Selecting the right substrate for hydroponic berry production.

Substrates Used for Intensive Berry Production

 

IMG_2119 Figure 15 Nicky Mann with Jacco Hoogendoorn. (Source: W. Mann Legro The Netherlands March 2015)

What is a substrate?

A substrate is the substance or media in which the plants or organisms grow.  In the greenhouse industry substrates refer to products which are mechanically altered either by heat, chopping, treating, washing, etc. to produce an insert substance which can be used successfully to grow plants hydroponically where all the water and nutrients will be dosed according to the needs of the plant and the stage of development.  There is a multitude of substrates utilised to grow berry crops and they vary greatly.  Substrates normally have good moisture retention properties, high air porosity and a density to offer support to the roots to anchor the plant in a vertical position.  For the purpose of this report the following have been selected to evaluate.

Why use substrates?

The use of substrates such as coco-peat, rockwool and others has emerged to enable growers to cultivate berries in regions where the soil is unsuitable for berry production. For example in some parts of Chile, the soil pH is too high and there is a lack of ericaceous mycorrhizae (Gough, 1994) for the successful cultivation of highbush blueberries.  This is also the case in the Algave region of Portugal where the pH of the soil can be as high as 8.5, which makes it impossible to cultivate blueberries, raspberries, strawberries and blackberries. (Hugo, 2015) The growers here have adopted substrate production to enable them to utilise the positive climatic conditions of the region to produce berry crops where the pH of the soil would previously have been prohibitive.

Growers can select and combine specific formulations of substrates, which are ideal for the particular berry variety they have elected to produce.  Control over the nutrients and watering added to this carefully selected substrate can be precise and measured for the climatic conditions, the plant’s needs and stage of growth or development.  Substrates eliminate the need to worry about variation of soil type and structure within a cultivation area. This consistency makes the management easier and more refined, resulting in even crop growth, health and production.

Propagation Mixes

Berry plants require different nutrients when they are younger and have developing roots.  The propagation mixes tend to be finer to encourage the early root development and the uptake of necessary nutrients.

Sand

The majority of the main berry producing countries like Spain, Portugal, Morocco, Peru, Chile, Argentina, Mexico, California in USA are growing blueberries, raspberries and blackberries extensively in sandy soils.  The sand is usually sterilized with chloropictin or some other soil fumigant before use.  These soils are free draining, easy to sterilize[1] and fairly easy to add nutrients too – however, irrigation has to be regular to keep the plants from drying out and going into stress.

Blueberries in peru

Figure 16  Southern Highbush Production of Blueberries in Sand in Peru. (Source. World Berry Congress, Rotterdam March 2015)

Sawdust

There is a large company in New Zealand utilizes sawdust as a growing media for hydroponic blueberries and with significant results.  However, with the crop being relatively young it is hard to determine how the results will continue to be into the near future of 3-5 years time and whether the sawdust retains its structure or collapses and thus inhibits growth and ultimately yields.  However, using sawdust from pine trees may provide the blueberries with the acidity they require and hence the success at the moment.

Pine Bark

Pine bark is used by some growers for blueberry production and this media can provide acidity which the blueberries thrive in – depending on the size of the bark and its source – it can create difficulties for the growers as the density and porosity of the chips of bark can vary greatly and create issues with limited permeability to the feeds or releasing the feeds back to the rootzone at inconsistent intervals causing fluctuations and difficulties associated with control of the rootzone.  Some berry growers to use pine bark as an effective mulch on top of other substrates like coco-peat to deter weeds.

 

Coir

Coir is also commonly known as coco-peat and is made out of the mesocarp of coconuts – this fibrous waste material is left to breakdown and decompose for approximately 7 years before it is put through a process to mill it up.  The size of the milling or chopping process will define the size of the end product.  Below are some photographs to show the varying sizing of the coir from very fine dust to Fraction 1, Fraction 2 and finally Fraction 3 which is obviously a lot coarser.

