Heating a Greenhouse With Compost : Pt 8

Part 8 Posted on 23/06/2013. Click here for the full sized original post.

“Entomological Explosion; Growing Tomatoes Organically in a Garden Greenhouse (Heating a Greenhouse with an External Compost Bed- Part 8); and Egg on Your Face.”

Almost exactly a year ago the same issue seems to have preoccupied my gardening notes. Midges. After several days when midge numbers increased daily to the point that I had to use a deterrent spray, I’d wandered outside first thing. Glanced up at the cloud cover. Felt the warmer morning temperature, and lack of breeze on exposed skin. And feared a terrible day.SDIM1388 (4)

And then I waited and waited, whilst bent double re-weeding the garden’s newest and hence sparsely planted areas, for the bites to begin. And none came. I can only assume that a first generation of adults, emerging after warmer sunnier weather a couple of weeks ago had all reached the end of their life at a similar time. This benign situation lasted barely a couple of days, since the return of warmer conditions triggered a second wave of vicious biters within 48 hours.SDIM1483 (2)

But such conditions also favoured a huge explosion of insect activity in the garden as the Cotoneaster horizontalis flowered…SDIM1414 (2)and several insects which have been seen rarely, if at all before, presented themselves for photography…SDIM1507 (2)SDIM1512 (2)SDIM1544 (2)SDIM0996 (2)SDIM1596 (2)

Back in April I gave what I then said was going to be my last update on ‘The Reactor’ – my design for heating a greenhouse with an external compost bed/heap. In fact I think it’s appropriate to give an update now, for 4 reasons :

  • Firstly to report on the ‘compost / leaf mould’ yield and quality, since a fair proportion of the material has now been dug out. And to record it’s use. SDIM0105 (2)SDIM0111 (2)
  • Secondly to record how the various crops are performing now that we’ve just passed the longest day. (Image below taken on 16/06/2013)SDIM1458 (2)
  • Thirdly, thanks to a near neighbour who has been growing similar plants in a similarly sited (i.e. South facing but less shady) poly tunnel, I have a primitive comparative control. Many thanks to Dave for letting me include these photos of his set up and plants taken on 19/06/2013. The blue structure is not a swimming pool under construction! But rather Dave’s own version of an external insulated compost bed to heat his poly tunnel for the coming season, having been sufficiently impressed by my efforts to have a go himself this autumn. Dave has calculated that this much bigger sized heap should produce up to 1.8 KW of heat when its up to speed! The blue material is ‘second grade’ boarding of a type of building polystyrene with considerable strength and water shedding properties – a much better bet I think than the Celotex insulation boards which I used, and having rebated edges and being 140 mm thick, it also has double the insulating ability of my 70 mm boards, and is simple to put together … SDIM1578 (2)SDIM1582 (2)SDIM1583 (2)SDIM1580 (2)SDIM1585 (2) … (the fruit trees are the same ‘Tomcot’ apricot and ‘Lord Napier’ nectarine that we grow in the greenhouse, and were planted at the same time. The tomato plants were seedlings I saved from ‘Real Seeds’ cherry tomato selection, and were passed on at the 3 inch pot stage) …
  • And I can also provide a link, by clicking here to Nick, an amateur but experienced UK garden tomato grower, who happened to post a video of how his tomatoes are performing in a polytunnel at about sea level in Birmingham (?) – Dave and I are both about 800 feet above sea level – on June 21st , a couple of days after my photos were taken.
  • Fourthly, because although most of the compost has been dug out, I’ve retained the section around the inner spiral pipe, and have kept the fan circulating air through the heap on an intermittent basis.SDIM1608 (2)Why?
  • Researching all the issues concerning greenhouse tomato growth (which is my planned for principal greenhouse summer crop along with nectarines and apricots) makes you realise just how complex achieving optimum conditions in an amateur greenhouse can be. There are just so many variables – variety grown, maximum and minimum temperatures, humidity levels, growing substrates, fertiliser used and frequency of application, light and shading issues, space per plant, degree of ventilation, frequency of pollination, frequency of watering, etc, etc. But after just 2 previous years’ attempts, I can confidently say that my efforts this year seem vastly more successful (so far) than previous years in spite of the very slow late spring.SDIM1662 (2) … (Tomato ‘Black Cherry’ on 21/06/2013)
  • Comparisons with the nearby poly tunnel make both Dave and I think that one of the key factors is a more even 24 hour temperature range in our greenhouse with warmer nights, and also being able to limit peak temperatures on sunny days. In this respect the partly emptied compost bed with air still being circulated through the reactor’s central spiral pipe may still be playing a helpful role by acting both as an additional heat store for the night time and perhaps also adding an extra level of Co2 to the atmosphere. Commercial growers are well aware that low atmospheric Co2 levels can stop tomato plant growth surprisingly early in the day, if steps aren’t taken to introduce more Co2 into the greenhouse environment, once the plants are getting larger.

