Hügelkultur in the Orchard Nursery

Last year, I grafted twenty apple scions onto dwarfing rootstock – all russet varieties, for a new cordon section on the allotment – and planted the brand new trees in a mature Hügelkultur bed, to grow on for their first year. I was quite impressed with the results, and it got me thinking about the practical applications and potential benefits of the Hügelkultur system in an orchard nursery setting.

If you’re just looking for a quick summary of my thoughts on the subject, please feel free to skip ahead to the conclusions. Otherwise, let’s start with the basics.

What is Hügelkultur?

The Wikipedia entry on Hügelkultur offers a good, comprehensive overview of the subject, so I’ll just stick to a quick summary.

At its simplest, Hügelkultur – a German term meaning ‘mound culture’ or ‘mound growing’ – involves making a tall, frameless raised bed of organic matter: logs, sticks or twigs, leaves, soil and mulch.

The best time to construct a Hügelkultur bed is in the autumn. First dig a shallow trench – you can skip this stage if you follow a 100% no-dig methodology – and line the base of it with branches and logs. Smaller woody stems, twigs and sticks are added on top of the logs, then a layer of grass turf, then a thick layer of dead leaves or leaf mould. The mound is topped off with soil and then a final mulch layer can be added to help prevent rapid soil erosion.¹Over on my old allotmentnotes.com blog I posted an article on building a Hugelkultur bed (the very same one that we’re talking about here, as it happens), if you’d like to read a bit more about the process I followed.

Here’s another pic of the Hügelkultur bed shown at the top of this post, this time shown mid-way through construction back in February 2019²Not an autumn build, I know, but I’d only just learned about the method, had a lot of woody prunings to get rid of, and didn’t want to wait all year to get started.. At this point I’ve reached the ‘twigs and sticks’ stage and just need to add layers of leaves, soil and mulch:

In some diagrams a finished Hügelkultur mound appears to be quite tall, steep-sided and with a curved top, but I’ve found a more useful way to build them is wider at the base and flat-topped. This helps to retain water from rain or irrigation and avoid excessive soil erosion.

The finished Hügelkultur mound should be left to mature over the winter – or for the next few weeks, at leas – to allow the material in the bed to settle, and decomposition to set it. In spring, suitable crops are then planted directly into the mound; their initial root depth usually placing them into the soil layer.

Nutrients will be gradually released into the soil of the Hügelkultur mound over a period of time, as the leaves and woody matter at the bottom of the bed will decompose at different rates. Eventually the whole bed will become, in effect, one big compost heap. This can take around five to six years, depending on the size and thickness of the logs at the base of the mound. At this point, you can either continue growing in the same soil, treating it as any other raised bed, or spread the compost elsewhere and construct a new Hügelkultur bed from scratch. In the meantime, the mound can always be topped up with more soil and mulch as needed.

A Bit of Background Information

First up: although I did search online for academic studies of Hügelkultur in an orchard setting, all I could find via Google Scholar was a December 2022 report entitled Hügelkultur : what is it, and should it be used in home gardens? which states that there were “no peer-reviewed, scientific studies on Hügelkultur”³Chalker-Scott. (2022). Hügelkultur : what is it, and should it be used in home gardens? Washington State University Extension. https://doi.org/10.7273/000004616 available at the time of publication. In this article, the author seems to dismiss the value of Hügelkultur growing as a bit of a fad. They do so mainly on the basis that it hasn’t been scientifically studied and peer reviewed – which is a science-first position that I can certainly sympathise with – but also because the original concept might have been influenced by the writings of “Austrian esoterocist”⁴Wikipedia entry on Steiner, accessed 13th April 2023. and biodynamic growing advocate Rudolf Steiner and I rather suspect the report’s author is not a Steiner-fan.

With that in mind, I’m going to go ahead and apply a bit of common sense horticultural knowledge and outline what I think are a few potential benefits that could apply to using a Hügelkultur system at a small orchard or allotment scale.

Secondly: a note that I’m far from the first or only orchardist to consider the uses of Hügelkultur in an orchard setting. A quick Google search turns up this article: ‘Modified Hügelkultur Mounds for Fruit Trees‘, which provides details of a permaculture-based method for longer-term fruit tree growing, complete with companion planting lists and details of a suitable irrigation system setup. If this is the sort of info you’re looking for, I suggest you switch blogs and go read that post instead.

Instead, I’ll be focusing on the potential for using a mature – from year two to years four, five or six – Hügelkultur bed in a limited timeframe: for the crucial first year of a newly-grafted tree’s growth and development.

Please note: none of the following is particularly scientific – I didn’t even have a one-year-old soil-grown or pot-grown tree to run comparisons with – and as far as I’m aware none of the discussion points or suggestions have been scientifically studied and/or peer reviewed either.

Also: I’m not saying Hügelkultur growing is necessarily better than existing, regular orchard nursery methods, just that I was very happy with the results I noted. I welcome your thoughts, observations, ideas and/or questions, via the comments.

