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Chop and Drop Plants

Plants that produce biomass relatively quickly, and/or which are good at accumulating particular nutrients, can be considered plants to chop and drop. Chopping and dropping helps to shortcut nature’s cycles and return the nutrients contained within the plants to the soil, where they can be taken up by other plants growing nearby. At least once a year, and often more frequently, these chop-and-drop plants can be cut, and the plant matter can be left to decompose on the surface of the soil.

The Ultimate Guide To Chop and Drop

Once you begin to learn a little about permaculture and organic growing systems that work with nature rather than fighting it, you are sure to hear the term 'chop and drop'.

If you are unfamiliar with this term, read on to learn more about what this means, why we chop and drop in permaculture systems, which plants we might chop and drop, when it is best to do so,

What Do We Mean By Chop and Drop?

Chop and drop is term which neatly and simply sums up the process itself. It refers to the cutting or pruning of plant material that is then simply dropped onto the soil and used as a mulch.

This is a practice that might be employed within perennial growing systems, such as forest gardens, or within areas of annual cultivation.

Why Chop and Drop in a Permaculture System?

An understanding of nature's cycles is key to understanding this permaculture practice.

In nature, there is a natural plant cycle of growth from seed, decay, death, decomposition and new growth. In a natural system, as leaves fall and plant matter dies back, the nutrients that the plants contain are returned to the soil, to allow the cycle to begin anew.

Chop and drop systems are simply a way to shortcut this natural cycle, and to make sure that fertility and soil health are maintained in a cultivated area – on a farm or in a garden.

Chopping and dropping plant materials as mulches in permaculture systems is a crucial way in which we mimic and work with nature to achieve our aims in a conscientious, ethical and sustainable way.

What Should We Chop and Drop?

When we talk about chopping and dropping in permaculture, often we are talking about chopping and dropping species that will aid us in maintaining fertility within a growing area and in protecting and improving the soil.

Within this category of chop and drop plants there are three key groups – nitrogen fixers, dynamic accumulators and biomass plants that grow quickly and generate large amounts of organic matter. Some plants will fall into more than one, or even all of these groups.

Nitrogen Fixers

The first group of chop and drop plant to look at are those plants known as nitrogen fixers. These are plants which have symbiotic relationships with bacteria in their root nodules that have the capacity to take atmospheric nitrogen and make it available in the soil.

Nitrogen is abundant in out atmosphere, but in gardens and growing systems it can become depleted from the soil as it is utilised by the plants.

Since nitrogen, along with phosphorus and potassium, is a key plant nutrient – essential for healthy plant growth – ensuring the presence of sufficient nitrogen in the soil and plants is important for the health of an ecosystem.

When nitrogen fixing plants are chopped and dropped, the nitrogen contained within these plants returns to the soil, where it can be taken up by other plants growing nearby.

Dynamic Accumulators

Another key group of plants to think about in chop and drop systems are those often loosely referred to as 'dynamic accumulators'.

Often, in permaculture, when people speak of dynamic accumulators, they are referring to plants with deep roots that have the ability to draw up nutrients from deeper levels of the soil that other plants within an ecosystem or growing area cannot reach. (Comfrey is one well-known permaculture plant within this category.)

Plants differ in their capacity to gather and store certain plant nutrients. Some are able to absorb and store higher levels of certain nutrients in their plant tissues than others.

Interestingly, this is an area where research is ongoing. The properties of many plants in this regard have yet to be fully explored. And the term 'dynamic accumulator' is not always clearly defined in scientific terms.

However, research evidence is growing that strongly suggests that certain plants that are good at gathering and storing nutrients can be particularly beneficial for use as mulches within a chop and drop or sheet-mulching system.

Quick-Growing Biomass Plant Species

Another group of plants that can be extremely useful in maintaining fertility and soil health in a system are biomass plants – those which, though they may not always be nitrogen fixers or dynamic accumulators, quickly generate larger quantities of organic matter.

Quick-growing species can provide prodigious amounts of plant material which, when chopped, can be laid as a mulch of organic matter to cover larger areas.

As permaculture practitioners will know, protecting and improving the soil is crucial in any growing system. And by growing some biomass plants, we can ensure that we have the mulch required for sheet-mulching/ no dig gardening without the necessity of importing materials from outside the system itself.

Laying mulches of any organic material (carefully chosen for a specific site to meet the needs of the soil and other plants growing close by) can help not only to maintain fertility but also to improve soil structure, retain moisture, suppress weeds and prevent soil issues such as runoff, erosion and compaction.

Of course, which plants fall into these three groups and be useful for chop and drop systems depends on where you are located and the specific conditions where you live.

Above and beyond these three key groups, however, there are also other plants that it can be beneficial to chop and them simply drop to mulch down and compost in place. In fact, it can be beneficial to shortcut natural cycles and chop many different plants to break down in situ and return nutrients to the soil.

Chop and Drop in Annual food Cultivation

For example, we might simply chop and drop crops in our vegetable gardens, rather than removing annuals at the end of the season to compost them elsewhere.

We might also chop and drop some weeds on the surface of the soil where they grow, rather than weeding them out and removing them entirely from a given area.

Chop and drop in annual food production is often also used in the context of cover crops, or green manures.

