One of the most common questions we’re asked here at Ergrownomics is: “and you’re sure those are deep enough to grow [such and such]?” It’s a fair question, not least because of the amount of misinformation out there! When buying a planter or building a raised bed at home – the last thing you want to do is not make it deep enough, and stunt crop growth – particularly if you’re concerned that you’ll mostly be growing longer-rooting crops.
With this in mind, we’ve set out this blog to try and explain a little about crop rooting depth, and dispel a few entrenched myths around the subject. Roots are essential for anchoring the plant, as well as providing it with the relevant nutrients and water it requires to grow. The length at which these roots might extend down varies from crop to crop. However, it wouldn’t be unfair to assume that certain crops may need more space below the soil surface than a lot of raised planters appear able to provide!
The majority of responses to this limited container depth (and soil thickness) have been to err on the side of caution, and gardeners are advised to be careful when deciding which crops to select. In some cases, would-be growers abandon the idea of producing certain vegetables altogether. The suggestion put out by most bloggers has been to marry the variable lengths of roots to the amount of space permitted by the depth of their planter, and consequently, people turn to specially constructed soil depth charts. These charts (as featured) display three distinct categories of rooting depth for different crops: shallow, medium and deep rooting. Attached to each category are different depths: 12”-18” for shallow, 18”-24” for medium and 24”-36” + for deep roots. Additionally, the measurements for required root depth are specifically for a mature crop.
The trouble is, this rigid categorisation of root depths would suggest a host of limitations regarding raised planter gardening more generally, and insist that the depth listed is a requirement for the crop, as opposed to a given preference for a certain variety!
Tables like this one are rampantly shared throughout the gardener community, and while meant as a helpful guide, actually lead to myths that are – at best - very limiting. We fear that the inferred limitations of growing in a finite space may turn people off of container gardening altogether!
Luckily, and through careful and thorough experimentation by the Ergrownomics team, these myths have been studied and debunked. The potential pitfalls regarding soil depth and raised planters are outlined below, as we look to dismiss these claims and allow you to get the best out of your garden, with whatever space is available.
Myth 1: You can’t grow deep rooting vegetables in compact raised planters
The chart above would suggest that deeper rooting veg are a no-go for people with a raised planter - however - this is wholly reductive. Perhaps most importantly, these tables fail to consider inter-species variation, and account for the habits of different varieties.
Take the example of the carrot. There are nearly 50 different families of carrot, each with their own characteristics.
Choosing the most suitable variety then, plays a vital role in the success experienced from container growing. Varieties are available for all crops, but be careful not to immediately gravitate towards stumpier variations on the basis that they will require a shallower depth of soil! To help Ergrownomics owners, when you buy a planter we give you private access to our own Crop Selector application, letting you know which varieties we’ve tested respond best to compact, container growing – as well as how many to plant per row, and when to sow!
Let’s take our earlier carrot example. Two families of carrot are the ‘Imperator’ carrot and the ‘Chantenay’ carrot; the former (Imperator carrot) tends to grow longer and thicker, while the latter (Chantenay carrot) is comparatively shorter and stumpier. It would be forgivable to assume then, that the stumpier, Chantenay carrot would be a preferable option to grow in containers: it is shorter and so would not require as deep a soil profile, right?
Wrong! We’ve found time and time again that length of crop or root depth are not the key limitations of container growing. Imperator carrots grow long, straight roots, and are less competitive – and while they choose to grow to the maximum depth of our planter, they rarely intrude laterally into one another’s space! The Chantenay carrot, however, doesn’t react well to close spacing – and so tends to grow into a mangle of small, woody and sprouting roots!
In fact, when growing almost anything, on top of considering root depth in tandem with the height of the plant, you also need to consider crop habits. Does the crop mind to growing near to others (close spaced crops)? Do they grow well in rows (line growing)? These are just a few of the questions that raised planter gardeners should start asking themselves, and questions we’ve answered in our Owner’s Area.
Root depth is only a small piece of the overall puzzle!
Myth 2: You should grow and plan for crops at full maturity
As is the case in these tables, the root depth measurements correspond to the mature plant. This means that, chiefly, it is the maximum root depth and overall size above the soil that are considered. The idea is that maximum yield comes with a mature plant that has had more time to grow.
However, whilst true that mature plants are invariably larger, we don’t believe that this is necessarily the most desirable thing!
Take Chard as an example. Chard leaves, when grown to maturity, become far less succulent than their younger selves, tasting more woody, waxy, and generally less tasty! We prefer to grow chard for its baby leaves, and switch it out of our planters for something else when it begins to age! When picked regularly, chard will invest more energy and sugars into replacing its tasty leaves, and invest less in its roots. If left unchecked, the leaves grow too large, and not only taste less appealing – but begin to physically battle for above-ground space! In summary then, preventing the crop from reaching maturity means a better taste, more control over its size, and subsequently, a more efficient ratio of container space to crop numbers.
