take a few rabbit entry attempts, but sparse enough to let light through and facilitate growth. The mesh is not there to protect against all possible assaults, but simply to protect the plant until it is old and large enough to take care of itself (big, thick, woody stems etc.). A good-sized mesh has holes between 3/4 of an inch and about an inch and a half across. Some meshes have hexagonal holes, some have square ones. Good examples of sturdy cages can be found in iamafunkimunki's 2007 grow diary.
Bare metal mesh fencing can be seen from a surprisingly large distance away if the sun is at the right angle (especially if the mesh is quite thick) and may well draw suspicion depending upon the grow location. Mesh is available in both brown and green plastic, and in a form where the bare metal wire is covered with a mid-to-dark-green plastic coating. These types of mesh aren't any more expensive than the bare metal kind, and blend into the background nicely, being invisible at even relatively close distances. Try and buy this kind of mesh if you can, although any mesh is better than none.
The cages must be anchored to the ground to prevent them being pushed or blown over. There are two usual methods for doing this: one is to use stakes (e.g. garden cane or sticks); the other method is to use tent pegs (use at least three per cage at equally spaced distances; so if you're using three, anchor at 12 o'clock, 4 o'clock and 8 o'clock).
It is important to remember that cages can help other animals as well as hinder rabbits. If you're using slug protection, you will probably need to protect the cage as well as the plant, as slugs are quite capable of climbing the cages and then getting on to the leaves, thus dodging any protection which might only be around the plant's stem.
Deer constitute a much greater hazard than might be thought; many crops have been lost to them, but there are a number of deterrents available to the guerrilla gardener.
Unlike domesticated or agricultural animals, deer (quite rightly) don't trust the presence of humans and attempt to keep as large a distance as possible between themselves and any possible contact. This can be used against them.
The scent of human urine is very off-putting to deer and they will try to avoid it as it is a sign of human presence. Before going to your grow site, drink larger-than-usual quantities of water and give the area a good sprinkling while you are there. Avoid urinating directly on the plants themselves. Some people fill up a two-litre bottle and take that with them. Urine scent will evaporate over time and can be washed away by rain so levels will have to be maintained periodically across a grow.
Extrapolating on the previous idea is the idea that deer will avoid other large predators as well as humans. Some zoos sell big cat excrement (that's crap, to you and me) as a fertilizer / natural manure. If you're lucky enough to live near a zoo, big cat crap is as good a deer deterrent as you could want, although, like urine, it might need topping-up every so often. There is also a cat deterrent on the market called "Silent Roar", which is a mixture of lion excrement and other chemicals; this is also apparently effective against deer, but also requires occasional topping-up.
Any unnatural or humanistic scent will make deer think twice. Some growers use soap to provide that scent. If using soap, you should be careful to keep it away from the plants themselves, as it could prove toxic if it soaks into the ground near the root system. Some growers hang soap from stakes or trees in the vicinity. If using soap, make sure it's as smelly as possible, but also try and pick as natural a colour as possible; flouroescent pink can be noticed from quite some distance away.
Some growers use fishing line strung from trees at chest height to deter deer. The idea is that the deer walk up against the line and register it as an unnatural pressure (the line being largely invisible) and thus decide to keep away. Fishing line can draw attention as well as deter deer, so use this method only when the circumstances call for it.
Sheep, Cows and Horses
Move the grow site. Seriously. There is no effective deterrent against farm animals except for avoidance. These animals do not fear humans, are herbivorous, are strong, are protected by property law (that's a shorthand for saying that it's illegal for you to kill them, aside from it being morally wrong anyway) and are voracious eaters. Move the grow or think again.
You're growing outdoors. You're not going to avoid insects. There are various methods for dealing with insect pests which are outlined in the Pest Control section of the Grow FAQ, but generally, unless it becomes a specific and persistent problem, it's better to accept them as a fact of life. Many of the repellents, such as those based on Neem oil, are impractical for the guerrilla gardener as they are based on the premise of "regular application", with "regular" meaning "weekly, or even more frequently", thus running counter to the stealth philosophy.
As a general bug repellent, Nitramkram offers this solution:
1 tablespoon of vegetable oil
One teaspoon of liquid soap
One litre of water
Combine the garlic and vegetable oil and leave to soak overnight. Strain and add to the litre of water along with the liquid soap. Spray regularly. Garlic is known for its antifungal and antibacterial properties, but it is its insect repellent qualities that most gardeners like.
Aside from all the solutions above, which have intentionally been geared towards general-purpose usage (preferably without detrimentally affecting the grow spot), your local garden centre will doubtless have plenty of shiny products it will only be too keen to sell you. Some may be brilliant, some may not, but think carefully about using them before you do. Remember, we're in the stealth business. Anything which requires regular application requiring frequent grow visits, or is geared towards non-consumable foliage (e.g. roses) may not be the best stuff to be putting on your MJ.
Thanks to all the people who've discussed these issues at length in the forums over the years.
This post has been edited by Bish: 30 June 2007 - 02:05 PM