PhysicalWeeding: The 4 Wheel Hoe -The Ultimate Pedestrian Hoe

The 4 Wheel Hoe - Free under an Open Hardware License

As of October 2022 the 4 Wheel Hoe has been released under an Open Hardware License so that anyone can now download the plans for free and build their own machine. The Open Hardware License also allows people to build and sell 4 Wheel Hoes and modify the design according to the License. All the 4 Wheel Hoe documents, the rational, the plans, the blade length and users guide have all be combined into one document. Download it from the Physical Weed Control Forum

Download the full documentation for The 4 Wheel Hoe from the Physical Weed Control Forum

Happy weeding!

Image Galleries of the 4 Wheel Hoe

Video of the 4 Wheel Hoe on Vimeo - video 1, video 2

Summary

Introduction

The 4 Wheel Hoe addresses a crucial gap among weeding machines. While there is a burgeoning choice of tractor-mounted weeding machinery for larger scale growers, smaller scale growers and farmers only have a choice between modern one-wheel, or antique two-wheel, wheel-hoes. While brand-new one-wheel hoes are flexible this comes at the sacrifice of usability and effectiveness. In comparison, two-wheel hoes are a considerably superior design, however, the lack of current manufacturers means they can be difficult to locate and often considerable ‘TLC’ is required in their use and upkeep. The 4 Wheel Hoe is a revolutionary new concept that solves this problem. It has been designed from first-principles of physical weed control, engineering efficiency, and usability to fulfill the in-crop weeding needs of commercial growers producing crops grown on the bed system, i.e., not on ridges, with fields to large to practically weed with hand hoes, yet too small to justify the expense of tractor mounted weeding machinery. The result is a machine that looks very simple, even basic, but is the result of hundreds of hours of deep deliberation and brain-bending analysis coupled with extensive field testing to ensure every single component is optimised for its purpose. The result is a hoe that is supremely effective while easy to use and very robust, or to put it slightly more poetically, the 4 Wheel Hoe is designed to last long enough to pass down to your grandchildren and so effective they will be grateful to have inherited it! 

Wheel hoe toolframes. PhysicalWeeding's 4 Wheel Hoe (top), typical one wheel hoe (bottom left), typical two wheel hoe (bottom right).

The 4 Wheel Hoe Design Concept

The essential design aspects, both biological and mechanical, of hoes were established over a century ago, and are exemplified by the ‘Nicholson Webb’ L bade hoe. However, after 50 years of nearly complete dominance of weed management by herbicides, most of this knowledge has been lost from living memory. This has resulted in well intentioned, but unfortunately, considerably sub-optimal hoe designs, especially in the area of pedestrian hoes. The 4 Wheel Hoe has been designed to squarely address this problem. It has been designed from scratch, working from the primary principles of how knife-blade hoes kill weeds, combined with the best engineering and ergonomics to produce a machine perfectly matched to its job. The design of the 4 Wheel Hoe literally starts at the ‘cutting edge’ where steel meets soil and weeds…

Nicholson Webb L blade hoe

Horizontal knife-blade hoes

Horizontal knife-blade hoes kill weeds through a combination of severing, burying and uprooting. To effectively kill weeds by severing they should be cut through the hypocotyl stem - i.e., the stem below the cotyledons and above the roots. The hypocotyl stem often starts only a few millimetres under the soil surface so hoeing too deep merely undercuts and transplants weeds. Keeping the hoe blade as close as possible to, but still ensuring it remains under, the soil surface, results in the greatest possible weed kill and also least soil resistance (draft). However, this requires very precise depth control.

Mini-ridgers - killing weeds by burial

Small weeds, typically two true leaves or less, can be killed by burial under just two to three centimetres / an inch of soil. This is because the hypocotyl looses most of its ability to expand once the cotyledons have unfurled so it can’t push through the covering of soil. Burial therefore deprives the seedling of light at a time when it has exhausted the nutrient and energy reserves in the seed but has not yet produced much, if any, of its own. It therefore has little or no ability to produce new shoots to grow up through the new layer of soil. This effect can be used to kill intrarow (within the crop row) weeds without harming the crop, even ‘next to crop’ weeds - the ‘holy grail’ of physical weed control. However, for this technique to be practically effective sufficient soil has to cover the weeds to kill them without covering the crop so much that it is killed or significantly harmed. For crops at early stages of growth the difference in soil depth that achieves effective weed kill without crop damage can be only a centimetre or two. Consistent and accurate burial depth is therefore essential to maximise weed kill while minimising crop damage. Therefore, just as for knife blades, mini-ridger also depend on very precise depth control.

