5 Ways to Prepare Beds for Tree & Shrub Planting

Paul Alfrey - Balkan Ecology Project

Wednesday, 19th July 2017

Five methods for creating beds for trees and shrubs. From straw bales and mulching to green manures and inverted sod.

During this post we will be looking at various ways to prepare beds for planting, specifically for planting trees and shrubs. I'll introduce you to a trial we started this spring where we're looking at 5 different bed preparation methods to see which method works best. We'll go through how to implement each method, why they are useful and finally look at the criteria we are judging the effectiveness of each method by. We'll start with an introduction to the trial garden where we are undertaking this comparative study.

In April 2017 we began the development of our new trial garden (Ataraxia). The garden will be used for a range of perennial polyculture trials and experiments in order to discover the best practices to produce nutritious affordable food while enhancing biodiversity.

The first of our trials begins with the development of the planting zones. We want to discover what is the best method to establish a planting bed for the perennial plants such as fruit trees and shrubs and perennial vegetables. The aim of the trial is to discover methods that are inexpensive, time efficient, least disruptive to the existing wildlife and that provide the optimal conditions for the incoming plants.

When planting trees and shrubs into grassland or fields previously used for agriculture, I prefer to prepare the area at least 6 months ahead of planting, 12 months is even better. We often prepare the planting zones in early spring for late Autumn planting. I call this "advance planting preparation".

Advance Planting Preparations - (APP)

What is it? It's basically the addition of organic matter into the planting zone 6-12 months before planting to improve soil conditions for the incoming plants. This can be in the form of mulches that suppress existing growth and decompose in situ or in the form of green manures that replace the existing growth and improve the soil.

Why do it?

The benefits for advance planting preparations include the following:

Mulches - It's generally acknowledged that early succession plants such as grass and forb prefer bacterial dominated soils whereas trees and shrubs prefer fungal. By preparing soils in advance of planting you can alter soil conditions to that which trees and shrubs are more accustomed to. A great way of shifting the soil ecology from bacterial to fungal is to deep mulch the planting zone with high carbon material such as wood chip (preferably ramial wood chip) or with straw at least 6-12 months before planting. If you live in urban areas, ramial wood chip should be very easy to get hold of from your local tree surgeon (often free of charge). In rural areas, straw should be available and spoiled straw that has been exposed to the rain during winter is often freely available as it cannot be used for animal bedding.

^{Wood chip - The smaller diameter the source wood is, and the more green material in the chip, the faster it will decompose. Chip from small diameter source wood is called ramial wood chip and is the best material to use for mulch in APP. Photo credit David Domoney}

Mulches - Grass can compete vigorously with trees and shrubs for nutrients and water. The application of heavy mulches reduces or in some cases eliminates the existing vegetation without the need of heavy digging work or the use of tractors and machinery. The vegetation that is suppressed by the mulch decomposes along with the mulch and adds to the fertility of the soil and improves soil structure.

Mulches - You can reduce the expense of time preparing compost or the cost of purchasing it by using fresh manure or other fresh organic matter layered as sheet mulch. Doing so 6-12 months ahead of planting allows enough time for the material to decompose in situ to levels that are not harmful to plants.

Mulches - The mulch provides good habitat for a range of invertebrates many of which are beneficial in our garden ecosystems. Slugs and snails will also shelter in the mulch and this often attracts slow worms, toads, frogs and lizards that feed on them under the safety of the cover. Ground beetles and a range of spiders will also make home in the mulch and perhaps the most beneficial of all the soil dwelling organisms, earthworms, will settle and multiply under the mulch slowly bringing the material down into the soil improving structure and creating some of the best plant fertiliser around, vermi-compost.

Green manures - Can improve the soil fertility, relieve compaction, improve the soil structure providing better drainage and water retention, suppress weeds and attract beneficial insects and pest predators.

^{An excellent green manure - Sainfoin - Onobrychis viciifolia}

Some considerations

You need to apply large quantities of mulch and manures and for large areas this will often mean importing from offsite. If you can tap into local waste streams (as mentioned above) this is fine but it some places it can be expensive to purchase and transport these materials.

Plants that grow via rhizomes and runners such as brambles and couch grass may grow through or around the sheet mulches and green manure cover. This can be overcome by removing these plants before mulching, or spot weeding as they reappear. If the area is dominated by pernicious weeds it's probably best to take the time of removing them before mulching.

