Sweet Pea plants growing on a willow garden screen

Air-pruning plant pot experiment – UPDATE

Growing plants in air-pruning plant pots was a new experience for me this year so I have been watching and learning from my Sweet Peas as they have gradually progressed.

My air-pruning experiment: the project progress

My six upcycled air-pruning plant pots now complete with their newly sown Sweet Pea seeds
My six upcycled air-pruning plant pots now complete with their newly sown Sweet Pea seeds

It seems a long time since mid-April when I sowed the Sweet Pea seeds in their cosy grow bags inside my upcycled milk carton air-pruning plant pots. The seeds quickly germinated and the Sweet Pea plants were soon on their way.

Air-pruning plant pots firmly secured to the gate and the Sweet Pea plants arranged on the jute and willow garden screen
Air-pruning plant pots firmly secured to the gate and the Sweet Pea plants arranged on the jute and willow garden screen

When I put them outside in the middle of May, the plants only just reached up far enough out of their pots for me to encourage the shoots to set off on their journey up the jute and willow garden screen that I had specially constructed for this purpose.

By the end of July the plants were grown to their full height (1.8 metres/6 feet) and the first flowers appeared … pink, followed by white and then a deep maroon.

Pink, White, Maroon - Sweet Peas on the willow screen
Pink, White, Maroon – Sweet Peas flowering on the willow garden screen

My air-pruning experience: thoughts and observations

Whilst generally I am very pleased with my air-pruning experience during this Spring and Summer, I have encountered a couple of problems with my gardening experiment that I thought I’d talk a bit about in this post.

Air-pruning plant pots in the microclimate behind the wall
My air-pruning plant pots in the cooler, damper micro-climate behind the wall

I set three pots of plants to grow from behind my small yard wall (approx. 90cm/3 feet high) and three pots of plants to grow up over my yard gate, which is around the same height. Although these two areas are only inches apart, they have very different micro-climates.

The small area behind the brick wall is fairly dark and damp because it is immediately adjacent to our refuse and recycling bins. I had also previously planted my new Willow cuttings in their pots in this corner of the yard and, as they had grown on a little, they affected the light level too. The combination of these elements means this part of the yard tends to stay cooler with no direct sun.

As I'd anticipated the Sweet Pea plants are mainly growing on the outside of my backyard garden screen
As I’d anticipated the Sweet Pea plants are mainly growing on the outside of my backyard garden screen

The wooden planked gate forms the boundary to the other half of the yard. With the open yard area immediately inside the gate, this half of the yard has more air movement, plus the warmth of the sun soon warms up the wooden gate.

In the cooler, damper conditions behind the wall, it wasn’t long before the snails showed up! When I say ‘showed up’, it was mainly a case of ‘left a trail’ … not only of glistening slime, but also of half-chewed leaves – though only on one particular Sweet Pea plant. Why only one plant, I can’t be certain – but I was pleased to see at least it wasn’t all three!

Snail in Sweet Pea grow bag
Spot the snail snuggled into the Sweet Pea grow bag!

One day I managed to catch up with my plant-munching visitor as it snuggled down into the evidently-too-cosy grow bag! Have you ever found yourself addressing a mollusc?! I must say, I took pity on the poor starving creature who was, of course, merely seeking an evening meal and a bed for the night! I did however remove it from the Sweet Pea pot and found it a new home elsewhere!

Moody mollusc - my snail visitor
Moody Mollusc peering disgruntledly from under its shell

There was one other aspect of my Sweet Pea air-pruning plant pot experiment that I have could have been happier with and that relates to the size of the pots I chose to use. If you have grown Sweet Peas before, you will know they normally prefer to grow in quite deep soil. However, I had previously grown them successfully in a pot that was not much deeper than the air-pruning plant pots I was using this year, so that was why I had decided it was worth the experiment.

The problem I encountered was this: as the plants grew taller, the lower leaves quickly yellowed, despite regular watering and feeding. I took a close look at the root systems as far as I could observe them from the outside of the pots. The roots had grown well and exactly as expected in the air-pruning plant pots. There were only the tips of roots showing inside the closed-in areas of the pots. Where the fabric grow-bag was open to the air, the roots had not penetrated the grow-bag. I will be taking an even closer look at how the root systems have developed when the plants are finished flowering and I take them down.

Visible root growth in air pruning plant pot
Root growth in one of the air-pruning plant pots on the wooden gate
Roots in air pruning plant pots
Roots in the air pruning plant pots behind the wall

The plants have reached their full height and flowered, but the yellowing of the leaves has somewhat spoiled their overall appearance on the willow screen. I definitely feel the Sweet Pea plants needed larger pots with a greater quantity of compost to supply them with sufficient nutrients and water. (Apologies for the slightly blurred image below – we had windy weather in August and it was impossible to find a time when the light and the weather allowed for better photo shooting!)

Yellowing foliage on my Sweet Peas
My Sweet Peas at the end of August – flowers but also yellowing foliage

I was very pleased that the Sweet Pea plants grew to their full height, though on hindsight, given the plant pot size I had used, I would probably have been better managing the growth differently. I nipped out the main growing tips when the plants reached the top of the screen, but if I had done this a little earlier and kept the plants a little shorter, I think perhaps the issue with the dying foliage may not have been so bad.

The size of the pots has definitely been an issue I’d rethink for another time. I need either larger pots for Sweet Peas or perhaps I need to choose a smaller growing plant. Another idea I had intended for some of the Sweet Pea plants was to plant them into a wooden plant trough. But, as so often happens, time simply ran out for that idea this year. However, I may contemplate creating some troughs in either wood or woven willow for next year so I shall add it to my Winter projects list!

J Peggy Taylor

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