   
4 Wheel Hoe: T hoes and sight guide (left), mini-ridgers (right).

Four wheels give optimum depth control

One and two wheel hoes are clearly unable to provide the very precise depth control required for the twin tasks of keeping horizontal knife blade and mini-ridger hoes at their optimum depths, as they rely on the user to control the depth via the hoes handles. Worse, in the case of one wheel hoes, lateral stability also has to be maintained by the operator, the result is highly variable depth control - the opposite of what is required. Mounting tools between four wheels gives the most stable, precise and practical depth control practically possible, i.e., in engineering terms it is an optimal design that cannot be surpassed. The same principle underlies mid-mounted toolcarrier tractors, road graders and many seed drills. Therefore, the optimum design for a wheel hoe is four wheels, no more, no less. Hence the 4 Wheel Hoe was born. While four wheels gives the best possible depth control, building a hoe based on this principle while also achieving all the other design requirements, such as effectiveness, usability, ergonomics, practicality, simplicity, low weight without an exorbitant price was no simple task. Many of these objectives conflict with each other, requiring innovative solutions to solve these dilemmas. Here are just a few examples…

Fiat tool carrier tractor with mid-mounted roller-undercutter and rear mounted Stanhey Mk II belt seeder with the drill units situated between two rollers (wheels)

Optimum knife hoe blade design

To kill weeds by burying and/or uprooting them requires that the soil they are growing in be mixed and broken up by the hoe blades as much as possible. However, mixing requires energy (increases draft), so a balance must be struck between soil churn and energy used. Also plant resides are often tough and have the potential to cling to and block soil engaging parts such as hoe blades, especially those with low sweep angles. The optimum solution for these issues is a knife blade with 15° rake and 60° sweep angles, as used on the 4 Wheel Hoe’s, T hoes.

In contrast the ‘stirrup’ / oscillating / ‘Swiss’ hoes, popular on modern one wheel hoes, fail practically all hoe blade design requirements. For example, with stirrup and other low sweep angle hoe blades the hoe needs to be endlessly pushed and pulled backwards and forwards to clear weeds and plant residues from the blade. No farmer would accept a tractor mounted hoe that has to be constantly edged forwards and backwards to clear it of weeds and plant residues. Imagine how little work could be achieved with a tractor mounted hoe that required such an action? So why put up with such an approach in a pedestrian hoe? The 60° sweep angle of the 4 Wheel Hoe blades ensures effective self cleaning so it can be just pushed forwards so there is no need for the endless pushing and pulling required with stirrup hoes. With the stirrup hoe the rake angle changes as the blade oscillates and as the user moves the handles, plus the concave shape means that the blade depth varies across the hoe’s width, all of which reduce the hoe’s effectiveness. The 4 Wheel Hoe has its blades set at the optimum rake and sweep angles which are maintained by the hoe not the user resulting in maximum effectiveness.

Rather than using the more traditional L blade hoe (as per the Nicholson Webb, and one and two wheel hoes, above) T hoes (so-called because they are shaped like an inverted capital letter ‘T’) have the leg positioned well clear of the crop so the blade can slide underneath crop foliage. This means the horizontal blade position only has to be altered when the plants’ stems grow larger, rather than the foliage. In comparison an L blade hoe has to be moved away from the crop as the foliage grows to avoid damaging it. This means that a T hoe can hoe more of the soil surface at larger crop sizes than an equivalent L hoe so killing more weeds for longer into the crops life. It also means that one width setting for the blades can accommodate a wide range of crop sizes, and only small width adjustments will accommodate all crops thereby minimising the need to adjust the hoe between different crops - essential for the small scale producer with a wide range of crops.

How mini-ridgers work

The blade height of mini-ridger blades determines the maximum size of the ridge they can create, even if they are placed too deeply in the soil, as excess soil simply flows over them. By correctly matching blade height to the crop size it is almost impossible to bury the crop as long as a suitable tilth and soil conditions (e.g., not too wet) are present.

Therefore, with both the T hoes and mini-ridgers working together on the 4 Wheel Hoe, 100% control of small weeds in one pass, both in the interrow and intrarow, is now possible. This represents as big an advance, if not more, in manual weed control as the invention of the wheel hoe itself.

