I think it has to do with satisfying the dormancy period for the plant and getting them inside before temperatures get too cold. So it probably does make some difference to what zone you are in. Someone please correct me if I'm wrong.

This link has some info on grafting.

Sc77 why do you air out the chamber? Also, prior To grafting are you still turning the lights on for 12-14 hours a day?

too much humidity can lead to mold.. mildews and algae .... inside a plastic bag ... so .. once in a while.. you freshen the air.. and let the greenery dry a bit .... or im wrong ...

to many garden newbs.. fixate on the calendar ... the key above is not such ... but rather the hours of chill ... and if those hours cause you to do otherwise from the julian calendar.. so be it ... all hail ceasar ... lol ...

i dont recall how many you are talking about ... but there is my usual thought.. bring them in .. in waves ... dont make the whole process dependent on one guess ...

ken

Yep, pretty much the reasons Ken mentioned. Introduce fresh air, sometimes to cool off the chamber, and occasionally wipe down the ceiling if water droplets are building up. I always did this without any negative impact to grafts, later I learned your supposed to keep it sealed the whole 2 weeks post graft...but, I dunno where that came from. If you just open it for 1 min or less and close it back up, the humidity will get back up pretty quick, so no real risk of drying out. I just wouldn't keep it open for long during those two weeks

I just have cuttings in my chamber now, while I try to get it ready for grafts. I’m having a hard time keeping droplets off the ceiling when the light is off. When the light is on the droplets on the ceiling disappear. Is the concern with them that they will fall on the plants and cause problems?

I have a pond fogger in my chamber. When I open the chamber the humidity might drop to 75%, but once I close it and turn the fogger on it’s back up to 95% in just a couple of minutes.

Yes, It's no concern if droplets fall on cuttings, but if a drip of water gets into the graft union before it heals, it will ruin the connection. You might need to put your fogger on a timer. Mine isn't too powerful, plus my chamber is taller, so i usually don't get water droplets on the ceiling until it's closed for a few days

Yeah, I basically keep it off all the time. It seems to stay plenty humid without it, but if the humidity does drop it works great for a quick rebound.

A friend of mine who did a lot of professional grafting here in the PacNW used to have his understock in coldframes. (unheated greenhouse) When the understock buds began to swell he would go outside and collect the dormant scions and graft them to the awakening understock. That way, the scions wouldn't draw more moisture through the fresh grafts than it could handle. The graft would be well on it's way before the scion woke up. He did mostly Japanese maples, but the principle still applies.

Something I’m noticing with my chamber is that my humidity reads much lower when the light is on. While off I’m getting 99%, but when the light is on it will drop to 70% if I don’t turn on the fogger. Even with the fogger running I’m only getting up to 80%.

I dont understand the reasons for that. Could it be my humdity monitor is misreading from the light shining on it? or is the light actually causing the humidity to drop? The reason I kinda doubt the humidity is actually dropping that much is the fact that there’s water droplets all over the walls and some on the ceiling.

Also, as expected the light does warm the chamber up. It never gets to 75 F but I have seen it reach 73 F and it seems to stay right around 70 F for the most part whenever the light is on, which is about 10 degrees more than what it does while off. I hear 45-75 is okay for grafts, but if I’m sitting on the higher end of the range a lot of the time is that going to cause problems?

If your hygrometer measures relative humidity, that would explain why the humidity varies with variation in temperature. Warmer air can hold more moisture that cooler air, so the same humidity will read lower at a higher temperature because it's a percentage of the total amount air can hold at a given temperature.

A thermal hygrometer, will measure absolute humidity no matter what the temperature is.

I can't help you with your other question about ideal graft temperatures.

When we talk about humidity for grafts are we talking about relative or absolute?

I think we're talking about 'high' humidity.

Find out ideal temperature for your grafts to knit, keep it at that, then monitor humidity for what sc77 recommended.

No need to overthink it, just high humidity. I have a cheap digital gauge which usually reads 90% plus, but Its probably not that accurate anyways. If you have water droplets forming on the walls of the chamber, you are good. That is plenty humid. If they start forming on the ceiling, you need to actually lower it by turning off humidity source or airing it out and wiping down the ceiling.

As far as temp, 50-65 is probably ideal. If the temp goes above 75 that is not good, and you will start impacting your % success rate if you don't cool it down fast.

Hey Jacob, the warmer the air, the more moisture it can hold. Once it is fully saturated with as much moisture as possible (100% RH), that's when droplets will bead out on the walls an ceiling. If it is less than fully saturated, your RH-meter will compare the amount of moisture in the air to the total possible at whatever temperature you're expressed as a % - that's your RH. So when the temperature climbs, your RH will drop since the total the air could hold goes up.

But, this is not just a geeky aspect of the math - it has real consequences. Since 100% RH is the most the air will hold, your graft union cannot dry out b/c the air will not accept any more moisture. If the temp goes up, causing the RH to drop b/c the air can now hold more moisture, let's say it goes down to 70%. It has the same amount of moisture in it but now the air isn't saturated and could hold more moisture, and it becomes possible for moisture to evaporate out of the graft union and into the air.

You're safest using a graft sealant like Doc Farwell's and then it becomes less critical to completely control RH as temperature changes.

I came across this for $6.50 at an overstock discount store of all places. Anyone familiar with it? Will it be okay for conifer grafts? I have parafilm tape already so I guess I could use this to seal the top of the union?

So I decided to bring some rootstock in today hoping to graft by around the first of the year. Some of the understock I have I purchased from Western Evergreen and I think that the Virginia weather may have caused them to wake up a little early. I had them heeled in with mulch and when I lifted them out most of them had nice healthy white roots already. Should I go ahead and try to graft on those in the next few days? What do you all suggest?

Nope, too soon. Wait until 1/4th of the understock are breaking bud. I think it's better to wait longer than to jump the gun on the first sign that a plant is waking up (i.e. white root tips). I did that one year and believe they were not pushing enough energy yet to support the scion and I had more failures than usual.