Question for the great ones whose knowledge far exceed mine

Last year I had several decidious trees not turn to changing leaf color and only when the frost came and killed the leaf did they turn brown. They then held their dead leaves most of the early winter. Why did they remain green, not change color and drop their leaves?
Acer saccharum
Parrotia 'Vanessa'
Acer Glabrum
Cornus Alterfolia 'Joyous Summer'
I wonder if I need to stop irrigating to let them get stressed? I have matching specimens that did what was expected of them. It seems the ones in the sun and were growing well were the ones that did this. Except the Cornus. They all have been here for several years except the Parrotia.

This past fall we had excellent fall colour. I think it had to do with less rain and better weather. Cutting back on watering around late August would probably harden them off better and maybe better colour. I'm just guessing.

That is my thoughts because I forgot to turn off the irrigators in September. October had a good frost and followed with rain intermittently. I think I need to stress the plants with a threat that I will take them out of the sun of Montana and move them to BC. LOL

Give it a try. Stressing would probably give you the colour better. They might have been grown too soft with the extra irrigation.

Answer from VV: I just got home from driving through (for us) a pretty good snowstorm. 4" on the ground, and up to 10" in the forecast for Louisville/Lexington axis. I think I'm staying home tomorrow.

After reading your link, I agree with your supposition of too much care too late into the fall.

It isn't stress, per se; that's applying a human quality to plants. It is creating an abnormal condition that your plants are all too eager to take advantage of. As growin and you both noted, watering above and beyond what the plants should normally experience caused the plants to continue growing into the period during which they should "harden off" and prepare for dormancy.

Preparing for dormancy includes using up the chlorophyll in the leaves (the green stuff), which then reveals the "hidden" colors that were there all along - yellows, reds, oranges, and purples. It also triggers the hormones or proteins that cause abscission, or leaf drop.

By not going into dormancy normally, the green leaves were caught on the tree and killed by low temps, and thus no fall color and no drop.

I'll post this on the thread, if you like.

You might also have "micro climates" on your property. I have trees planted on the top of the hill on my property that turn color but the same species down in the hollow by the creek stay green longer and have yet to give me a good fall show of color.

I have certainly seen a moisture link over the years. Like growin, this past year was a banner year for color around here. But that seems pretty drastic. Were you irrigating that much? Also, there are other factors too - changing length of day / night and temperature. What a bummer to miss the big show.

victorgardener - I noticed the day/night temps were sharper/crisper so you might have something with that too.

Well that's the belief - sunny warm fall days followed by cool crisp (but not freezing) nights result in best colors. Supposedly the warm days trigger more sugar production by the leaf but the cool nights prevent the sugars from leaving the veins. This is the recipe for strong anthocyanin pigment production.

I had some sugar maples near by but on different irrigation systems do fine but one that was in the sun with a spray irrigator didn't. One parrotia in more shade did good but the sunny one didn't. We had our usuall perfect October with cold nights in the 30s. Followed by sunny warm 50 and 60sF afternoons. You are right about microclimes but I have planted based on those variances. We irrigate all late summer to overcome the dry airs we have in Aug and Sept. The plants seem to enjoy the irrigation. The trees that were planted in our lawn did fine (mature specimens) that only had once a week irrigation 1 to 2 " soakings. Thank for the ideas.
This is one acer sacc. that had good color and leaf shed. I have about 9 sugar maples and only one did the no color change.

This is the one who didn't. You can see it to the left and back. Below it is the burning bushes and they colored up fine.

This is the burning bush underneath.

You can see the other trees in the yard did fine.

Well that does sound like it's the only difference alright. Great shots, Steve. Wonderful landscape.