On watering, comfrey feeds, cabbage white butterflies and a caterpillar that’s munching my tomatoes.
I hope you and your gardens are coping with the heat. We have recorded 28-30C in the garden, with a maximum of 31.3C yesterday.
I have been watering conservatively. All my larger pots get watered daily and I have placed all the smaller pots on trays so the water doesn’t drain away. I am a bit meaner with my raised veg beds, giving them a drench every few days. The thinking behind this is to make sure the water penetrates deep into the soil to the roots. If you water little and often, you encourage superficial roots which are more prone to water stress. And I have added some fresh mulch around new transplants.
I have also put out several shallow trays of water for wildlife at different points around the garden.
My water butts have run dry, but there is plenty in the dipping pond and in my three one-cubic-metre IBC storage tanks.
However, the end of the heat wave seems to be in sight, and we’ll probably get a few torrential downpours.
Comfrey
One of my most versatile plants in the garden has to be comfrey. Its flowers are much loved by pollinators, it makes a great liquid feed for my crops and it can also be used as a soil improver. Not surprisingly, I have grown this plant for decades – buying stocks of Bocking 4 and 14 for my garden, which have been propagated and moved with me ever since.
As a member of Garden Organic, I soon learnt about the benefit of this plant which led me to reading the books of Lawrence Hills, who wrote at length about Russian comfrey. He was one of the founders of the Henry Doubleday Research Association (HRDA), which is now better known as Garden Organic.
If you look in gardening books, it’s suggested that comfrey liquid feed is high in potash, so good for tomatoes while nettle liquid is high in nitrogen and better for hungry, leafy crops. These claims are based on the work of Lawrence Hills. But at the time, it was expensive to test samples for nutrient composition so the range of samples that he tested was limited. His results showed his comfrey feed to have a potash content that was similar to typical tomato feeds that you can buy today.
Nowadays, testing is much more accessible, so back in 2022, Garden Organic setup a members’ trial to revisit these claims, and test comfrey and nettle liquid feeds made from a wide range of sites and I was delighted to read about the results in the latest edition of Garden Organic’s The Organic Way.
At each site, participants grew comfrey and nettles under similar conditions, took a cut from each in May, brewed the feeds until the end of July and then sent a sample of each for NPK testing at the Centre for Agroecology, Water, and Resilience at Coventry University. These results were compared with values from commercial products.
The results showed that comfrey fertiliser had more K (potash) than nettles, but nettles had significantly more N and P than comfrey. The overall mean values for NPK (mg/l) were:
Comfrey N 97 / P 40 / K 551
Nettles N 153 / P 55 / K 507
However, there was quite a lot of variability in the results, for example comfrey had an average of 551 mg/l of K, with 50% of the results falling within the range of 426-707.
It was interesting to note that Hills’ own results had an average K of 340 mg/l compared with 293 mg/l obtained with a typical commercial feed. His figure of 340 mg/l was quite low compared with the members’ results, so does that mean different soil (clay has more K than sandy soils), better extraction, modern analysis or does it relate to the variety of Bocking comfrey being used? Today, we grow mostly Bocking 14, but may be Hills’ used leaves from a mix of his Bocking varieties to make his liquid feed? I don’t know, but I think I’ll be rereading some of his books.
Garden Organic has put together some recommendations based on these trial results. Interestingly they stated that the liquid fertiliser samples had K levels similar to commercial feeds that had been diluted and ready to use, so there was no need to dilute the comfrey feed further. I have always diluted the stinking liquid from my bucket so now I won’t bother.
Also of interest, was the fact that nettle wasn’t that different from comfrey with regard to K levels, so we could use nettle feeds on our tomato plants. In the past, I have popped nettle leaves into their own bucket of water but it may mean that I don’t have separate? What do you think?
Using comfrey feed as a foliar spray
I have used a diluted and strained comfrey feed as a foliar spray on my plants. The crops I tend to target are squashes and courgettes as it is supposed to reduce the incidence of powdery mildew. Its also thought to be a tonic for plants that are stressed, so I have been spraying it on my tomato plants in the greenhouse.
How do butterflies find their target plants
Another idea occurred to me as I watched a number of cabbage white butterflies dance around the garden. Butterflies might be experiencing one of their worst years, but numbers of cabbage white butterflies seem to be undiminished. My brassicas in the veg beds are mostly covered with butterfly netting, but I have planted quite a few in the flower beds.
Butterflies use their senses to find their host plants, but the one that matters the most initially is smell. Each type of plant emits a signature scent that’s formed from a particular mix of volatile organic compounds or VOCs. Butterflies have an excellent sense of smell and they can detect these VOCs from some distance. Once they have located the plant, they use their sense of taste to check of the quality of the leaf for their eggs. Amazingly, they can actually determine through taste, if the plant leaf contains enough of the right nutrients to support their caterpillars.
So how can I confuse the butterflies? I usually hope that by planting the brassicas individually in the flower beds, their scent is masked by the VOCs emitted by the plants around them. But what if I gave them a foliar feed of comfrey? Would this confuse the butterflies? I am giving this a go as I have nothing to lose. The foliar feed will benefit the plants any way and hopefully the smell may be enough to confuse the female butterflies. Meanwhile I will do my usual check for clusters of butterfly eggs.
Moth eaten tomatoes
Some of my tomato plants having been looking moth-eaten! A bit of investigation revealed a number of green caterpillars. They looked like moth caterpillars, but not being an expert in their identification, I posted a photo on my IG stories and soon after I received a positive id. So thank you Jill (@corvedale365) who identified it as a bright line brown eye moth caterpillar. They eat a range of plants including nettles, so she wasn’t sure why they are munching my tomatoes! They can burrow into ripening fruits so I need to check on this.
So on this note,
Happy Gardening
Sally
Talks
Talk 13 September Talk by Sally at Yeo Valley Gardens, Organic September Celebrations, nr Bristol - you can book a ticket via the Yeo Valley website
Talk 21 September Sally is speaking to the Somerset Hardy Perennial Society, West Monkton, nr Taunton
Sally and Kim give talks on a wide range of topics. Please get in touch if you would like to arrange a talk or webinar. You can also arrange group visits to Sally’s experimental garden.
Really interesting and useful about the nettle and comfrey feed. It would simplify our work collecting them and making the liquid if they just went together in one container