Autumn Colour Failure

For the last three autumns, all my trees that were bought for their autumn colour failed to produce any colour. Trees planted summer 2021 through to March 2022.

2x Liquidamber 'Slender Silhouette' (Gum Tree)
1x Acer Freemanii 'Morgan'
1x Prunus 'Amanogawa' (Pillar Cherry)
1x Sorbus 'Joseph Rock' (Yellow Berried Rowan Tree)
1x acer shirasawanum 'Autumn Moon Maple'

In the autumn of 2023 i discussed the issue with three different nurserymen at two different arboretums. All advised that i should treat the ground around each tree with sulphate of iron every month for a year, then perhaps twice a year thereafter. I have done this every month starting October 2023.

Spring 2024 and these same trees are now unfolding their new leaves and there is a very noticeable difference that's striking me already. Rather than starting pale green / yellow before turning darker shades of green, the leaves are unfolding red and a dark orange and some are starting to turn a pale green / yellow colour around the edges. The new growth and the trees as a whole are looking better than ever, fighting fit.

I hope the leaves start to turn a darker shade of green for the summer before turning red in the autumn given plenty of sunlight, little or no rain and cooler temperatures but not freezing.

Some GW refugees may recognise this thread, and i thought i would restart that discussion here. I do plan on updating this thread during the rest of the year.

 

Welcome here,
An interesting thread. While you don't seek advice, it would be of general interest if you felt able to give your (approximate) location, such as first part of postcode if Uk, county or city. We promise not to call to view your trees!; although photos are welcome.

 

Thank you infradig,

A discussion was thrashed out when i sought advice on the GW forum in the autumn of 2023. Just wanted to share my journey with those that contributed then and those on this GC forum moving forward now.

 

Update June 2024.

Trees that are being treated monthly with Sulphate of iron are growing differently this year. i know it's been dark, cool and wet but comparing trees like for like with untreated trees they are different.

Leafs are smaller with a darker colour and a lot more of them. Like for like, untreated trees have larger, paler leafs and fewer of them.

The Autumn Moon Maple and the Paper Bark Maple leafs are sporting leafs with an orange tint to them around the edges, they haven't done this before. The Acer Freemanii is sporting new leafs that start red before turning green, this is also new.

 

What is the theory behind the regular iron sulphate application?
What is the application rate?
Do you scatter the solid material or water on a solution?

 

My problem was that trees that were supposed to turn red in autumn were not doing so.

After asking at a couple of different arboretums what the problem may be, it was suggested that i water in an application of sulphate of iron every month for a year by more than one nurseryman at different arboretums. I started this October 2023.

Turning the soil around the trees slightly acidic.

Level teaspoon per STD watering can full of water per square metre and i'm doing 4sq mtrs per tree'ish.

 

Soil is light and free draining. Not done a PH test and i live in an area where nearby fields sport a lot of chalk after being ploughed and there are several nearby nature reserves set aside for chalk loving wild flowers and orchids etc.

Done PH tests before in previous gardens and not found the results all that helpful to be honest, as some plants sometimes break the rules and do well where theoretically they shouldn't. My Camellia, azaleas and skimmias are doing OK, my pieris, not so well. Strawberries not doing as well as they have in other gardens i've had. My gooseberries have had a dose of Sulphate of Iron this year and are sporting a lot more fruit this year, but it's been wetter too, so who knows.

So, a more alkaline soil.

 

So how does a slightly more acidic soil affect the autumn colour?
My understanding was that it was more related to the difference between day and night temperatures. Also helped by a good hot summer.
The chlorophyll is broken down and taken back into the plant, leaving behind the carotenoid and anthocyanin pigments which give the autumn colours. These are masked by the chlorophyll over the summer.
You might find this interesting Poor autumn colour / RHS Gardening
and Fall Color Change Chemistry also Science of Fall Colors | US Forest Service

 

Having seen New England in the Fall, I can vouch for the local wisdom relating to best years for tree colour, being due to how hot summer was, and how cold nighttime temperatures are.