The Potential Benefits of Hügelkultur in an Orchard Nursery

1. Burying and Composting, not Burning

I’ll start with a more general benefit to using the Hügelkultur method in an orchard. The construction of the mound involves the use of large and small pieces of woody material, such as the prunings and trimmings of top-fruit trees, hedging plants, or soft-fruit bushes, any or all of which are likely to be plentiful in an orchard, or even just on an allotment plot.

This sort of material could of course be used elsewhere: in log piles to provide natural habitat, as support or infill for dead hedging, or maybe as raw materials for carving and wood-turning. But if you’re not planning to engage in any of those activities, or simply have a surplus of pruned material to dispose of, then composting it in a Hügelkultur bed offers an attractive alternative to the other common method of disposal: burning; as fuel for log burners or food smokers, or to produce wood ash to add to the compost heap. Burning will obviously release large amounts of the wood-stored carbon into the atmosphere, whereas composting will see that carbon incorporated into the soil instead, or consumed by the billions of macro- and micro-organisms that live in the soil of the mound.

The resulting organic matter-rich soil is of course hugely valuable in its own right. It’s nutrient rich, but in a less concentrated form than fertilisers or manures, is usefully loose-textured, and of course provides an ideal habitat for the aforementioned host of beneficial soil organisms.

2. More Water Retention = Less Irrigation

On to some tree-specific benefits. Plants need water to live, but they also need the right amount of water, at the right time. Too little: they die. Too much: they probably die as well. The best sort of soil is therefore the type that retains enough water to sustain the plants that are growing in it; holds onto the water long enough for the plants to access it when they need to, and does so in a form that plants are able to take up via their roots. All without holding onto excess moisture that could cause anaerobic soil conditions to develop, or tender new feeder roots to rot and die.

Newly-grafted fruit trees grow relatively rapidly⁵Assuming the graft is successful, of course. Otherwise you might find that just the rootstock grows relatively rapidly instead., so they require a steady supply of accessible water. The loose-textured, organic matter-rich soil that the materials in a Hügelkultur bed breaks down into as it matures is ideal: moisture-retentive and free-draining.

Even after a hot, dry spell, whilst the outside of the bed might dry out, you’ll usually find that the inside of a Hügelkultur mound still retains plenty of moisture. All of which means you’ll need to irrigate it less than if you were growing trees in pots, or even in the ground, saving both time and stored or mains water.

3. Strong Root Development and Easy Lifting

Most fruit trees don’t do well if they sit in heavy, wet soils, especially over winter, and as mentioned, excess water can be particularly damaging to the delicate roots of young trees. The raised profile and loose-textured structure of a Hügelkultur bed offers great potential for improved drainage, which is particularly useful if the soil in your orchard or allotment is on the heavy clay side.

In addition, the new tree’s root system ought to develop particularly well in the loose, rich soil of a Hügelkultur bed, as the growing roots will meet little resistance and won’t have to try to force their way through thick, solid soil.

This is the root ball of one of the newly-grafted trees that I grew on in the Hügelkultur bed last year:

That looks like a pretty strong, healthy root system to me, with plenty of new feeder root development amidst all that lovely, loose, crumbly soil. I only had to gently loosen the soil of the Hügelkultur bed with a garden fork to be able to lift the tree. It’s in perfect shape for transplanting, hopefully with minimal damage to those delicate new roots.

4. Freely Available Mycorrhizal Fungi

We’re often told that, when planting trees and shrubs, we should inoculate the roots with a liberal dose of mycorrhizal fungi. These beneficial fungi form associations with plant roots. This connection facilitates the transfer of nutrients from the plant to the fungus, in the form of photosynthates (carbohydrates and other compounds), and from the fungus to the plant in the form of water, and soil-borne minerals that the fungus’s fine-filamented hyphae can access, but the plant’s relatively much thicker roots might not be able to reach.

The type of mycorrhizal fungi we’re told to use is usually powdered or granular in form, and nearly always sourced from a purchased packet. However, mycorrhizal fungus is naturally present in the soil, in vast mycorrhizal networks. Those networks can be damaged by digging and, according to the RHS advice page, “may be less effective on frequently cultivated soils that have been heavily fertilised and manured”. A Hügelkultur bed, once constructed, is neither regularly dug nor manured, which ought to allow mycorrhizal networks to develop and flourish within the bed, and remain relatively undisturbed.

This suggests to me that growing newly-grafted trees in a mature Hügelkultur bed could be a good way to inoculate their roots from a plentiful source of these beneficial mycorrhizal fungi, thereby saving the expense of buying in powders or granules.

Speaking of the commercially sold stuff, tropical ecologist and fungi expert Merlin Sheldrake, in his book Entangled Life, discusses the idea that introducing packet mycorrhizal fungi to a growing area could actually be detrimental to soil health. He says: “…introducing opportunistic fungal species to new environments might displace local fungal strains with unknown ecological consequences.”⁶Merlin Sheldrake, Entangled Life (2020), p.163 Or, in other words, the packet mycorrhizal fungi might out-compete the native mycorrhizal fungi and become, in effect, a dominant monoculture which could potentially disrupt the existing network of microorganisms within the soil.