Click here for a link to a successful commercial UK grower’s solution to this issue. Chris Wall, whose ‘Sophie Jane’ tomatoes we have eaten recently from a local superstore, counter intuitively fires up his boilers during the summer daytime, to provide additional Co2 for his tomatoes, whilst storing the hot water produced to recirculate into the greenhouse at night to raise night time temperatures, and avoid a big temperature drop. 

The ‘compost’  from the bed has been used for potting on seedling tomatoes, cucumbers and peppers (this will be my last year to attempt peppers if they don’t perform, since growing them successfully seems quite tricky compared to tomatoes), and latterly courgettes and squash. It was used as it came out of the heap without any sieving but was mixed about 50/50 with garden soil for the tomatoes, though it was used as was for the courgettes. Is there a distinction between my ‘compost’ which was largely made with chopped leaf material and added nitrogen (pee and chicken or sheep manure), and ordinary leaf mould? Most gardeners consider them to be very different materials.

In both cases the mix was kept really loose, and what surprised me after potting on from the initial 2 litre pot into the final bag or larger pot was how exceptionally healthy the root systems seemed to be compared with previous years when much denser soil from the garden was used.

I guess that the more open material allows much more root oxygenation as well as better drainage. And a lack of oxygen at root level can certainly limit plant growth and affect mineral uptake. I’m now thinking about redesigning growing containers/beds next year to try to take account of this need for root level oxygenation. Although I had concerns that material straight from the heap might still be too nitrogen rich for normal growth, to date the plants seem happy.

  • SDIM1453 (2)
    Another really interesting resource on optimal conditions for greenhouse tomato growing which I’ve just discovered is a PDF ‘Greenhouse Tomato Book ‘ produced

by Dr. Richard Snyder for Mississippi State University. Although directed at commercial growers in a very different climate to upland Wales, many of the growth and cropping limiting factors are discussed in a very clear, if detailed, way. Click here for this link.

  • My current routine for the now flowering tomatoes includes:
  • After raising the seed in a tray of seed compost (bought in this year) placed on a heated pad in the greenhouse, the plants were potted out into 3 inch pots with a 1 cm layer of part rotted sheep bedding/manure at the base of the pot, compost being added above this.
  • The plants were potted on into 2 litre pots when the roots were showing from the base of the 3 inch pots.
  • The plants were moved on again into their final pots (about 12 inch diameter) when roots were showing at the base. These are placed on the greenhouse border soil. At this stage some of the early varieties had their first flower trusses visible.
  • Soaking the central heat store path in the morning and possibly after pollination to raise humidity and also to help limit maximum temperatures on sunny days.SDIM1601 (2)
  • Pollinate with the vibrator every other day. I still tend to ‘vibrate’ every individual flower (Click here for explanation) although apparently just vibrating the whole truss for half a second is probably adequate according to the tomato handbook. Pollination is more successful around midday when humidity is lower and consequently pollen grains are less sticky, and more mobile. So delay a second hose down until after pollination.SDIM1631 (2)
  • I’m still experimenting with watering frequency, and what to use in the way of nutrient. The above Tomato Handbook shows rising levels of nitrogen in the feed as the plants begin to set trusses – I always thought that UK gardening convention was to switch to low nitrogen and high potash when the first flowers appeared. For now I’m using a teaspoon of wood ash and a dash of pee into a 2 gallon watering can, and doing this about once a week with an alternate watering with plain water, as an aid to avoiding over supply of nutrient. So you can see that with no bought in nutrient or compost the tomatoes really will be home grown. SDIM1610 (2)
  •  Having enough stored water in 5 gallon containers to allow all plants to be watered with water which has been warmed by the greenhouse environment for at least 24 hours. (Our spring fed hose water emerges from the tap really chilly and would give a considerable cold shock to the roots). According to Snyder’s figures a mature tomato may require up to 2.7 litres of water per day. So with over 40 plants to deal with, my 3 large containers are about one short, but a watering can full for about every 4 to 5 plants is fairly easy to judge. I’m using untreated spring water for this with a pH only just above 5. SDIM1600 (2)
  • I’m growing a few new heritage varieties, and other more modern forms this year. An immediately obvious issue is the speed of flower and first fruit formation from both ‘Stupice’ and saved seed from my ‘Real Seeds’ cherry tomato cultivar from last year. These are both at least 2 weeks ahead of  ‘Black Cherry’, ‘Black Krim’, ‘Piccolo’ and ‘Orange Banana’, and a striped tomato grown from seeds saved fruit bought from Tatton Flower Show last year. SDIM1554 (2) SDIM1553 (2) …(Saved Real Seeds cherry tomato and tomato ‘Stupice’ on 19/06/2013) …
  • Training some of the larger cultivars later in the year might present space issues, if they continue to grow in the same vigorous way they are currently growing. An awareness of how large the plant will get is quite important – all tomatoes aren’t the same, and I suspect that the larger growing cultivars would be better off in larger root containers.
  • The apex fan is now running pretty continuously from about 8 am to 6 pm pushing heated air below ground and into the stone filled central path heat store.SDIM1606 (2)The ‘Reactor’ fan drawing air through the compost heap is running about 20 minutes on, 20 minutes off through the day, and for a 2 hour slot from 11 pm to 1 am. Both are 20 watt rated and covered almost completely on most days by our PV generated electricity.SDIM1607 (2)
  • In spite of 4 Bayliss auto vents in the 14 X 8 foot ‘Woodpecker’ cedar greenhouse roof apex,SDIM1612 (2)I still need to open the door a variable amount every day partly to aid ventilation and Co2 levels, and partly to keep temperatures below the 35 degree C maximum. Above this level and plants will stop growing and can suffer nutritional issues with poor mineral uptake, as well as poor fruit set. 
  • I’m initially training them up Miscanthus giganteus stems saved from the garden last autumn, tied to overhead line wires and tying in new growth with pre cut Flexi-tiesSDIM1609 (2)  (which I hope to be able to re-use in future years, since its fairly pricey), and which seems to retain good flexibility over time.SDIM1603 (2)One of the points that Snyder makes is how much time cultivating tomatoes successfully indoors can take!
  • I’m gradually working out a routine which combines pollination, watering, refilling the 25 litre containers and tying in new growth simultaneously to avoid too much wasted time!