 

The Acers and Rowan will certainly prefer neutral to acidic soil [can't comment on Liqidamber] but constantly fighting the type of soil you have won't be ideal.
Prunus, of any type, aren't particularly bothered by soil type, but I'm not sure many people buy them for autumn colour.

You certainly need cooler temps at the right time to encourage the colouring in foliage. Acers weren't as vibrant here last year because autumn took ages to get cooler.
August is normally an autumnal month here where I am, rather than a summer one, and many trees/shrubs start changing by later in that month and into early September, but it's getting noticeably later each year.

 

Yes, weather plays a large part in the process each year. There are good years and poorer years.

"The chlorophyll is broken down and taken back into the plant, leaving behind the carotenoid and anthocyanin pigments which give the autumn colours. These are masked by the chlorophyll over the summer."

I'm no expert whatsoever and i'm thinking that an application of Sulphate of Iron doesn't help the tree turn a variety of colours in the autumn directly, but rather it changes the chemistry of the soil in a way that the tree draws up more of whatever causes the development of the carotenoid and anthocyanin pigments in the leafs. For the years 2021, 2 & 3 i had no colour in the leafs whatsoever, spring, summer or autumn. This year's (2024) new growth in the spring and new growth now is sporting initial colour (Reds & Oranges) before turning a much darker green than in previous years.

So i'm guessing that whatever creates the pigments created by the presence of carotenoid and anthocyanin is now being taken up by the trees.

This may be total tosh, of course! I'll have to wait until the autumn to find out, i'm sure that if i do get autumn colour this year, then some would argue that the application of Sulphate of Iron played no part.

My problem was that "i had no colour at all" when the same species / variety of tree elsewhere in my wider district where i live changed colour very well this last two years in a row.

These trees were all bought specifically for autumn colour (Except the Prunus which was bought for the spring flowers and some autumn colour).

I was assured that a monthly treatment for one year would be enough to last a few years. It was suggested that after the first year i could try doing it March, May and July.

I want autumn colour and if it's not possible then they'll have to go and be replaced with something more wildlife friendly instead as Acers and Liquidambers offer very little for our wildlife.

I have planted wildlife friendly trees already, i'll just have more of them if the Acers, Maples and the Liquidamber don't perform within the next couple of years. Trying to create all year round interest and colour, these trees are a significant part of that plan.

 

You seem so obsessed with autumn colour, I'm not sure anything will live up to your height expectations. Isn't gardening the ultimate in wishful thinking? We all have visions of what we'd like our garden to look like but sometimes nature has other ideas. Wouldn't it be better to just enjoy your healthy trees for what they give you year round and relax a bit about what happens for one month in the autumn? And frankly every tree is wildlife friendly as it offer shelter for countless creatures.

 

Carotenoids and anthocyanins are organic molecules and only contain hydrogen, carbon and oxygen with maybe some nitrogen thrown in. The availability of these would not be affected by soil pH.

Just wondering when you planted them and how old the trees were when planting, it could be an age/settling into new home related issue.
I'd be inclined to discount 2022 as it was very hot and dry that summer.
My Japanese maple, cheapo seedling, was a fantastic dark red from the start the only issue has been that dry cold winds scorch the edges of the leaves.

 

Thank you for your words.

Of course all trees have something to offer, however i do want something that offers autumn colour. If these trees can't offer autumn colour then i'd rather have trees that offer blossom, then either fruit or berries giving more for the benefit of birds and other critters.

The garden has plenty of Spring and Summer interest and does provide for pollinators and birds all year. Some blossom and flowers are bird and pollinator friendly specifically, some are for my benefit too with little benefit for the birds etc.

At the moment, these trees are not offering either me or wildlife very much. A different species of tree could offer a great deal more. I would also benefit from increased wildlife to see and watch in the garden.