I found this chapter comprehensive and interesting in terms of integrating the questions of site preparation. It's very different to the process of preparing the ground for a conventional garden, although there is some overlap. It's certainly useful for getting you thinking. The only thing it really lacks is the point that the practicalities of site preparation may require modification to your existing plan, and I think you need to be aware of this.
Okay, you have a plan, and you have a design. The next thing to do before you start planting is to prepare the ground.
Most farmers want uniform soil. Most forest gardeners want a mix of soils in order to meet the demands of a range of habitats. Changing the soil is a designed disturbance, and therefore a design problem, subject to similar design processes as those discussed in the previous two chapters. The aim of this chapter is to give you the information required to make sensible choices on the subject. Site preparation directly affects the subsequent successional pathway.
First you need to clarify your site preparation goals and objectives. This will be guided by your existing site assessment and the goals articulated in the design process described in the previous chapters.
I've seen images and video (some of it on here) that suggests people have not been taking site preparation seriously. Just planting fruittrees on a previously unmanaged grassland will not achieve the same results as planting those same trees on a properly prepared site, and I think this is one reason for failure. This chapter discusses what legacies would be expected from proper preparation.
Once you have worked out your goals and objectives, you can then move on to working out which techniques will be most appropriate. Do you need to cover crop, amend or mulch, for example? Can you apply these techniques while preparing plants in pots ready to plant out? What affect will this have on your budget while yields are relatively poor? Remember that each technique can serve multiple functions. The authors advocate a one-year planting delay in order to control some opportunist species that will become a problem later. This is something that has already given me pause in my plans, and I think I have a possible solution I'd need to discuss with a potential partner moving forward.
The chapter then spends a great deal of time discussing a Rogue's Gallery of Challenging Site Conditions.
Top of this list is Climate. The authors make important points about matters such as frost (which, remember, some fruit trees need, but not at the wrong time), but in the relatively few years since this book was published the question of climate has become a more pressing one, with increasing clarity over just how quickly climate disruption is going to affect agriculture, and it's now clear that a forest gardener thinking in decade-long terms is going to need to be prepared for this. As I write this I receive an email from the British Trust for Ornithology entitled “Summer visitors here to stay?”. What is happening in terms of bird migration is mirrored by effects on vegetation. Meanwhile, I'm increasingly sure that Scotland is going to be the wrong place for my own forest garden, for a range of reasons. I think there is a strong case for considering climate if you are going to have to relocate anyway. Planning for resilience against a range of conditions, from drought to flood to strong winds is definitely in order. Actually, I find it interesting that I'm considering becoming a climate refugee from somewhere I'd hoped would be relatively stable, but that nasty temperature differential between warm water coming out of the Gulf of Mexico and the cold water in the North Atlantic as a result of the melting of the Greenland Ice Sheet, which has already been implicated in the recent storms hitting the island, really gives me the willies. This is the kind of thing that causes flooding, waterlogging, inadequate ripening days and general crop failure. Scary stuff!
Then there is the question of landform: a steep slope erodes easily, which a flat surface may become waterlogged. Swales or check logs may be useful for the first; raised beds, mound planting, or even drainage may be useful for the latter.
Soil may be compacted, have restricted layers (such as subsurface hardpan), abrupt soil texture boundaries, may have an extreme soil texture, such as clay or silt, and may have a low water percolation rate, several of which may be related to the question of poor surface drainage.
High water tables may kill plants, and your soil pH may be too low or too high, both of which restrict nutrient uptake. Salinity is a major problem in many soils, especially those that have been excessively irrigated. Worse yet is the problem of heavy metal contamination: either of these latter two should give you pause in terms of even buying land in the first place. Infertility and nutrient imbalance is a threat to agriculture as a whole, not helped by the insistence of many farmers, a tendency that continues today, that the only added nutrients that plants require are nitrogen, phosphorus and potassium. The authors seem to avoid being critical over this, but I think they should have been.
Soil biology imbalances present other problems. In a forest garden the soil biology will move from the bacterial-dominated biology of most grassland and forb habitats to a fungal-dominated biology of woodland. This process can be helped along by the gardener.
Finally, you have the problem of unwanted vegetation. This may take the form of highly competitive species or rhizomatous ones, which will present a weed problem within a year or two.
It sounds like a lot to worry about, but many of these problems will not apply to any given site.
A useful table presents questions of relevant features and possible remediation strategies. Note that there are mistakes to be made or avoided here.
This chapter then moves on to aHero's Gallery of Site-Preparation Strategies and Techniques.
The point here is not a simple silver-bullet approach. The techniques are presented in no particular (well, more or less alphabetical) order.
Specific soil amendments are, of course, covered in detail in many sources, but the authors advise against the use of chemical fertilisers, preferring the use of things like rock dust and organic matter. Before adding any amendment, you need to conduct proper soil testing.
For heavy earth moving the backhoe can be of use. I've been reluctant to use anything I can't shift using my own muscle power, but I can see there can be a case for their use: even these authors treat it as a last resort, and give careful advice for the conditions under which they should be used.
Check logs are particularly useful on sloping sites where you have wood to play with. These slow erosion and help add nutrient to the soil, while providing a substrate for mushrooms.
Most users will know about composts and compost teas, but the forest gardener needs to know how different types of composts, dominated by either bacteria or fungi, can assist with early and late-succession plants. The use of compost plugs may give plants a good head start, with a supportive soil biology.