If that is indeed the case, then it seems likely that there will be a much lower risk of this happening if the mycorrhizal fungi have been growing in a Hügelkultur bed that was constructed with soil brought from elsewhere on the same plot; the local strains of mycorrhizae should be transferred to the bed along with the soil and then they will then be transferred to the planting location along with the transplanted trees as well.

Conclusions

To summarise: I think setting up a Hügelkultur mound to use as a nursery bed for young fruit trees once the bed has matured could be a rather good idea, for the following reasons:

1. Over time, the Hügelkultur bed composts and breaks down into nutrient-rich, loose-textured soil that’s an ideal medium for hungry, fast-growing young fruit trees.
2. The organic matter-rich soil of a mature Hügelkultur bed offers improved water retention, which both helps young trees grow well and reduces the requirement for irrigation.
3. Young tree roots develop really well in the loose-textured soil of a Hügelkultur bed, and the one-year-old grafted trees can be easily lifted for transplantation, with minimal root damage.
4. As long as you use soil from elsewhere on the same plot to construct the Hügelkultur bed, the native mycorrhizal fungi will be transferred as well, and will be able to grow and develop relatively undisturbed for the lifetime of the bed, also helping with the development of the young trees’ roots.

If you’ve successfully grown newly-grafted fruit trees in a Hügelkultur system, or have used Hügelkultur as part of a larger, permaculture orchard or forest food-garden, or if Hügelkultur is something you’ve not had much success with for whatever reason, please do let me know about your experiences, via the comments.

A Side-Note on Coincidental Companion Planting

The permaculture article that I linked to provided a long list of potential companion plants – dubbed a ‘tree guild’ – suitable for a Hügelkultur orchard plot, along with the benefits said to accrue from the inclusion of each plant. I don’t have any comment to make on that system as I haven’t tried the approach myself. But I did stumble upon a side-benefit from a different and very simple coincidental companion plant that I grew in the same Hügelkultur bed last year.

Noticing that there was plenty of room for more plants at the edges of the Hügelkultur bed, I decided to plant out a couple of dozen seedling Dahlias, in rows on either side of the newly-grafted trees. The Dahlias grew rather well in the rich, well-drained soil of the Hügelkultur bed, reaching about two to three feet (60 – 90cm or so) in height, and they bushed up nicely as well.

The effect on the newly-grafted apple trees seemed to have been to encourage them to send their leading shoot straight upwards, in order to stay ahead of the Dahlias in their search for light. The end result was a row of young trees⁷Not a whole row, as only 14 of the 20 trees I grafted last year successfully took and grew on. I suspect it had a lot to do with some overly-thick rootstock material, sourced from a supplier that I haven’t bought from again this year. that – no doubt also fuelled by the rich, free-draining Hügelkultur soil – seemed to have grown at least one stem that was usefully tall and straight. This meant they were perfect for growing on as single-stem cordons; the intended form for the trees in question.

Please note once more: I didn’t run any sort of comparison, either with newly-grafted trees that were grown in regular soil, or with new trees on more vigorous rootstock, with or without Dahlia companions; both of which could still have resulted in the same overall effect. I have in the past grown my newly-grafted trees in air-pots, and from what I can remember, their growth patterns have tended to be less vigorously upright and involved the development of more branching side-shoots.⁸But perhaps that has more to do with irregular irrigation than the actual method of growing.

Whilst I’m not claiming that Dahlias are an absolutely perfect companion plant for newly-grafted apple trees, on this occasion the outcome seemed to be a favourable one. I’ll hopefully be using the same method again this year⁹If the Dahlia seeds I sowed last week ever get around to germinating…, so whether the results are similar or markedly different, I’ll be able to report back next spring.

Footnotes

• 1
  Over on my old allotmentnotes.com blog I posted an article on building a Hugelkultur bed (the very same one that we’re talking about here, as it happens), if you’d like to read a bit more about the process I followed.
• 2
  Not an autumn build, I know, but I’d only just learned about the method, had a lot of woody prunings to get rid of, and didn’t want to wait all year to get started.
• 3
  Chalker-Scott. (2022). Hügelkultur : what is it, and should it be used in home gardens? Washington State University Extension. https://doi.org/10.7273/000004616
• 4
  Wikipedia entry on Steiner, accessed 13th April 2023.
• 5
  Assuming the graft is successful, of course. Otherwise you might find that just the rootstock grows relatively rapidly instead.
• 6
  Merlin Sheldrake, Entangled Life (2020), p.163
• 7
  Not a whole row, as only 14 of the 20 trees I grafted last year successfully took and grew on. I suspect it had a lot to do with some overly-thick rootstock material, sourced from a supplier that I haven’t bought from again this year.
• 8
  But perhaps that has more to do with irregular irrigation than the actual method of growing.
• 9
  If the Dahlia seeds I sowed last week ever get around to germinating…