Quadgrow Self-Watering System - Part 2 (Set-up)


Polytunnel - 3rd August 2021

In the kitchen garden, I have a 3m x 4m polytunnel supplied and erected by Haygrove in Spring 2011; this will be its 12th growing season.

I used a mix of direct soil planting and growbags for the first four growing seasons but then switched to the Quadgrow self-watering system, pioneered by Greenhouse Sensation, for the 2015 season. It started with a couple of Quadgrows and has gradually developed over the years to include both medium and large Salad/Veg Planters as well.

I had wanted to convert to a hydroponic (soil-less) system such as the Vivogrow but I didn't have a power source in the polytunnel so opted for the cheaper self-watering system. Solar-powered hydroponic systems have since become available, but I was already invested in the Quadgrows.

Currently, the polytunnel is set up with four 4-Pot Quadgrows for tomatoes and cucumbers, two medium Salad/Veg Planters for aubergines and chilli peppers, and three large Salad/Veg Planters (one for sweet peppers, one for all the 'straggler' plants left over after the best ones have been potted-on while the third planter is part of a new compost trial for one of my suppliers). This year I have decided to grow salad leaves, lettuces and radishes in outside Salad/Veg Planters rather than in the polytunnel as I normally do. In addition, I am also growing celery and celeriac in three large Salad/Veg Planters (outside) and, of course, the new Bog Garden is in a medium Salad/Veg Planter.

The Quadgrow self-watering system comprises a bottom reservoir (for the aqueous nutrient solution) on which sit four 12-litre pots that hold the growing medium. Connecting the reservoir and growing pots is a length of capillary matting that draws the nutrient solution up into the growing medium.

At the beginning of May, I set up the 4-pot Quadgrows as follows:

Step 1: Place the reservoir base in position using a spirit level to ensure it is level

Step 2: Fill reservoir with nutrient solution

Step 3: Add the reservoir cover and place the 12-litre pots in position

Step 4: Prewet the supplied capillary mats and feed through the holes in the bottom of the pots so that most of the matting is in the nutrient solution

Step 5: Prepare the growing medium. I use a coir-based medium mixed with perlite but there are plenty of other options. The growing medium does not need to contain plant nutrients as these will be supplied via the reservoir. Low-nutrient seed compost is fine but I prefer to make my own. I buy 5 kg organic coir bales (£9) and 100 litre bags of perlite (£30) from Fertile Fibre, a local Herefordshire company. After rehydration, each 5 kg coir bale makes about 80 litres of growing media which is mixed 4:1 by volume with perlite: cost about £15 for 100 litres. 

(i)    Put coir block in a large trug/bucket, fill with water and go & find something else to do for 15 minutes...

Rehydrating 5 kg Coir Bale

(ii) Repeat two or three times until the coir bale is sufficiently hydrated and swollen to enable segments to be broken off with your hands (an old screwdriver is useful for separating the layers)...

Partially Rehydrated Coir Block 

(iii) In a separate container, add more water to the broken-off segments and leave for 30 mins to an hour for the coir to rehydrate fully. Rub the coir between your hands to ensure it is evenly rehydrated and there are no dry portions.

Broken off Segments ready for Final Rehydration Stage

[Note: Any fibrous parts (long strands or clumps) that do not hydrate properly can be removed (for seed compost) or just left in for potting compost. A soil sieve is useful for removing any strands or clumps if you need to - just run the rehydrated coir through the sieve]

(iv) Measure 8 litres of rehydrated coir into a trug or similar container and add 2 litres of perlite...

Rehydrated Coir & Perlite Before Mixing

...before mixing well by hand (I usually wear gloves)...

4:1 Mix of Rehydrated Coir and Perlite

Step 6: Pull the well-soaked capillary mats partially out of the reservoirs and fill the pots with the prepared (or bought) compost. A small part (2-3 cm) of the capillary matting should stick up above the compost in a corner of the pot...

Filling Quadgrows with Compost - end of capillary matting just above the surface

Step 7: Leave overnight to settle and add plants the next day!

Quadgrow planted up with Tomato (x3) and Cucumber

If cold weather or cool nights are forecast then add a Quadgrow 'mini-greenhouse'. Once the plants are big enough, add a mulch cap to reduce surface water evaporation and restrict algal/weed growth.