The authors provide references for cover crops, including green and brown manuring and rolling and permanent (which would include edibles) cover crops. If cut at the right time, it's possible to encourage beneficial insects into trees to control pests. I like this idea.
More radically, for broadscale projects, deep ripping (chisel ploughing) can break up subsoil. This is really only suited for a large, compacted site.
On the other hand, double-digging is familiar to most gardeners. It seems contrary to principles of minimal tilling, but this can substantially increase yields (although I wonder if this is short or long term, simply making nutrient more biologically available over the short term: research is needed), and is likely to be a one-off in a forest garden. This is also suited to a compacted site, but one on a smaller scale.
I despise herbicides, includinghot water, flames and chemicals as much as the next permie, but the authors do give it a mention. The problem, as they point out, is the reflexive, unthinking use of herbicides. There can be a case for the planned and considered use of hot water, flames, and even organic and inorganic herbicides. They discuss the use of these things, but note care and forethought is required. There is actually quite a long section on this, given that the authors seem to feel the need to explain its inclusion as part of a more comprehensive weed-management system, especially when dealing with particularly opportunistic species such as Japanese knotweed (Reynoutria japonica). They admit there are risks, and are clear this is something to be used infrequently, if at all.
Having got this dirty subject out of the way they move on to infiltration swales. Given that other authors (notably Mollison) cover this subject, they actually go into it in some detail. It is possible to create a swale in the wrong place, or even on the wrong type of land, and it's more than possible to muck it up, but it's clear this can be an important aspect of your water-management strategy.
Another important aspect of water management is irrigation. This is beyond the scope of this book. Irrigation systems can be expensive, especially when pump fed, but the use of gravity-fed systems and hydraulic ram pumps are also feasible. I'm aware of systems using bamboo to carry water from streams (http://cseindia.org/node/2839) and, of course, bamboo is a plant worth considering in any forest garden, given its many uses.
This book helped me think further about the advantages of pits and mounds, a subject which would include hugelkulture, which enable you to create microclimates for different species. In the past I've used these primarily for the planting of annuals, but they can be used effectively for perennials as well.
There is a useful discussion about the advantages and forms of mulch. One table is probably only of use to permies working in the area the authors are familiar with, dealing with leaf litter from their localnative trees, but another gives carbon, nitrogen, phosphate and potassium ratios for a number of relatively readily available organic materials. There is a whole feature article on mulch, its advantages, challenges and solutions. The problem is that nutrient losses can be significant even years after a disturbance in a rapidly succeeding forest ecosystem, and these nutrients need to be replaced. Remember to grow mushrooms in your mulch.
Mycorrhizal fungi are an important aspect of a forest garden ecosystem, but not all mycorrhizal fungi suit all plants. There is a useful table here discussing what types of plants suit what types of fungi. Most sites shouldn't need it, but many sites can benefit, and it's well worth analysing which inoculants could be useful. I hope to be able to move on from this at some stage and learn to inoculate with edible fungi. It's certainly worth addressing this question with more detailed sources, such as Mycelium Running, by Paul Stamets, and The Mushroom Cultivator by the same author.
There is a brief description of the penetration of restrictive layers, where an impervious layer of soil is sandwiched between two permeable ones. Again, this will only be relevant on some sites.
Then there are two paragraphs on prescribed burning, which is an old woodland management practice, and some forest habitats are dependent on it, but this is not the kind of thing you want to do without the experts on hand to tell you what you need to do and how to do it safely.
There is an interesting discussion on radial trenching and radial raised beds, used to improve tree root growth on compacted and impermeable soils. This takes less effort than double-digging or chisel ploughing.
Radial trenching can incorporate raised beds, familiar to many gardeners and with any number of advantages. With careful forethought these can incorporate other features which may help with watering, for example. Again, this overlaps into the field of hugelkultur, which is not discussed.
In some circumstances you may wish to install rhizome barriers. I've already mentioned bamboo, of which many species require a rhizome barrier in order to prevent them getting out of control. If you want to grow bamboo, for which there is a strong case, you need to work out whether the place you want to put it is the best place for such a barrier.
Soil inoculation is related to mycorrhizal inoculation and may include it, but this involves taking healthy soil from a site with and existing biological community and mixing it with poorer soil on your site. You run the risk of introducing pathogens, but this should be outweighed by the bacteria and fungi you introduce with your soil and duff. It does need to be done carefully and with forethought, if nothing else to minimise damage to the donor site.
Soil stakes are used to increase infiltration and aeration, loosen the soil and improve fungal biomass. They are a good way of using up unwanted wood.
If you have a high water table you may wish to install a subsurface drainage system. This is likely to be expensive and time-consuming, but will discourage root rot.
Finally, you may need to remove woody weeds. My own preference in such matters is to use fungi as decomposers, but this is sometimes not viable or appropriate. These authors recommend the use of heavy tools, followed by chipping (which you can add to your mulch pile).
This is another field I could find myself getting excited about, if frustrated on occasion. It's the kind of thing that requires you to hold substantial amounts of information in your head in order to reach an optimal solution. The fun bit will involve working out which mix of strategies to use in order to arrive at an optimum solution. By comparison with some of the design features already discussed this would be a relatively simple process, but one you need to get right.