However, optimum blade design is only part of the 4 Wheel Hoe concept…

Easily accommodate different intrarow and interrow widths

Crops fill the row space as they grow and they can be sown in single, double and triple bands. This all means that the distance between the tips of the hoe blades (the crop gap) has to be altered to fit the crop’s size and the number of seed bands. The 4 Wheel Hoe achieves this using a bottlescrew / turnbuckle system which moves the two sides of the hoe closer or further apart rather than adjusting the hoe blades and other implements individually. This means that the width of the blades can be adjusted completely independently of the depth, so eliminating the highly frustrating situation found on other hoes (especially tractor mounted hoes) where the width and depth of a blade are adjusted at the same time - often resulting in one position being lost while the other is changed. Central width adjustment also means that all tools are adjusted at the same time, which is a particular boon where many tools are attached to the toolbars in precise positions as changing them individually would be very time consuming. In addition the mini-ridgers can also be adjusted independently so ensuring that the optimum size soil ridge can always be formed regardless of the T hoe crop gap.

Another significant advantage of the T hoe, is that it needs to be adjusted both less frequently and by smaller amounts that an L blade hoe. This is because the L hoe leg is positioned right next to the crop, so as the crop grows or the hoe is moved between different sized crops, the leg position has to be continually adjusted. In comparison the T hoe has the leg in the center of the blade and therefore close to the center of the interrow area, i.e., as far from the crop as it is possible to get. As the leg is far from the crop the T hoe only needs to be adjusted if the ends of the blades would hit the crops roots - a far smaller target than spreading foliage. This means the 4 Wheel Hoe needs much less adjusting compared with an L blade hoe when changing among different types and ages of crops.

With the centralised width adjustment system the 4 Wheel Hoe can be set up to fit down a wide range of interrow widths from as little as 15 cm / 6” upwards, although 20 cm / 8" is considered a more practical minimum width, with 25 to 30 cm / 10" to 12" considered optimum.

Ergonomics

Any physical job that has to be undertaken regularly, especially for hours at a time, can be made much easier by good ergonomic design. The 4 Wheel Hoe has incorporated the best ergonomics from the start of the design process. Removing the need for the operator to control hoe blade depth and no longer push and pull the hoe, as described above, are very substantial ergonomic improvements in and of themselves. In addition the hoe travels over the crop row, rather than beside it so the operator walks squarely behind the machine so they don't have to twist their body to sight the hoe up with the crop. The long handles give a clear view of the tool which allows for upright posture and the sight guide takes the guesswork out of accurately pacing the hoe. Most of the handle’s weight is supported by the hoe so removing the need to continually lift the handles (the hoe will stand upright without any assistance). The ability to change (both vertically and horizontally) where the handles attach to the hoe along with the handles quick and simple height adjustment (via the handle clamp) means that an optimum weight transfer can be achieved for a wide range of soil conditions, so that the force of the user pushing the hoe is balanced by the weight of the machine, thereby ensuring as much of the users effort goes into pushing the hoe blades through the soil and nothing else.

The handle grips have the optimum diameter for the average human hand grip and for any ‘Incredible Hulks’ the size can be increased by slipping a piece of water pipe or wheel barrow hand grips over the handle ends. The hand grips are also in the correct vertical orientation for human hands, i.e., if you leave your arms loose at your side and then bring them up to the handles no rotation of the wrist / forearm is required. The variable height system also means that the wrists are kept straight, rather than bent, when pushing the hoe. The handles are the same width as an average persons shoulders, so keeping the arms in a neutral alignment. This all aims to minimise fatigue in hands, wrists, arms, shoulders and back.

The long arms also allow a more natural ‘pushing position’. Whether the upper arms are by the users sides and lower arms pointing forwards at 45° or if the user prefers to lock their arms out straight, the handles can be positioned so the user can maintain a healthy upright posture, rather than being bent over to put their ‘weight’ into propelling the hoe. This all adds up to reduced fatigue, lower risk of injury, especially chronic strains, and therefore happy healthier staff as well as higher work rates.

For those that prefer to have a horizontal hand grip, there is the opportunity to hold the hoe using the cross bar. This is also handy when moving the hoe between jobs as pushing down on the cross bar lifts the hoe onto its rear wheels thus keeping the blades clear of the ground for easy transport and manoeuvring.