Certain plants are used (often over the winter in cooler climate zones) to cover and protect the soil in annual growing areas over the winter months. Cover crops might also be used to fill gaps in a planting and harvesting schedule and to make sure that there is a living root in the soil over as much of the year as possible.

Cover crops and green manures have specific properties and can add different things when chopped and dropped. It is important to understand the different properties of different cover crops and green manures in order to understand which might be best for use in a specific chop and drop system.

In some cases, there are important things to note. Such as, for example, that certain brassicas used as green manures can impede the germination of certain seeds sown in an area as the plant materials break down. This is just one example...

When choosing chop and drop plants to use as a green manure or cover crop, it is also important to think about things like crop rotation.

Tree-Based Chop and Drop Systems

Woody material from trees and shrubs can also be employed as a mulch material in chop and drop systems.

However, it is important to understand the conditions where you live, since woody material will break down much more quickly in some environments than it does in others.

In the tropics, and many hot and warm climate zones, woody materials can break down quickly. In cooler and drier zones, however, wood often breaks down much more slowly.

So in order to derive the same benefits, in some areas it will be beneficial to take pruned materials and chop it up more finely, or shred it, before you use it as a mulch.

In the maintenance of my own growing systems, particularly in my forest garden, woody organic matter is crucial in mulching and ongoing fertility. But I use a garden shredder to obtain wood chip that I can use as a mulch, breaking up some of the material into smaller pieces that will break down more quickly and easily.

I use ramial (branch tip) wood cuttings and other shredded garden prunings to help create a fungal-dominant soil that is useful for the cultivation of trees and shrubs.

Making sure that a woodland, forest or food forest system has a fungal-dominant rather than bacteria dominant soil can help in creating and maintaining a functioning ecosystem.

One reason that wood chip can be good to use around trees and woody shrubs  is that it helps to nurture a fungal environment – like that of a natural woodland or forest, where there is typically a fungi-bacteria ratio of 10:1 – 50:1.

Whenever wood chips or other woody materials are used in a chop and drop system, it is important to remember certain things, however:

The Type of Wood Matters

When chopping and using woody material as mulch, you not only have to think about the size of the pieces and how long they will take to break down where you live, but also which type of wood you are dealing with.

Remember that some woods like conifers can acidify conditions to a degree. And certain woods, like walnuts, contain allelopathic chemicals (juglone in the case of walnuts) that can affect the growth of other plants.

Soil Nitrogen Can Be Affected

As woody material breaks down, nitrogen is sequestered by microorganisms involved in the process. Since the material itself is not high in nitrogen, these microorganisms can lead to depletion of nitrogen (temporarily) from the surrounding soil.

Depletion of nitrogen short-term as the materials break down is one reason that while it is beneficial to place wood chips or woody material as mulch in tree-based systems, it may not always be the best idea in an annual area such as a vegetable bed.

But you can counteract this period of nitrogen depletion by layering wood chop with nitrogen-rich chopped and dropped plant materials. When you do this, there will still be plenty of nitrogen to go round even while the decomposition is taking place.

(Green wood with some foliage passed through a garden shredder will already have this nitrogen rich material built-in.)

Often plants belong in more than one of these categories. But understanding the properties of specific plants can help us work out when and where a chop and drop approach can be beneficial.

When To Chop and Drop Plant Materials as Mulch

When it is the best time to chop and drop plant materials as mulch very much depends on your location, which plants are being used, and your goals.

But some key things to consider are:

  • Rainfall and moisture levels.
  • Chopping and dropping before plants go to seed.
  • Optimal cutting back or pruning times for specific plants.
  • The timetable in an annual garden.
  • Disease and pests.

Rainfall and Moisture Levels

For the effective decomposition of mulch materials, a general rule to remember is that a chop and drop should typically be carried out when precipitation exceeds evaporation. (Wetter times, when rainfall is sufficient.)

For me, here in Scotland, and for others in many temperate climates, that means in early spring or in autumn (fall).

However, since in my location, rainfall is moderate through much of the year, I can also chop and drop through summer, while this may not be the best time for this activity in areas where summers are much drier.

One example of a time when one might chop and drop in summer (where rainfall is sufficient) is when a quick-growing plant can be chopped down more than once over the growing season, to regrow and be chopped and once more later in the season.

Comfrey, for example, is a plant that I can chop and drop two or perhaps even three times over the course of the growing season to use as mulch.

Chopping and Dropping Before Plants Go To Seed

While it is important to think about precipitation and water availability when deciding when to chop and drop, there are other considerations.

For example, you might want to think about when it is best to chop and drop before a plant goes to seed. (With some weeds, for example.)

Optimal Cutting Back or Pruning Times for Specific Plants

The best time to cut back or prune a specific plant might also dictate when best to chop and drop its plant material to ensure that it will live to be chopped and dropped again in subsequent years.

The Timetable in an Annual Garden

In annual growing areas, when you chop and drop might also be dictated by your sowing, growing and harvesting schedule.

Disease and Pests

Another consideration when deciding when to chop and drop is disease control. Of course, we need to avoid spreading disease, and should not chop and drop when materials show signs of infection.

We might also, depending on location, have to think about certain pests. For example, where I live, voles and other rodents can sometimes become an issue when thick mulches are laid over the soil in annual areas over winter, so this is something to bear in mind.

Chop and drop strategies can be extremely useful in many permaculture growing systems. But employing this strategy with the right plants, at the right times, is crucial to achieving the best resu