Myth 3: Deeper beds are better because they don’t dry out as easily
This is one of the stronger arguments for a deeper soil profile. Water in deeper soils are (naturally) held at a greater depth, and so protect the bed from rapid drying that takes place nearer to the surface. Less volume typically leads to an increased risk of desiccation, and dehydrated plants!
However, the disadvantage of comparably shallow, raised containers can be offset by an efficient and optimised irrigation system. Our tailor-built, drip irrigation system is modelled on the natural water cycle. Pressure compensating emitters equally spaced across our drip-lines maintain a constant flow. The moisture leaves the tubing and infiltrates the soil at the surface, concentrically around the drip-line to form a uniform wetting pattern. In layman’s terms, this means that an optimum soil moisture content is maintained, hydrating the soil regularly and reliably. Our soil scientists have found this approach to be 60% more efficient than using a watering can!
Notably, our method is in direct opposition to the approaches adopted by a lot of competitor brands. Capillary irrigation systems, while popular, are actually quite harmful to crops. Reservoirs of water sit at the base of the beds, fighting a losing battle against gravity, and so the water supply is inaccessible to the seedlings above. In the event that any roots were able to reach the water supply, they would become overwhelmed and water-logged, which quickly leads rot (spreading from the base upwards)! Our optimised method, therefore, helps you transition from recreational hits-and-miss watering, to sustained precision, and avoid the frustrations of over or under-watering crops, along the way!
Myth 4: Deeper soils are more nutrient rich
People often suggest that deeper soils can provide a plant access to a greater range of nutrients than shallower soils. This is due to the fact that the plant might reach a range of nutrients at a greater depth in the soil profile, some of which may not available in as high quantities in shallower soils. However, there is an abundance of other, complex factors that interact to determine nutrient quantities and ranges.
In raised containers, like water quantities, nutrient concentrations can be easily monitored, maintained and optimised. Growing media is clearly measured, and exact quantities can be bought and used to fill your containers. The correct nutrient concentrations relative to the soil volume can also be measured and maintained, with correct ratios and volumes easily matched to your particular choice of crop. What’s more, these specific soils can be bought and mixed cheaper than in an allotment or large raised bed, as less soil is required to sufficiently fill a raised container!
Ergrownomics provides all you’ll need to do just this. We provide each of our planters with perlite, excellent for drainage and soil aeration, and additional quantities can also be purchased from our shop. As well as this, customers also get lifetime access to our soil preparation guides, developed by our on-site scientists to help recognise your existing soil type, and better prepare it for your growing needs!
Myth 5: You need to mix and match your crops in raised planters
A lot of popular, recreational raised planters are made in a “trough” shape. That is to say, that the edges of the soil are shallower than the middle. Again, while the design is common, it does involve some severe limitations! Given this variation in soil depths (and the inferred need for deeper soil depths in the chart above), gardeners are encouraged to take a ‘mix and match’ approach to their planting. Deeper root vegetables are regularly planted in the middle, with shallower leaves placed at the sides.
Our experiments have found these tapered soil depths extremely limiting to growth and yield. What was apparent from the studies was the need for a uniform depth, in which identical rows of the same crop could thrive. Our containers have a flat base, which allows for exactly this, emphasising productivity and uniformity – and refusing to compromise on standards!
This means that you can grow rows of crops, safe in the knowledge that none will be individually disadvantaged by a constricted, shallow growing media. A better yield and more enjoyable growing experience naturally follow. Our container is available in six basic colours, as well as in fully recycled black. Moreover, because it’s rotationally moulded in the UK, our container features smooth inner surfaces meaning that there’s nowhere for pests and diseases to hide! At Ergrownomics then, we have combined a clean contemporary style with all the practicalities and technical innovations that pedological research can bring.
So, what can we conclude?
It would appear then, that when beginning to consider using raised beds, planters and container in your garden, there are many important factors to consider, and the word of root depth charts should be taken with a sceptical pinch of salt!
To recap, the true most important factors that determine how successfully you can grow in a raised planter are:
- Chosen crop variety
- Maturity at harvesting
- Moisture supply
- Quality of growing media
Ensuring that all these variables are addressed will mean that you’re well on your way to producing high quality crops in your raised planter– and remember – our planter was designed with exactly these in mind!
Additionally, we recognise the need to provide an updated guide on crop varieties and desirable maturities, so as to fully offset root depth being a limiting factor on growth. So, look out for future posts on this topic! We hope you’ve found this useful, why not check out our planter to see what it offers, and feel free to get in touch if you have any questions!
Ben Carter, Ergrownomics Blogger