Usability

There can be few things as frustrating and annoying as spending a load of time heading out to the field to do a job, only to find that an adjustment is required or something needs fixing and the tools you need are back in the shed. The 4 Wheel Hoe, only requires a single 19 mm / ½” spanner / wrench to make any adjustment or change. Such a tool is easily carried in a pocket, or hung from the hoe.

Flexibility

The standard toolbars, clamps and tool-legs allow a very wide range of weeding and other tools to be attached to the weeder, including user-designed equipment, making it exceptionally flexible. This makes the 4 Wheel Hoe more like its tractor mounted brethren than other wheel hoes with their proprietary tool attachment systems. Additional clamps and tool legs are available at fair prices so if you want to develop your own tool or attach a favourite pieces of equipment to your 4 Wheel Hoe, then no impediments in the form of expensive proprietary componentry stand in the way.

The wheels also have multiple attachment points and tools can be clamped anywhere along the toolbars (except where the wheels are of course!)

The highest build quality

The 4 Wheel Hoe is designed and built for exceptional strength and durability. This is exemplified by the use of stainless and galvanised steel, plus robust wheels with non-pneumatic, puncture proof tyres. It is a professional machine designed and built for decades of use by professional growers.

False seedbeds

The 4 wheel hoe is also an excellent tool for tilling (cultivating) false seedbeds (i.e., where a planting tilth is created, then left for weeds to germinated, which are then killed by minimal tillage). To minimise the amount of passes required it is recommended that a second set of full length T hoe blades are purchased for this job so as wide an area of soil can be tilled in one pass as possible.

The Caveats

Few designers or manufacturers tell customers of their machines limitations up-front, but PhysicalWeeding prides itself on its honest relations with clients. We are farmers and growers ourselves so understand the importance of not overselling equipment. Having said that we also pride ourselves on designing and building the best machines conceivable so our caveats are few and far between and in most cases they are not unique to our machines but apply equally to machines sharing the same principles, e.g., all horizontal knife blade hoes.

Weeding crops grown on the flat vs. ridges

The 4 Wheel Hoe is not designed, and is unsuitable, for use on ridge cropping systems, e.g., potato ridges. It is only for use where crops are grown on flat ground, typically the vegetable bed system (either raised or flat beds) or any system where the soil surface immediately surrounding the crop is flat. While the 4 Wheel Hoe can travel over or between ridges, and it may appear that the weeding requirements of both ridges and flat ground are similar, they are in fact dramatically different. For example, a flat bed (if it has been properly tilled / cultivated) is effectively a smooth two dimensional surface, while a ridge (regardless of how careful soil preparation was) is a very variable three dimensional surface. It is therefore considerably more difficult to precisely follow the entire soil surface of a ridge compared to flat soil, so therefore, ridges are much harder to precisely weed than flat soil. There are also many other problems manually weeding ridges, such as needing to walk in the furrow while having the weeder run on top of the ridge resulting in off-center draft forces and skewed line of sight. Beds and ridges therefore require quite different approaches and tools to effective ally weed them. For example, tractor mounted weeding tools (not tool frames) designed for one system are rarely capable of weeding the other, e.g., a horizontal axis brush hoe can not be used on ridges and a potato ridger would destroy crops grown on a bed. The same goes for pedestrian weeders: either you have a tool that is optimally designed for one system that achieves the best possible results; or you have a jack-of-all-trades machine that accomplishes average results in both systems. The 4 Wheel Hoe is an example of the former, one wheel hoes an example of the latter.

At the same time, ridge crop systems are only an optimal production approach for a small number of crops. Tubers, such as potatoes, have to be grown on a ridge to facilitate harvesting, and a few root crops, e.g., parsnips, especially when grown to large sizes for processing, are best grown on ridges, again, to facilitate harvesting. The other key reason for using ridges is that when soil conditions are wet and/or cold, ridges can help warm and/or drain the soil, thereby increasing crop performance. Some other crops, e.g., the larger brassicas such as broccoli and cauliflower are equally suited to both ridges or beds in terms of best use of field space, as their large space requirements (low plant populations) can fully utilise the larger interrow spaces (distance between crop rows) associated with ridges. However, this is often at the cost of accurate weeding compared with bed production, so these crops are better grown on beds when possible. Almost all other crops are best grown on beds, as this facilitates much greater accuracy of inter- and intra-row weeding, as machines only have a two, rather than three, dimensional surface to weed. Beds also make better use of field surface area, i.e., more plants can be grown on the same area of land than on ridges, due to the smaller interrow spacing possible on beds. Having smaller interrow spacings, and therefore higher field populations, also increases the area of soil covered by crop foliage thereby increasing crop competition with weeds, further adding to the advantages of the bed system. In short PhysicalWeeding strongly recommends the adoption of the bed system rather than ridge cropping for the vast majority of crops as it is a superior production system.