Recording maximum and minimum temperatures is really helpful.SDIM1670 (2) This shows the figures for the last 24 hours – a mainly grey cool drizzly day. Ideally the minimum would be a bit higher (low ’60′s degrees F). But on a sunny day before I started checking these readings, over 40 degrees was occasionally shown – this is far too high for healthy growth and fruit set. For me, apart from more frequent hosing of the central path, the extent to which I open the door is a good way of limiting maximum temperature during the day.SDIM1611 (2)

  • I always close it at night, but if we were away, I’d leave the door open since the risk of slightly low night temperatures is less worrying than too high day temperatures. 
  •        So I hope this update gives readers an idea of what I’ve learned about the compost bed heating system and my current experiences and thoughts on organic greenhouse growing of tomatoes in the UK in an amateur setting.
  • The poultry continue to fascinate.
  • The turkeys are still sitting on lots of eggs, presumably infertile, and our single hatched poult (Dora/ian) continues to explore to parental amusement, or is that annoyance? Or concern? …
  • SDIM1638 (2)
  • The 5 Light Sussex chicks are racing around and growing well…
  • SDIM1572 (2)
    •  I broke open the remaining egg, being abandoned by the broody hen, to find a dead but nearly fully formed chick inside. Did the mother know it wouldn’t be viable? Or did she just think 5 were more than enough?
  • SDIM1362 (2)
  • Meanwhile our remaining 2 hens have been wasting a lot of my time, with me trying to ensure that we have at least a few eggs for the kitchen. Why? Well smashed eggs had become an almost daily occurrence.SDIM1364 (2)We were pretty certain that one hen wasn’t laying at all, and had decided to cull her, since I’d eventually found her with egg on her face, and beak, and a broken shell in the laying box.SDIM1368 (2)But prevaricating was, for once, a good move since a couple of days later we had 2 eggs in a day, which confirmed that she had indeed started laying, and then I realised that her very noisy crescendo of  “Bok, Bok, Bok, Bok, BokkkAAAH” always coincided with her laying an egg. But often the second hen was sitting on it by the time I made it up to the coop. Leaving her be and checking for eggs later on still resulted in finding smashed eggs. I was beginning to wonder whether her laying call was attracting the attention of either the magpies or squirrels which still enter the runs for grain. Quite annoyed by the loss of eggs, I decided to shift the second sitting hen off the nest box to remove any egg that was there. This worked well on the first occasion, but the following day when I tried it, having removed one egg earlier in the morning, the hen was having none of it. As I prodded it off the nest box with a stick and the second egg of the day appeared from under her, she whipped her beak round and as my hand reached towards the pale brown shell smashed it with a single peck, the yolk and white quickly seeping into the bedding. Although it was her own egg, one sensed a certain triumphant “That’ll teach you” as she left the coop with a noisy Bok Ahh, Bok Ahh, Bok Ahh!
  • Cyril the cockerel is blameless, and rises above such affairs, as far as I can work out.SDIM1576 (2)But now both hens have tasted yolks, and I seem to be the one with egg on my face.
  • There don’t seem to be any simple cures for hens which attack their own, or other’s eggs. Culling is often recommended. Watch this space.
  •  Perhaps this situation is the real origin of the phrase ‘Egg on Your Face’. Maybe Cyril’s version of vigorous avian mating activity is also a clue to the origin of the expression of being ‘Downtrodden’?
  • . Since this indeed is what the poor hens suffer on a regular basis, resulting in quite a bit of feather loss from their backs… SDIM1574 (2)
  • Finally a few more images from the garden, including a bit of fun with some leached out daisy and primula flowers in a bowl of water …
  • SDIM1626 (3)SDIM1626 (4)SDIM1628 (2) SDIM1470 (2)SDIM1478 (2)SDIM1488 (2)
  • SDIM1393 (2)

    For some video of what the garden looks and sounds like in June, follow this link to some one minute clips on our new You Tube ‘ImpressionistGarden’ site…



  1. Wow! What a compendium of great photos. Even those with the pests look good. How do you see this passion for “growing stuff” serve you in future?


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