On heavy clay (especially compacted clay) applying organic matter to the surface (mulching) is not very effective as the clay layer forms a barrier or "pan" that is restrictive to the plant roots and the organic matter is not easily naturally incorporated into the clay. In these cases it's necessary to incorporate the organic matter into the soil via double digging or deep ploughing the area, adding the organic matter and then rotary tilling. The initial work is intensive but following this applying organic matter to the surface will work (so long as the area is not compacted again).

On any compacted soils it's worth breaking the compaction and relieving any pan that may be present before mulching.

It's necessary to prepare a seed bed when using green manures and this often entails ploughing and tilling the area for large areas or digging over and raking for small areas.

Always apply a mulch following periods of heavy rain or water the area well beforehand to ensure the soil is well soaked. This will activate the microbiology in the soil that play a critical role in the decomposition process.

So now let's take a look at how to set up the beds and how to implement the various methods of advance planting preparations we are trying out.

Setting up the Beds

The position of the beds on the site were dictated by the aspect and topography of the land i.e. we wanted to position the beds to receive as much sunlight as possible (west - east axis in our northern hemisphere) and to utilise the natural slope of the land to assist with irrigation. We laid out the beds on an area that was more or less on contour so we could flood irrigate from the stream water that can be diverted into our site from the NW. We also selected the planting location slightly lower then the proposed location of a pond so we may irrigate from the pond if the stream water is unavailable.

Digital terrain models such as above (see original post) are great for selecting locations and planning. Once we are ready with our design we carry out a ground topography survey to physically peg out contour lines and positions of the design elements on the site.

A benchmark contour line at the high end of the site is marked as the position for the first bed and we offset from that line at regular intervals to ensure we have regular sized beds and paths. I like to use regular size beds and pathways for our trials so that they can be replicated easily and perhaps more importantly they suit the modular basis of our designs and allow us to scale up and down our designs easily.

We then peg out the top corner of the first bed and measure down to the edge of the east side of the beds marking 1.5m wide beds, 50cm internal pathways and 1m external pathways (to allow easy turning for the mower).The length of each bed in this case is 25m. For beds any longer than this it's probably a good idea to make lateral access so movement within the garden is easy.

Once we have the location of the beds worked out the next step is to clear the bed and pathway area from shrubs and young trees.

^{Digging out the shrubs and saplings from the area and piling the material on the perimeter of the area.}

The removed vegetation is piled onto the edge of the garden to serve as shelter to lizards and other wildlife seeking refuge from birds and other predators. The lizards quickly made use of the cover.

We attached string to the side of the pegs which clearly indicate the footprint of the beds and paths. Before going any further I tried the lawnmower within the pathways to test how comfortable it is at turning corners at the ends of the beds. 1m wide external paths make for easy turning of the corners with a standard 45-50 cm wide lawn mower.

^{Beds pegged out and defined with string. The mini digger in the background is digging out the pond at the highest point of the site.}

Ataraxia%2B-%2BPath%2Band%2BBed%2BDimens

With the six beds clearly defined we now set about implementing the advance planting preparations for each bed.

Our five methods for advance planting preparations

1. Inverted Sod and Mulch - (Soil - Straw)
2. Green Manure - (Plough - Till - Sow White Clover - Sainfoin and Marigolds)
3. Dig over and Sheet Mulch - (Card - Manure - Straw)
4. Sheet Mulch - (Card - Manure - Straw)
5. Straw Mulch (Straw)

All of these methods are best implemented when the soil is moist, for example, following heavy rains when the soil profile is thoroughly soaked but has had enough time to drain i.e not water logged.

1. Inverted Sod

Method one entails slashing the existing vegetation to ground level and leaving it on the surface. A layer of inverted sod is then applied to cover the surface of the bed. In some cases you may wish to dig out the top soil from the pathways and this can be inverted on to the bed area. In this case we wished to leave the pathways grassed and used top soil removed from a pond excavation on site. Following the top soil a layer of straw mulch is applied approx 10-20cm deep.

^{Inverted Sod applied to surface. This is followed by a layer of straw.}

2. Green Manure

Method two removes the existing vegetation and replaces it with plants that can improve the soil for the incoming plants. For example on sites with low fertility soils, nitrogen fixing green manures are a great way to lift Nitrogen (N) to appropriate levels. The green manures can also add significant quantities of organic matter to the soil improving structure and drainage and can serve the needs of beneficial insects.

