Looks to me like you bleached the plant tops by having them in too much sun. The sun can turn the leaves yellow and then white. I even experienced a little under my LED light in my last grow so I had to raise the light. I'm 95% that they got bleached. Those white bleached leaves are beyond repair but the yellow leaves may survive however they won't do much for the plant. They will always stay yellow. Only the new growth will become green again so let's hope your plants tops aren't too damaged. If my cool running LED can bleach a plant then you can be sure the sun can, especially if it was used to being a house plant and then put out in the sun, even under a cloth. Keep the plants in the shade from now on. the reflected sun from the foot path etc will be enough to promote growth.

Sure the cloth might take some of the heat but when the weeds are started indoors and then brought outdoors, when the sun is baking, you need to keep them in the shade and only put them in the sun for 15 minutes every couple of hours. You then build up the plants resistance to the new conditions. Going from indoors to outdoors is like one of us being placed in a desert without suntan lotion

So I would think it's a bleaching and the cloth you used saved them from massive heat stress. The edges of the leaves would begin to brown if it was heat stress.

This is not a nute burn or a deficiency. Nute burns don't turn the top white not does a deficiency. An Zinc, Iron or nitrogen deficiency can yellow the leaves but not make then white.
A PH problem will show brown blotches on the leaves and will turn the leaves eventually brown, not white.
silent leprechaun Reviewed by silent leprechaun on . Plant problems with all 4 of my females - Please Help ! Plants were germed in rockwool and were working out fine and then I potted them into a mix of perlite, peat moss and good quality potting mix. About a 2 weeks in under the shade cloth down the side of the house and they are starting to turn all really light green on the top node and the lower leaves are starting to fold over. I did have them on a 1/3 strength mix of canna vega a+b with a ph of about 6.6. Also one of my northern lights is looking a bit weird. It is growing very nicely Rating: 5