But it's a muted kind of joy, as he's also in the process of culling the more than 50 per cent of his crop destroyed by eight or so months of frequent rain.

He and his wife, Barbara, plan to open on schedule, and don't want this to be a sad story. They don't even want it to be a joyful story.

They really want it to be a story about climate change.

Several years ago, Keng and Barbara - "we like to call ourselves 'Barbie and Keng'!" - lost half of their crop due to drought.

Back then, the trees went brown all over as they dried out and died. This year, the brown has come from the roots up, leaving the tops of the trees green.

"The tree dies from the bottom," Mr Tan said. "I first noticed it two or three months ago. I thought at first it was a disease, because some were all fine and others weren't. But then we realised it was all the water."

Just up to road, Ziggy Kominek, who runs Santa's Shaped Christmas Tree Farm, is also contemplating his newest plantation of pines.

He recently planted around 10,000 saplings; 7500 have already died, due to excessive rainfall.

Meanwhile, the trees ready for harvesting in this year's crop, while still standing, are smaller than usual.

"The other problem, apart from the rain, is the lack of sunlight," he said. "They're not growing."

The pine trees - Pinus radiata, or Monterey pines native to the central coast of California and Mexico - take three to four years to mature into Christmas-worthy candidates.

Mr Kominek has his trees planted on "undulating land" which, he says, allows them to breathe and means his ready-to-pick crop has fared better than others.

But he's just as worried this season about the state of the paddocks, which look liable to bog any cars that come driving through - usually many dozens over the December weekends.

He has an order of gravel on its way, but just a few days out from opening on November 26, he can't find a truck driver willing to risk being bogged while delivering it.

Still, he's optimistic about opening for business this weekend.

"In three or four years' time, we'll have a problem, but at the moment we're okay," he said.

Unlike Mr Keng, he ran a sheep farm before deciding to switch to pines. He did an advanced diploma in farm management, "and then I read up about Christmas trees".

"I planted my first trees in 2000, and opened in 2004, and only sold about three trees, because I had no marketing," he said.

Nowadays, he runs a right commercial operation, open five days a week for families to come in and choose a tree, as well as supplying trees to various outlets around town, including Bunnings in Gungahlin, the Bus Depot Markets in Kingston and the weekly farmers market at EPIC.

Christmas Tree Keng, meanwhile, has also become a familiar destination for hundreds of Canberra families come December, who rock up ready to select a hand-pruned tree.

For a flat fee - this year it's $80 - customers collect a handsaw at the main shed, and drive around the plantation until they see a tree they fancy enough to cut down and take home. This year, the pickings will be slimmer, and will likely get even more so in years to come.

Malaysian-born Mr Tan migrated to Australia in 1970 to study forestry at the Australian National University, and spent his career in the public service.

It was his forestry training that led to the careful preparation of his plantation, contouring the terrain and installing contour riplines to catch rain, a useful measure in drought-prone areas like the Canberra region. But now those same riplines have caused the pine roots to effectively drown.

Both Keng and Barbara joke that "people must think farmers are never happy!".

But no matter how rigorous your training or slick your marketing, nothing can prepare Christmas tree farmers - or any farmers - for the weird and wild weather brought by climate change.

With fires, smoke, COVID lockdowns - the Tans also run a farmstay on their property - and now, endless rain, things have been hard.

"The work is hard, but opening up is always a happy occasion," Mr Tan said. "It's a part of family life, and we have customers who've been coming since they were tiny kids ... We used to measure their heights against the trees over the years."

But he's thought more than once of selling up and retiring properly.

"I don't want to turn into a grumpy old man," he said.