To boost the organic matter content of the soils, the green manure should be cut at regular intervals and plowed into the soil or covered with a straw mulch before planting occurs. In such cases the green manure used should be a fast growing annual cover. An alternative is to sow a perennial cover, cut back at regular intervals (once established) and plant the crops directly into the living mulch.

We sowed the following seeds onto the prepared bed on the 18th May.

Trifolium repens - White Clover 200g - Perennial

Tagetes patula 100g - Annual

Onobrychis viciifolia - Sainfoin 100g - Perennial

We'll probably need to irrigate this bed from July onward for a good cover to establish and we'll cut the vegetation in late summer and decide whether to mulch before planting in the Autumn or plant directly into the mulch based on the performance of the cover.

To prepare for sowing we ploughed and rotary tilled the area to provide a good seed bed.

We then hand sowed the seed onto the surface before a rainy period was forecast.

The use of cover crops to prepare beds for perennial polycultures is something we'll be experimenting more with in the future.

3. Fork Over and Sheet Mulch

Method three entails slashing the existing vegetation to ground level, forking over the surface of the beds and then placing a card/cloth layer to cover the soil surface and a layer of manure on top of the card/cloth. We used approx 30 L of manure per m2 and finally topped this with a 10-20cm layer of straw.

^{Digging over the bed, placing a layer of card and cloth, adding 30L of manure and covering with 15-20 cm layer of straw.}

4. Sheet Mulch - Cardboard layer, manure layer, straw layer

Method 4 is the same as above but without forking over the beds.

5. Straw Bales

Method five is quite simply slashing the existing vegetation to ground level and applying a 20cm layer of straw to the surface. A simpler way is to place a straw bale on the location where each tree will be planted and this works really well if you are only planting a tree layer, however for these beds we intend to plant out 4 layers; trees, shrubs, perennial vegetables and bulbs so it makes more sense to mulch the entire area.

^{Placing bales on the planting locations of the trees clears the weeds from the planting zone, encourages a fungal population of soil microbes and within 6 - 12 months the surface of the bale at ground level will decompose providing a light layer of compost for the newly planted tree/shrub.}

The Pathways

The pathways are left undisturbed and the grass cover is mown at regular intervals throughout the growing season and can be applied as mulch (as long as it's not full of ripe seed). We allow 1m wide access at the end of beds to allow easy turning with the mower.

In some cases we have removed 10-15cm of soil from the paths and applied this to the bed surface and then sowed the paths with a perennial cover such as White clover - Trifolium repens, but in this case we wanted to keep the grass cover as it makes a good durable surface and can provide a regular supply of trimmings for mulch when we mow throughout the year.

^{The perennial polyculture trial beds - 6 beds - 1.5m wide and 25m long with 50cm internal pathways and 1m wide periphery pathways.}

How we are measuring the effectiveness of each method

As mentioned above, the aim of the trial is to discover methods that are inexpensive, time efficient, least disruptive to the existing wildlife and that provide the optimal conditions for the incoming plants.

The criteria we are judging the effectiveness of the methods and how we will measure effectiveness is as follows:

The smallest amount of effort for the greatest benefit i.e in labour, materials. - Record of Inputs
The least expensive method (without sacrificing quality) - Cost Analysis
The least disturbance to the existing ecosystem - Entomology Survey
Mineral analysis compared to base sample - Mineral Analysis
Physical analysis compared to base sample - Soil Test Card
The beds should provide great soil conditions for the incoming plants i.e, free from competitive neighboring plants, good structure, moist and fertile, free draining. - Observational Report

Will be publishing the results of our trials in the winter.

What will we be planting in the beds

I'll write about the planting schemes for these beds in more detail in a future post but here's a quick overview of our planting plan for the beds.

Beds 1, 3 and 6 are designated as biomass beds and will be planted out with pioneer species of nitrogen fixing trees to supply biomass to the productive beds 2, 4 and 5. The productive beds will consist of 4 vegetative layers of productive and supportive plants. Mainly fruit and nut crops in the upper canopy, a lower canopy/shrub layer of fruiting shrubs. a herb layer perennial vegetables and a ground layer of bulbs.

While light is abundant in the early stages of the garden development, the goal is to use the biomass beds 1,3 and 6 to supply biomass to the productive beds via chop and drop pruning and fast coppicing practices. As the system matures the productive beds will overshadow the biomass beds at which point they will be replaced with shade tolerant productive crops and support species.