Pallet wood Hydro-driver theory, construction guide

In a nutshell…

The Pallet wood Hydro-driver is a ‘mechanical’ way of actively driving moisture out of water-saturated ‘heavy-clay‘ soils during the critical root development stage of March, April & early May. Its is especially suited to overly-bred modern ‘woody annual vegetables‘ that require a high flow of water over their roots but do not like it soggy. Its does this through a physics principle called the ‘Stack Effect‘.

But this isn’t all its doing…


Lastest design for 2018

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Things to consider with this latest improved design..

  • Uses Recycled plastic lumber struts
  • Slats are attached using TurboCoach screws for easy replacement
  • Open stone-retaining base from 1/2 inch Aviary galvanised-metal mesh
  • Drilled holes in elongated plastic struts to allow a metal stake to be slotted across the top to act as a swivel / attachment point
  • Lighter more manageable design
  • A half buckets worth of large conker sized flints or stones are poured into each half of the stack once its in situ

Thanks to EcoPlastic of Leicester for supplying the recycled plastic struts / stakes and expertise.

Eco Plastic Ltd of Leicester

Science behind the Pallet wood Hydro-driver.

The Pallet wood Hydro-drivers main task is as a ‘soil moisture level‘ moderator. It achieves this using mainly a physics principle called the ‘Stack Effect‘. But also the large conker sized flints or stones within the Hydro-driver void suck in the cold early dawn temps which then as the sun rises moisture condenses onto these cold stones via the large air gaps in the stones. As the ambient air temperature begins to rise (Sun rises) and air flows across the narrow opening of our Hydro-driver. An uplift of moisture heavy air is created and is wicked away.

The absorbing but drying-on-one-side quality of the lower wooden slat in the design also creates a -negative moisture zone (dryer) at the centre of the growing bed which gradually exerts a ‘hydrostatic pull‘ across a large section of the paired planting bed sucking water from the +positive moisture zone of the Wood chip sock borders horizontally across the growing bed leading to moderated, non-saturated and consistent moisture levels within the growing bed. This hydrostatic pull also seems to be liberating nutrients and minerals from the soil more rapidly. In comparison to boxed-in “raised beds” with their easily over filled soil levels working against your plots natural water table. Stopping the natural wicking effect and therefore slowing transpiration and stalling growth. Also in the traditional open-soil approach water is wicked away from a large surface area across your whole plot. I believe my Pallet wood Hydro-driver design helps sustain a ‘Goldilocks level‘  of  optimal soil moisture levels leading to steady transpiration and sustained growth.

Also another useful part of the design is that because the soil is stacked against the hydro-driver it supports and slows compaction of the soil from gravity and weathering over the growing season. The Pallet wood Hydro-driver also acts a platform for treading on or hooking on attachments such as my g.easel (Gardeners Easel) 4-in-1 design; Squash Trellis, Bean frame, Windbreak and Cloche (G. Hamilton).

NOTE: Orientation along a North-to-South axis is crucial to this design. If the pallet wood trough is sunken into the soil along a East-to-West axis basically face-on to the sun it will completely dry out your growing bed due to the drying efficiency of the Hydro-driver design. During the warmer months of June & July it may be necessary to loosely place a plank  across the top of the Hydro-driver void to halt its evaporating function. Also by this point in the growing season your plants roots balls should be established and effectively they are now the Hydro-driver.

The nylon handles at either end of the design make it easier to remove at the end of the growing season (Sept/Oct) for storing under a tarp for storing over the winter.

NOTE: This Hydro-driver is not required for your traditional English veg such as Potatoes or Root vegetables which tend to like cold and wet heavy soils. Where I have had success is with outdoor tomatoes, chillies, courgettes, aubergine and onions. I have nine bed system on my plot and only use x6 Pallet wood Hydro-drivers on three of the beds (x2 to each bed).

A final note on this design with regards the lower slat that is sunken into the soil. Because this slat is acting like a straw it rots down in 1 to 2 seasons however I think this is a positive as the white mycorrhizal fungi that is visible across the rotting slat when pulled up at the end of the season has an additional benefit. I believe that not only does this funghi supply the roots of woody annuals with essential nutrients through a symbiotic relationship but that the anti-microbial action appears to be limiting the spread of ‘blight‘ within this planting bed. I have had no blight in these beds over 4 growing seasons but have had blight on other non Pallet wood Hydro-driver separated beds.

Evolution of the Pallet wood Hydro-driver design

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Pallet divider mk2

Pallet wood hydro-driver design mk2 from 2017

After the initial observation of witnessing robust growth using a central pallet wood stack during 2015 in my heavy Essex clay soil I made the mistake of not fully understanding what was going on with the design. During the last couple of years by creating an impermeable closed base (plastic[2016] then metal [2017])  to the design which I now understand actually hindered the stacks moisture moderating function. It has taken me 4 growing seasons to fully understand and perfect the design.

Dismantling a Standard 2-way entry pallet

There are a few different types of pallet designs and we require a specific type that is generally used to transport bricks. It is called a Standard 2-way entry pallet. It is different from the majority of pallets in that it has 4 or 3 strong vertical struts that the pallet slats are nailed to. You will also notice the basic tools required to build our Pallet wood Hydro-driver; Wood saw and claw hammer. I am also using a newly designed tool called a ‘Roughneck Demolition and Lifting bar’ from Toolstation, that makes levering up the slats easier without damaging them too much.

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Using the Roughneck bar to prise up the slats away from the vertical struts. Always ease up the slat from the central strut to start as it loosens the slat before fully prising up the sides then moving back to the central strut to finish prising the slat off.

For the nails left behind in the struts, give them a couple of taps. It will drive them in a little bit. This make it easier when pulling them out with a claw hammer / crowbar. Breaks the rust / wood meld.

The pallet very nearly dismantled

Fully dismantled pallet


Constructing your own Pallet wood Hydro-driver

12.03.2018 Construction guide of the latest mk3 2018 design pictured above to follow once the weather improves. Photos always look best on a nice sunny day !