A month later, the plants are settled in and starting to put on strong growth despite May being on the cool side. The cucumbers really need warmth to bring them on so my specimen, in the right-hand corner, is yet to start its rapid growth phase. Nevertheless, a few days later we were enjoying our first cucumber of the 2022 season.
Plants settling in

Tomatoes and cucumbers will need support. The current Quadgrow system (post 2018) comes with built-in cane support, which my older units do not have.  So I build a framework out of aluminium poles bound with flexible tie. The flexible ties are reuseable - some of mine are in their 10th year of use.

As you can see from the photo, I have installed a holiday watering kit - the 100-litre water butt feeds two 4-pot Quadgrows.

100L Water Butt feeds Two 4-pot Quadgrows

Simply fill the water butt with the nutrient solution and you can leave the plants for between one week and four weeks depending on the temperature and size/development of the plants (e.g. cucumbers need a lot of water to swell up and ripen but relatively little during their early growing stage).

I use the Nutrigrow plant food sold by Greenhouse Sensation - specifically, the refill packs...

Nutrigrow Refill Packs

Every Quadgrow bought from Greenhouse Sensation comes with enough Nutrigrow for the first growing season. Keep the original plastic bottles so that you can refill them, using refill packs, for subsequent growing seasons. 

The nutrients come in two formulas (A and B) that are mixed to provide the correct nutrient balance for the Quadgrow system. Each refill pack (250 g) is made up to 2.5 litres with tap water in the original bottle. Using a 100 ml plastic syringe, I add 60 ml each of the A & B solutions to a 10 L watering can and fill with tap water. Pour into Quadgrow reservoirs or water butt if you have the holiday kit.

Nutrigrow A & B Nutrients

Regrettably, Nutrigrow is not an organic fertilizer which would be my preferred choice - I understand the reason is that soluble organic fertilizers (based on seaweed extract?) start to decompose and smell after about 24 hours so are not really suitable for the Quadgrow system. Approximately 50% of the world's population is fed because of artificial fertilizers so I comfort myself in the knowledge that (i) these inorganic fertilizers are a necessity to feed the world, and (ii) I am also using them in a the most efficient way - just enough to grow my plants and none of it escapes into the environment.



  1. Hello,
    I wonder if you could help me with the following, please?

    Now that Greenhouse Sensation is no longer trading, do you know of any viable alternative to their Nutrigrow fertiliser that they sold for use with the Quadgrow system?

    Any help or advice would be gratefully appreciated,

    Kind regards,


  2. Peter,
    Thanks for your comment. I must admit I wasn't aware that Greenhouse Sensation had ceased trading although the website suggests, maybe, a temporary rather than permanent halt. In broad terms you need to look for hydroponic plant nutrients. For example:
    Hydrocrop Soluble Dry Powder Complete Hydroponics/Coco Nutrients Plant Fertiliser Feed (500g each HydroSol A & B).
    This is available on Amazon and possibly elsewhere. It has a broadly similar composition to the Nutri-grow and used in exactly the same way: i.e. two separate stock solutions that are mixed and diluted.
    As I have only just come across this problem, I will spend a little more time looking for other alternatives.
    Best Wishes,

  3. Morning Ian,
    Thank you for the quick reply and the information provided, its appreciated.
    I only found your blog by chance, while searching for information on the Quadgrow.
    I will go and read up on your suggestions.
    I would be interested to know if you come up with any other alternatives, however i don't really want to put my email address on here.


    1. Peter,
      Absolutely fine with you not posting your e-mail. I'll post any updates here.
      I have contacted Greenhouse Sensation (GS) directly and will be interested to see if there is a response. Also contacting Nutrigrow to see if there is an option for them to supply directly. My understanding is that the plant nutrients were formulated specifically to a GS recipe.
      I have found an alternative, Chempak, available from a number of suppliers. I just need to confirm NPK values for the various options they offer.

    2. Thanks, Ian, some interesting information there.
      I am sure that I read on one of the forums that GS had gone into administration which is a shame because I wanted to buy one or two Quadgrows. If they are not coming back, I will DIY something. I have a few ideas.
      Is there any way I can get notifications regarding replies to your site?



    3. Peter, you may be correct regarding GS going into administration. I've not heard anything from them yet.
      My son set up the blog so I will have to ask him about notifications. Good luck with your DIY alternatives.

    4. https://www.allotment-garden.org/garden-diary/8064/greenhouse-sensation-replacements/ confirms Greenhouse Sensation has gone into administration.

    5. Thanks for the reply, Ian. Yes, and a shame they have gone into administration.
      Please let me know about possible notifications. I would like to see how you get on regarding Nutrigrow and the best alternative.


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