This year I’m trialling the new SylvaGrow Peat-Free Planter from Melcourt, one of which I was very kindly sent for the purpose, alongside a bog-standard 50% peat, 50% “forest gold” growbag (which happens to be from Bulrush).
So far the ‘Maghrebi’ tomato plants have all been doing well. I’ve been watering them as regularly as I’m able, feeding them once or twice when it seemed like they might be flagging a little – but perhaps not as regularly as maybe I should, as you’ll see below). Moving into the end of August, with fruit forming up but not ripening quite yet time, I decided it was to start helping them along a little.
Pruning to Promote Ripening
I started by trimming back the growing tips of the plants, both the top few inches of the main stem and the ends of all the foliage shoots. I then completely trimmed off a few of the lower leafy shoots from all four plants – keeping the amount of cutting-back as even and equal as possible.
This is the general advice given to tomato growers in most books and magazines (and I think Carole mentioned it in this week’s episode of Beechgrove) and earlier this year, as part of my RHS Level 3 studies, I learned the science behind the plant’s response. The short version is that cutting back the growing tips removes the main sources of production of the plant growth regulator Auxin. Some of the main effects of this particular PGR include promoting the growth of stems, promoting fruit set and development, and inhibiting the effects of ethene.
The latter is the gaseous PGR that promotes fruit ripening and abscission (fruit and leaf drop). With ethene no longer inhibited, the gas is free to build up in the tomato fruits, causing them to change colour and sweeten. And as these plants have set all the fruit they’re likely to for this year, and in some cases the fruits are already bigger than they strictly need to be (see below) then that’s the result we’re looking for.
In the process of trimming back I checked the fruit and discovered that all was not well. For starters, a couple of trusses on one of the Bulrush-grown plants were showing clear signs of the dreaded blossom end rot:
As that linked-to disorder profile from the British Tomato Growers Association (who should know a thing or two about toms) explains, it’s not caused by a fungal infection, rather a shortage of the essential mineral calcium. The shortage isn’t necessarily due to a lack of calcium in the growing medium, but is more than likely due to a lack of available moisture to carry the dissolved mineral up into the plant.
In this particular instance I can rule out one other potential cause – a high-nitrogen feed – as the only feed I’ve given the plants has been 50% higher in potassium than nitrogen (although apparently potassium, in turn, can interfere with the take-up of calcium, so maybe the feed played a part). But as I noted in my last update that the peat-based compost seemed to be retaining and holding less water than the peat-free, then I think we can point the finger in that direction. Obviously I have to take my share of the responsibility for not irrigating quite frequently enough, but in my defence I’ve been watering all the plants equally (and trying to avoid either waterlogging the growing medium or causing the fruit to split due to over-watering) and there’s no sign of blossom-end rot on the plants in the peat-free growbags.
Not that the peat-free plants have been completely without problems of their own though. As you can see from this pic, the plants grown in the SylvaGrow bags have shown clear and classic signs of interveinal chlorosis caused by magnesium deficiency:
According to my RHS L3 textbook, magnesium is a common enough element and deficiencies are usually only found in intensively cropped sandy soils or chalky, or over-limed soils. I could have addressed the issue with dilute epsom salts, but as this sort of disorder usually appears in the older leaves first, and those were the ones I removed (as mentioned above), I’ve decided to let it lie for now rather than dose all four plants, possibly unnecessarily.
There was one other problem with both of the peat-free plants, which didn’t manifest until a couple of days after I’d trimmed everything back. This time it was a case of the plants being too successful at setting fruit for their own good. A whole truss of fruits had fallen off of each one, the weight of the fruits presumably being too much for the stem/truss joint to support.
This is rather unfortunate, as it obviously affects the overall comparison of fruit yield and quality, but can’t be helped. I’ve recorded the weight of the fallen fruit and have put them in a bowl on a sunny windowsill, with an over-ripe banana, to see if a bit of extra ethene will help them towards ripening. Otherwise, that’s one batch of green tomato chutney already planned.
Hopefully in the next few weeks I’ll see a few fruits ripening up (preferably still on the plants) and will be able to start taste-testing and saving the seed to go back to the Heritage Seed Library. I’ll keep you posted.
How about you? Having a good year for tomatoes, or are yours late / unripe / diseased or disordered? Please do let me know, via the comments.