Suitability for different soil types and stones

The 4 Wheel Hoe is not suitable for all soil types: Stones larger than about 5 cm / 2” across can significantly hamper the effectiveness of the hoe, as they will any precision horizontal knife blade hoe. Soils with significant amounts of large stones will be difficult to impossible to hoe. Similarly, the soil tilth needs to be fine and level. Lumpy, uneven cloddy soils and those with high levels of plant residues, will prevent the hoe working effectively.

Soils that set hard will also be a serious impediment to effective weeding as the effort required to push a hoe through such soils is more than most humans can manage. This equally applies to trying to weed tractor wheelings - they are too hard and compacted to be weeded by a hoe designed for precision weeding of vegetables. You will be better off getting a cheap old toolbar to go on the back of a tractor, with a set of spring tines with duck’s feet sweeps to clear wheelings of weeds, because accuracy is not an issue, but speed, brute force and aggressive soil penetration are the ‘name of the game’.

Effect of soil moisture and weather on weeding effectiveness

Horizontal knife blade hoes won't work nearly as well in wet soils or wet weather as the soil does not flow as well, and weeds have a better chance of re-establishing themselves post-hoeing. This equally applies to the T hoes on the 4 Wheel Hoe. However, as long as the soil is not so wet that forming a good mini-ridge that effectively buries weed seedlings is still possible, then weed kill with the ridgers will still be good, because this means of killing weeds is only marginally affected by soil moisture or weather conditions as the weeds are killed by light deprivation not desiccation.

Width adjustment and row spacing limits

There is a trade-off between adjusting the 4 Wheel Hoe for different intrarow and interrow spacings. While the 4 Wheel Hoe can accommodate row widths (interrow) as small as 15 cm / 6” and it can be quickly adjusted to deal with different crop gap sizes (intrarow) the fixed length of the T hoe blades means that it cannot be so quickly swapped between widely differing intrarow and interrow sizes at the same time. This limitation applies to all horizontal hoe blade designs. The solution requires the use of different length T hoes and potentially mini-ridgers. While this may appear an undue restriction for growers used to hand-hoeing, it is an inevitable constraint faced by growers using tractor mounted hoes. For growers using tractor mounted hoes it is often simpler and more economic to have just one row spacing for every crop, such is the time and hassle involved in altering hoe settings. It is therefore recommended that as small as possible range of interrow spacings are adopted for use with the 4 Wheel Hoe, with ideally just one spacing used. However, if widely varying interrow widths are essential then swapping different length hoe blades and changing the 4 Wheel Hoe width only takes a handful of minutes, much less than for tractor mounted machines.

While the 4 Wheel Hoe can get down 15 cm / 6” rows, it’s a tight squeeze, and the outside of the wheels are right next to the adjacent crop rows. Therefore, there is no margin of error, e.g., for the interrow distance to vary or room for crops to grow sideways. Interrow spacings of at least 20 cm / 8” for very upright crops and 25 cm / 10” for most crops are recommended. While it is possible to reduce the width of the 4 Wheel Hoe (by having smaller bottlescrews) so it could effectively fit down 15 cm / 6” rows there would be such a loss of lateral stability (greater side to side wobble) that its effectiveness will be hampered. However, if it is essential to grow crops in such narrow rows, the hoe width could be set so it straddles two crops rows rather than one. This will however, require a custom hoe blades and attachment system, please contact Merf if you would like to discuss this idea.

While there is no mechanical upper limit on the row spacings the Four Wheel Hoe can be used on, there are practical limits to the effective width of a horizontal knife blade hoe. This is due to variation in soil height (undulations) which mean that the longer the blade, and/or the further the blade is from the depth wheel, the greater the likelihood that some parts of the blade will be too deep and others too shallow. This will depend on soil conditions, especially how level tillage implements leave the soil, so it will therefore vary between farms. A maximum blade length of 60 cm is suggested as an upper practical limit on beds that are exceptionally flat and uniform. For rougher tilths, shorter lengths will be required.  

Return to top