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Paulownia / Sitka Spruce (PH)

Just wanted to set the record straight when it comes to replanting a Sitka Spruce forest with Paulownia or other deciduous hardwood, and also non-deciduous Eucalyptus.

More info and buy Paulownia

A Sitka Spruce forest and indeed most conifer forests have a soil PH of around 4 to 5.7, which is acidic

PH scale

Paulownia require a PH of at least 5, and grow best. and their range, between 5 and 8.5 is towards the neutral level.

It fair to say that my small Paulownia plantation isn’t in the idea spot, being North facing. Paulownia definitely like full sun and I’d also say high summer temperatures. Hydration can also be an issue, Paulownia like a lot of hydration, but don’t like having their roots in soaking soil. Paulownia are not a tree for the bog !
On a South facing slope with full sun and some shelter from severe, cold winter gales, I’d say you will have much more success and a couple of fellow enthusiasts here in Ireland have specimens which have grown three metres in a season.
Even with the disadvantages of my site, I am an enthusiast and they are growing. I’m very much looking forward to the flowers which I’m sure the bees and other pollinators will love.

One FaceBook comment I read recently suggested that in order to get good constructional timber from Paulownia, winter frosts are required to firm up the wood. The comments on the post also stated that their are hundreds of hybrids, bred to suit every environment and local, though as above my research suggests the PH must be above 5.
My impression from the four plus years I have been researching and growing; and do add any knowledge you have in the comments, is that Paulownia do best with high summer temperatures. They grow well in Southern Europe, producing the high value, quality timber Paulownia are renowned for. I doubt they have severe winter frosts in plantations in Spain, so as with all research there are contradictions.
My strong advice ! plant a small experimental forest and draw your own conclusions 😉

I’m definitely keen on experimental forestry 🙂
I like native species, Oaks, Ash, Beech and Sycamore which aren’t native, though mostly all broad leaved deciduous trees are considered fabulous by the anti non-native advocates 🙄

Anyway, the Robinia Pseudoacacia haven’t done well here, not even close, so I won’t be continuing with them. The advantage of planting small has meant I’ve learned without expending a lot of resources, time and money to find out they just aren’t suitable in my particular local.

Difficult to get a focus, but I’m sure you get the gist of it, hardly surviving, far less thriving 🙁

Bog Lizard - Robinia Pseudoacacia 071023

I did take a chance on the Eucalyptus, though there are so many varieties; some have done better than others, and after five an a half years I have reasonable knowledge of what grows best in my particular local.

Your very specific site local is the be all and end all from what I’ve gathered over the time I’ve been planting and researching.
I’m sure Viminalis would be great further inland away from the severe, possibly salty Atlantic gales, though I am at least six kilometres away from the shore. Prone to wind burn here which has hampered their growth, they can grow at three metres per year in ideal conditions, you’d be harvesting firewood in five years at that rate.
Viminalis were very frost hardy and survived the server cold snap at the end of 2022 with ease. the winter of 2022 / 23 didn’t have any severe gales and they have faired much better as a result.
Nature and climatic conditions are not static, they fluctuate.

Lush new top growth in October, the more mature leaves survive the gales, though new tender growth is susceptible to wind burn

Bog Lizard - Viminalis lush top growth 071023

In just over five years; fabulous wind protection for my property, something that didn’t cross my mind when I planted them

Bog Lizard - Eucalyptus protecting house 071023

My most sturdy Viminalis

Bog Lizard - Eucalyptus Viminalis trunk 071023
Bog Lizard - Viminalis full tree 071023
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Are paulownia invasive ?

Bog Lizard - Paulownia invasive ?

Before I planted any Paulownia on my small area here in West Clare, Ireland, I did a couple of years of research, and although I had heard a few references here and there to their invasiveness, I couldn’t find any actual evidence that they are.
Certainly not in Ireland or cool temperate climates.

The climate can be a bit of a downside in Ireland; my feeling (not backed up by research) is that Paulownia do best in climates that have hot summers, 30℃ plus.

This said, a couple of fellow enthusiast have said, that with full sun and good husbandry, their Paulownia have grown three metres in one season.

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Paulownia Clones or Seed grown 🤔

It’s certainly the case that seed grown trees will be genetically more diverse than clones, a fact !

For commercial plantations the advantages of clones, especially for Paulownia which are very easily cloned are appealing. Clone the fastest growing most productive trees and you get a higher return on your investment more quickly.
I haven’t heard of any downsides so far, though if all your trees are genetically identical, and they turn out to be susceptible to a specific disease or pest, then all of your investment is in jeopardy, where as with genetically diverse forests, it is more likely that some will survive.

In the video below I associate Ash Dieback with newer plantations and my hypothesis is partially correct as the Teagasc report indicates.

The fungal pathogen Hymenoscyphus fraxineus:

  • Originated in Asia
  • Affects younger trees more, hence my assumption that it was only affecting newer forests. This is not the case, though older trees are less affected.
  • Plantations in wetter ground are more susceptible.

So although I perhaps didn’t get my points across accurately, I’m happy to stand by the thrust of my argument, i.e. genetically diverse forests have at least some chance of surviving.
Teagasc is carrying out research to establish a gene bank of Die Back resistant Ash trees.

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First Paulownia tree planting

As I say in the video, I will be planting four rows:

  • Pao tong
  • Nord Max
  • Shan Tong
  • Tomentosa

for firewood, as a wind break / shelter, and for the flowers in a few years time. Also has to be said that it will be another section of grass on a tricky sloping area that I will no longer have to cut 🤣 I will sow it with wild flowers 😉

I’m hoping that the smelly organic fertiliser will deter the Hares and other herbivores from dining on them !

I’ve been researching Paulownia for a couple of years now and they are impressive. Europe seems to be particularly keen on them. I’ve watched videos from Italy, Spain, Eastern Europe and Germany. Paulownia will do well on moderately fertile ground and at high altitude. Most are very frost tolerant and those that I had outside here during what weren’t particularly severe frosts during the 2020 /21 winter, -4℃, though they were prolonged, were mostly fine. They don’t like getting their roots soaked for too long, not a tree for the bog, though they do like hydration during the growing season.

Those in the video below are fourteen months old from planting and look to be around four metres tall 😮 though those I have spoken to here in Ireland say that they aren’t getting anywhere close to this sort of growth. So I am trialing and will keep you posted 😉

The Paulownia in the video below are three years old.
Outstanding growth 😮 I have planted more, and intend to plant a few more in the next few weeks, even though it is getting quite late on in the growing season.