I think I'm still officially a noob, so I'm going to ask a noob question: I have some green cuttings in my humidity bin. They have been doing well. Ample roots and lots of fresh green leaves popping out. Today I noticed that a couple of the new shoots with have a little bit of browning on the tips. What's the problem?

The humidity box temperature is usually around 80F during the day and drops down to around 70F at night. I have a heat mat under the bin set for 80F.  I also use LED lights from sunset to about 10PM to extend the "daylight" hours. Humidity in the bin is usually at 99%, but I open it several times a day, and then the humidity drop down to room level and starts uilding back up after I recover. The cups are filled with 40/60 chopped sphagnum (left over from rooting) and Perlite. The cups weighed 4.5 oz dry and about 5.25 oz after I watered them. They weight has not changed significantly since I put them in cups about a week ago.

So, before things go too far, what causes the tips of new green shoots to turn brown. It's happened to two of my plants and I would like to prevent it from becoming a major problem.

Thank you in advance.

Hi Paul, 
Based on my experience you appear to be doing many of the right things. Sometimes the new leafy growth will decay, maybe due to the high humidity environment of the enclosure.
Do not dismay! the roots are the most important part at this stage. Persevere and let the roots grow. The leafy growth will in my experience come back. If there is a lot of roots see "Rich's Propagation Method" then please go to the next step of removing them from the humidity chamber.

Paul,
it has happened to me too few times, I pinch right bellow the brown tip and if they have roots (even like...1cm) move them and pot them in a regular fig mixture soil that you formulate. No need to wait any longer. Longer you wait more of the brown tips you will notice. Those are rot due to too much moisture and not enough light or sunlight with fresh air.
After you plant them you can still use a cover but make sure it's just to protect them from winds and other outdoor elements. I use (one or two) hole drilled  individual sea through covers. That keeps the air inside gentle and just enough moist so the tender new growth won't dry out.

Edit: move them, not remove them.

Thank you Rich and Aaron for your responses. Rich, glad to hear that a little damage to the greenery is not necessarily a death sentence. If too much humidity can cause browning, then I think that must be my prob. Can't get any more humid than I have it unless it's raining. Anyone know what the ideal humidity should be? I think rather than removing them from the bin, maybe I could just dial down the humidity.

Aaron, when I say they have nice ample roots, I just mean for having just come out of the moss. There were lot's of dense roots completely covering the bases of the cuttings, growing straight out in every direction like little root fros, but they were still only an inch long. I thought most people keep them in cups until the roots show through the sides, and I'm not there yet. Also, I think they are getting plenty of light, The bin is sitting in a north facing window getting lots of indirect light, plus I give them about 4 more hours of grow lights after sunset.

I should probably also change my cup mix. I've used straight Perlite in the past, but found that it gets too dry too easily if I neglect them a little bit. I though mixing in the moss would balance out the mix. However, when I prepare moss for rooting, I steam it in a tamale pot, chop it into small particles in the Vita-Mix, and then I wring out every last drop of water before putting the cuttings in it. In my cups, I mixed the damp moss with dry Perlite. But then I added an ounce of water to each cup. That's not that much water, but I wonder if the mos grabbed every drop of it and is making wet spots. Promix sounds good, since that's what I'll use in the big pots anyway.

Last thing that I have to say is that Rich's Propagation Method looks like it produces ridiculously beautiful trees. I will have to try it.

Yep too much moisture in the air. Maybe crack the lid an inch or two all the time, let the leaves on the cuttings tell you when too much fresh air is getting in. You haven't said how long the cuttings have been in the chamber, but you definitely want to take the top off and air them out once or twice a day. Use some sort of timer and gradually increase the time the cover is off. It is a good idea to have a fan running in the room also to make a ambient breeze, not blasting directly on them but just enough to circulate the moisture saturated air out of the tub and replace with fresh dry air. As soon as the leaves start to droop you need to turn the fan off and replace the cover(completely closed to build up humidity quickly), this light stressing will stimulate the cuttings to grow the roots faster and harden off to dry air faster. You build up time daily starting at like 10 minutes and increase a minute or two a day; but always letting the leaves tell you when to cover. If the leaves droop it's OK, if they loose too much turgor pressure and start to wrinkle you need to cover them and get the humidity up fast. As the cuttings start getting used to the dry air the time increments will increase more as well.

Here is my cup mix after I have initiated rooting in a bag.

2 measures perlite
1 measure Jiffy seed starter mix or peat moss ( hydrated coco coir could probably be used here as well but I haven't tried it yet)
0.5 measure vermiculite

Usually, on about half the cups per variety I start I will do something slightly different. I fill an empty cup that I will be using for a cutting about 1/4 to 1/3 full with the potting medium mix I use for my big trees and then top if off till nearly full with above 2:1:0.5 mix. Then put an empty cup inverted on top like a cocktail mixer and shake to mix. I do this to add a bit more nutrients to the otherwise nutrient barren 2:1:0.5    I still always do some cups without the added soil though, because on occasion I have had cups with soil in mix experience sudden death syndrome when they were growing nicely with a fair amount of roots recently hitting the cup. But a greater percentage of the time they grow faster and stronger than those without.

Calvin, they have been in the bin about a week. The leaves aren't even big enough to droop yet. Some of them are those teeny, tiny ones, and others are a little bigger and getting ready to unfold.It's the tips of some of the ones getting ready to unfold that have turned brown.

Rich, sounds like I need a fresh batch of Perlite. My current mix was not measured. I just used the bottom of the bag of Perlite that was sitting in the shed, which wasn't quite enough to fill the cups. So, I bulked it up with my leftover rooting moss. I have added a little moss to my cup mix before, but I think this time I added a more than a little.

oh gosh no...you don't remove roots. I guess it was a poorly organized sentence. I'll edit it.

What I want to say is that, as soon as you se little roots just replant them in a regular fig soil and keep under cover for a week or so, then remove the cover slowly.

OK.  I think he had already cupped them up if I'm not mistaken. 

Quick update: On Friday evening, I made a small gap in the tent (using a dry cleaning bag for a humidity tent) and since then the humidity has been staying around 80%. I bought some fresh, fine particle Perlite yesterday and I was just about to re-cu them in Perlite with a sparse amount of Pro-Mix. However, I see that brown tips now have the beginnings of fresh green emerging from just behind the brown area. I think that my current cup mix is not necessarily ideal, but I don't think that was the cause of the browning. I think it was just too much humidity. Not sure if it is worth disturbing the roots to change the cup mix, or if I should just leave them alone and be extra careful about not over watering the cups (if I need to water them at all).

Thanks again for all the support. Sometimes, seeing a few tips turn brown is the beginning of a disaster, but it looks like things are moving in the right direction.

PS: I took a few cuttings from a wild fig tree yesterday, so I will be starting some new rooting experiments next week, including Rich's method and the one node direct in Pro-Mix method.