Green City Gardens

When I first got into gardening I always liked the idea of growing edibles and, like many people, started with a few tomato plants in growbags in the back yard.  Although we now have an allotment I still prefer to grow a small amount of produce at home in our tiny back garden which is sheltered and south facing, and so ideal for outdoor grown tomatoes (and chillis).  There’s also nothing quite like being able to pop out of the kitchen and pick a few just ripe tomatoes to gobble up straight away.  I’ve always liked to try different cultivars, and frequently find myself beguiled by those which are quirky colours or otherwise a deviation from the standard red salad tomato you find in the supermarket.

Earlier this year I read James Wong’s ‘Grow for Flavour’ which is full of interesting approaches to getting the best from your home grown crops and made me realise that perhaps my usual criteria of ‘which cultivar is weirdest’ wasn’t necessarily serving me that well!  Amongst his advice on how to maximise the flavour of your home grown toms (apart from choosing the right cultivar) were:

• grow tomatoes in soil rather than a container of compost because they will have access to a wider range of nutrients
• feed them with Potassium-rich molasses rather than the usual proprietary tomato fertiliser which is higher in Nitrogen
• spray them with aspirin (something to do with mimicking plant hormones)

I did none of these things due to a mixture of cost, convenience and time factors, but what did pique my interest was the advice on pruning tomato plants to maximise both yield and flavour.  Essentially, rather than the traditional approach of allowing a plant to form 4-5 trusses of fruit before pinching out the top, plants would be stopped at one truss of fruit.  In theory this should mean plants can be positioned closer together, would not need staking and would allow the plant to focus all of its attention on producing one truss of large, flavoursome fruit.  So this I thought I’d have a go at.

The Methodology

For 2018 I grew three varieties of tomato from seed:

• ‘Gardener’s Delight’ – a red cherry tomato generally regarded as a garden favourite
• ‘Black Opal’ – a dark red cherry tomato
• ‘Zlatava’ – an orange salad tomato which has red flesh a bit like a blood orange

One plant of each variety was grown in the traditional manner, in a pot supported by a bamboo cane, side-shoots removed and pinched out at four trusses.

Four plants of each variety were grown in large planters, spaced 20cm apart, side shoots removed and pinched out after one truss had formed.

Otherwise all plants were treated the same: raised from seed on an indoor windowsill, hardened off in an unheated outdoor growhouse, planted outside in containers of compost, watered regularly and fed with Tomorite liquid fertiliser every 1-2 weeks.  In this way I wanted to see how the yield from four trusses on a single plant compared to four trusses from four small plants.

Growing Pains

Perhaps because the weather was very cold well into Spring, and therefore seedlings were kept inside for longer than usual, my tomato plants were quite ‘leggy’ i.e. elongated rather than the more desirable shorter, stouter and bushier.  Not to the point that they were beyond salvation but certainly more than ideal.  The consequence of this was that the single truss plants were taller than expected by the time the fruit had formed meaning that they did need staking and were probably planted too close together for their size.  By the time they were laden with fruit later in the summer they were in fact a bit of an unwieldy mess – more triffid than tomato!

Little and Large

Fruit was harvested over a period of approximately two months between mid-August and early/mid-October.  Impressively, for both the ‘Zlatava’ and ‘Black Opal’ cultivars the yield by weight from the four single truss plants was approximately double that from four trusses on a single plant pruned in the traditional manner.  For ‘Gardener’s Delight’ there was little difference in yield from the two different pruning approaches.  The results are depicted in the visualisation below provided by my partner in crime, Datawoj.

In the case of ‘Gardener’s Delight’ and ‘Black Opal’ the fruit also ripened earlier on the single truss plants than on the traditional four truss plants, whereas in the case of ‘Zlatava’ the first ripe fruit appeared at around the same time on all plants.

So on the evidence of this little experiment changing the approach to pruning tomato plants certainly seems to have quite a significant impact on yield, though perhaps it is slightly dependent on the chosen cultivars.

Comparing Cultivars

Some outcomes for the different cultivars:

Yield:

• Highest: ‘Black Opal’
• Lowest: ‘Gardener’s Delight’

First ripe tomato:

• Earliest: ‘Gardener’s Delight’
• Latest: ‘Zlatava’

Proportion of overall yield which ripened by early/mid-October:

• ‘Gardener’s Delight’ – 96%
• ‘Black Opal’ – 93%
• ‘Zlatava’ – 61%

For all cultivars a higher proportion of the yield ripened on the single truss plants than on the traditional multiple truss plants.

Overall evaluation:

 

• ‘Black Opal’ was the best of the three both in terms of the yield and timely ripening and on the basis of the all important flavour which was a good balance of sweetness and bite.
• ‘Zlatava’ provided a good yield and decent flavour but a much higher proportion remained unripe as the season came to its end so perhaps not the best choice for outdoor growing.  That said it did provide the bulk of the fruit for the old store cupboard staple of green tomato chutney so it’s not all bad!
• ‘Gardener’s Delight’ was disappointing, particularly given its reputation as a reliable garden favourite.  Perhaps this bears out the results of the recent RHS plant trial for cherry tomatoes which found the seed stock for ‘Gardener’s Delight’ had become diluted resulting in it losing its Award for Garden Merit (AGM).

Where do we go from here?

In terms of the approach of restricting tomato plants to a single truss, the positive impact on yield in this little back yard experiment is hard to ignore and I certainly would not rule out doing this again. One of the claims made by James Wong for this approach is that you can get the same or better yield from the same space as a traditional 4-5 truss plant, but this I am less convinced by. Extreme weather conditions notwithstanding, my single truss plants were over-crowded when spaced only 20cm apart so I think in reality a larger growing area would be required. There’s also the fact that you need more plants, though this could invite the opportunity to grow a wider variety of cultivars in any given season. So there pros and there are cons.

What is certainly clear is that choice of cultivar is of major importance to the timing of cropping and overall yield as well as the holy grail of maximum flavour. So I shall try and resist the temptation to choose seeds on the basis of what wacky colour of crop they produce and more on suitability for outdoor growing and promises of flavour.

Whatever choices I make I know that I’ll enjoy continuing to experiment with my edibles growing for years to come.