Coco-peat stood out from the other substrates for intensive berry production for the following reasons:

  • Exceptional capacity for absorbing and distributing water,
  • Shows virtually no degradation, making it more stable than other organic substrates,
  • Retains its good drainage capacity longer than other substrates,
  • Coco-peat’s high air percentage caters for rapid root development,
  • Coco-peat is highly stable and is not modified by nor does it modify the soluble nutrients and fertilisers applied to the plants,
  • Renewable form of growing media
  • Totally biodegradable when it is no longer needed for growing purposes,
  • Trichoderma is naturally contained within coir, (Hoogendoorn, 2015)
  • Could be easily blended with Irish peat, perlite and bio-stimulants for optimum results,
  • Adaptability – the size of the coco-peat can be selected, from fine to coarse and anything in between, and
  • Coco-peat fibres facilitate excellent lateral water distribution for the benefit of the berry roots.

 

It was interesting to observe at Haygrove UK that 95% of their berry fruit production is in substrate (mainly coco-peat) and in the last 10 years there has been a 50% increase in production due to improved varieties and the use of substrate.  There has also been a significant increase in class one quality fruit due to the new production systems.  The owners realised that land is in short supply so had to utilize the area already owned and under production to produce more using substrates and tunnel cultivation.  (Laura, 2015)

Faction 3 is big particles of coir and used for strawberries

Faction 2 is medium particles of coir and used for blueberries

Faction 1 is small particles of coir and used for smaller plugs, potting mixes and propagation mixes

Dust is not commonly used in mixes as the fine particles tend to sink to the bottom of the container and create a wet sludge which is not beneficial and usually encourages root borne diseases to develop.

 

IMG_1959Figure 17 Coir showing Fraction 1 on left and Dust on right. (Source: N Mann Legro The Netherlands April 2015)

IMG_1960Figure 18 Coir showing Fraction 2 on left and Fraction 3 on right. (Source: N Mann Legro The Netherlands April 2015)

IMG_1942

Figure 19 Coir Fibre ( Source: N Mann Legro The Netherlands April 2015)

The fibres can be cut up in to varying sizes too but should always be included in the coir blend as the fibres assist with lateral movement of water in the substrate which assists with even water distribution within the container.  There is an advantage of putting more fibres into a raspberry blend of coir for more lateral water movement and uptake by the vigorous root activity of these plants.

It is recommended to maintain a consistent particle size in the substrate used by hydroponic production of berries as this limits the finer/smaller particles sinking to the bottom of the container. The thick, coarse pieces of coir like the chips in a blend may be problematic as they absorb the nutrients from the fertigation feed and then release it at random intervals at the chip breaks down – this can be frustrating and confusing for a grower as the release of different elements can modify the rootzone and what is available to the plant other than the nutrients recently delivered in the latest feed. (Hoogendoorn, 2015)

Peat Moss

The Swedish and Baltic peat moss comes from the green sphagnum moss whereas the Irish peat moss is derived from the red sphagnum moss which makes it dark and heavy with excellent structure.  The peat is mined and is not a renewable source of growing media.  However, there are great advantages of using peat moss as a growing media especially for berry crops.  In The Netherlands, one highly successful raspberry propagator uses a combination of Irish Peat Moss and Coir with a mycorrhizae additive for exceptional rooting results.

IMG_1956

Figure 20  Left to Right: Swedish, Irish and Baltic Peat Moss. (Source: N Mann Legro The Netherlands April 2015)

Many blueberry growers are using peat moss in their blends for added acidity and structure for the blueberry roots which do not have root hairs.  There are some growers advocating the addition of Peat Moss with the coco-peat as the Irish Peat has more structure, lasts longer and offers the plants an extended growing period in a containerized hydroponic system.

Vermiculite & Perlite

 Vermiculite is one of the world’s most unique minerals. A hydrated Magnesium Aluminium Silicate, it is lightweight, inorganic (incombustible), compressible, highly absorbent and non-reactive and is used in various of applications including potting soils and grow mixes. (Australian Perlite)

Perlite is the generic name for naturally occurring salicaceous volcanic rock, it is beneficial to add to a coir blend especially for blueberries (Hoogendoorn, 2015) or any berry crop which is going to be grown in the same media for an extended period of time as it is very stable, has excellent moisture retention but does not hold fertigation solution or individual elements.

