One way to clear weeds using no-dig methods is to lay down black polythene over a thick layer of mulch and then grow squashes/pumpkins through it. This seemed like a great plan to me earlier in the spring, so I got some weed suppressing black mesh and laid it over the top of a very weedy patch (docks, nettles, brambles, butterbur and more) that I wanted to clear for next year and planted several squashes and courgettes through it. What I didn’t do was add the mulch first. A mistake.
What I am finding is that many of the plants are developing yellow leaves in varying degrees (I think that there are 12 plants in total, and at least 5 or 6 of them are suffering). Some plants have a very bright, almost luminous, yellow dappling on the leaves, others are just pale yellow all over and others are yellowing at the edge. I dot know exactly what the different problems are, but from what I have read, nearly all the causes of any yellowing leaves in cucurbits comes down to more or less the same thing – a lack of nutrients (iron, magnesium etc) or a lack of water.
This is why I think it was a mistake not to have mulched. I’m not sure that the soil was particularly good quality – it was quite heavy, cloggy and clay-like – and since it has been so dry for weeks now it has been difficult to make sure that the plants are getting enough water through the mesh (it’s surprisingly difficult to water squash plants through the mesh as it’s on a slope and the water just runs down and away, so I have to carefully aim the watering can into the hole in the mesh.) Had I mulched first, the plants would have had that much more access to water and nutrients and I think this would have prevented a lot of the leafy problems that they’re experiencing.