Hi, what you may consider is that the smaller PEG (it can go down to 3500 Da) may get absorbed by the plant. What could you try is to label it with some fluorescence dye or something (radioactive label or whatever) and check, whether it penetrates your plant.

PEG4000 is much more likely than PEG8000 to be absorbed by the plant. Also, remember that for PEG osmotic potential is not directly proportional to the solute concentration. Also osmotic potential does not change linearly with PEG size so you may need to change your calculations from PEG6000.

Hello,

These questions were largely answered over 50 years ago! See this publication

Free Access

ABSORPTION OF POLYETHYLENE GLYCOLS BY PLANTS AND THEIR EFFECTS ON PLANT GROWTH

D. W. LAWLOR

First published: April 1970

https://doi.org/10.1111/j.1469-8137.1970.tb02446.x

Look at Lawlor D W on ResearchGate where it is available or

on the New Phytologist (Wiley) website where a PDF is given.

Hope this helps.

David W Lawlor