Blends and Combinations of Substrates

Blends and combinations of substrates show the most promise for intensive production of berries in hydroponic systems as the media can be precisely selected for the best outcome for the plants.  For example, SH Blueberries flourish in acidic root conditions so using a mixture of Irish peat moss, coir, perlite, mycorrhizae, buffered to the correct pH  and charged with nutrients for the plants to commence growing immediately with a layer of bark on the surface as a mulch would be ideal.

Rockwool

Rockwool is a volcanic rock heated to extreme temperatures to fluff it out and it has been used in hydroponic systems for many years and is extremely popular with some growers as they feel it is the best media available for the following reasons:-

  • Retains water
  • Purity
  • Holds air
  • Convenient sizes for growing in
  • Clean and convenient

Mark Massey from Greenworks says “whatever you do with rockwool multiplies itself, so if you get things right, the yields, the quality and plant health will be optimum and nothing compares to this media for precision.  However, if the grower gets it wrong – the results can be disastrous with rockwool as it is not very forgiving.”

However the following disadvantages need to be considered too:-

  • Not environmentally friendly and hard to dispose of
  • Dust and fibres are a health risk
  • pH is naturally high which requires adjustment by the grower

Buffering of Substrate

IMG_1941

Figure 21  Bulk Buffering of Coir. (Source: N Mann – The Netherlands April 2015)

What is buffering?  It is washing out the excess salts that are naturally occurring in coco-nut husks.   This is vital because the salts (sodium and potassium) are bound within the cells and if they are not washed out and if you add calcium or magnesium to the coir to feed the plants these salts are released and inhibit the plant growth.  So once the salts are removed the substrate can be charged with the right base nutrient make-up to start using in a hydroponic system.  Ready-buffered coir provides a big advantage to a grower as they can put the coir straight into the containers and plant the berries and starting applying normal nutrient feeds and growing the berry plants as normal.  As opposed to receiving the coir – having to tediously wash it and then charge it will base nutrients so that it is now useable for growing anything in it.  The ratio is normally 1 cubic metre of coir to 1 cubic metre of water for buffering and washing of the coir.  There after it is charged with calcium nitrate depending on what crop is going to be grown in the media.  This saves the grower time and in bulk buffering is done with precision over a huge volume of media.

Mycorrhizae and Trichoderma

Both these fungi are showing great potential in the berry industry as they form symbiotic relationships with the plants by increasing the uptake of nutrients by the roots.

In blueberries especially, Ericoid mycrorrhizal fungi helps them prosper in poor low pH soils, low in nitrate and calcium but high in organic matter. (Hancock, 2012) Most of the colonization occurs in the top 15cm of the soil.  In a study of container-grown blueberry bushes inoculated with mycrorrhizae 6 out of the 7 cultivars increased total plant biomass. (Scagel, 2005).  It was also noted that in highbush blueberry cultivars that fruited early in the season had higher levels of colonisation of mycrorrhizae in the root system than those that fruited later in the season. (Yang)

In strawberries, arbuscular mycorrhizal fungi is beneficial and has great water saving properties.

However, in hydroponic systems with good feeding programs these fungi may not be necessary as the plants are being administered exactly what they require.  Although it is recommended that these be included in the base mix in the beginning to give the plant every advantage in the early plant development stage.  Trichoderma is naturally occurring in coir. (Hoogendoorn, 2015)

Suppliers of Substrate

There are a vast array of substrate suppliers and most of them are now offering specific berry blends for specific berry crops.  Make sure it is buffered.  When coco-peat is RHP certified this is a very high standard product that has been certified in The Netherland & proves the product is exactly what it claims to be.

Top suppliers are: Legro, BVB, Jiffy, Galuku,

[1] With phase out of Methyl Bromide sterilizing all soils including sand will become more prohibitive.

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