Reasons for nitrogen deficiency in mid-flower?

[Landracey]

We know what nitrogen deficiency looks like. We also know that nitrogen deficiency in late flower is no biggie. But what about nitrogen deficiencies that spread up the plant at week 5/6 for hybrids and early finishing sativas, i.e plants that have about a month to go. Should more be added to a pure soil mix, or wouldn't it make a difference now?

The plants vegged outdoors for three months so are fully mature. I am finishing them under 600w HPS (Phillips) indoors because I'm growing at 51 degrees north. They are in 40 gallon potato sacks.

I planted them into these sacks in month 1 of veg. Maybe I should have given them bigger sacks, but that wasn't possible for several reasons. What I'm thinking is that the nutrient deficiency (nitrogen) could also be to do with compacted soil in these sacks, and rootballing, but I'd like to canvass opinion from seasoned growers here. Thanks.

 

[BigBudsBunny]

looks normal to me - fan leaves die off as the end is near and the plant uses whatever is in them. if they reach mid flower with some deficiency - they are usually going to make it the end no matter how ugly they get,, but the yellowing of fan leaves starting mid flower seems normal to me - there should not be a rapid yellowing of all leaves at the same time tho.

 

[SmokingWings]

But what about nitrogen deficiencies that spread up the plant at week 5/6 for hybrids and early finishing sativas, i.e plants that have about a month to go. Should more be added to a pure soil mix, or wouldn't it make a difference now?

Adding more nitrogen to the fertilizing schedule does not seem to do enough once the leaves are turning yellow during the flowering cycyle. I often see it as a case of once the plant starts to take the N from the leaves it will continue to do so even if extra nitrogen becomes available to the roots.

Over the years there have been growers wanting help because their fan leaves have started to turn yellow at this stage of growing. They write that it started around the 2nd week to 4th week after the 12/12 hour light schedule started for a photo-period or the start of flowering with an auto-flower plant. They would be asked what fertilizers they were using and the doses. More times than not the answers were that they either stopped fertilizing period or dropped the doses to 1/2 or less of the recommended amounts.

Gotta get the nitrogen levels back up before the plants start to cannibalize their own leaves. Waiting till the fan leaves start to show the deficiency is too late.

 

[StarkRaven]

It's normal when your plant is switching from veg to pre flower just add some cal mag and nitrogen the cal mag will help prevent nutrient lock out and help deliver more nitrogen to your plants. It will also strengthen the branches so do any low stress training now before your branches get woody.

 

[SmokingWings]

Adding more nitrogen to the fertilizing schedule does not seem to do enough once the leaves are turning yellow during the flowering cycyle. I often see it as a case of once the plant starts to take the N from the leaves it will continue to do so even if extra nitrogen becomes available to the roots.

Though, adding a nitrogen source even after the yellowing starts might be enough to slow down the yellowing for the next week or two. I have found several fish fertilizers with a mild dose of nitrogen, usually 1 to 5 percent and will use that mixed into the water for one session a week or every two weeks. With numbers like that is it a mild enough dose that it will not cause an excessive N or nitrogen toxicity condition.