After six years in Switzerland, he and wife Lucy decided to make the move when their daughter Tabitha finished primary school in Geneva. The couple also have a son, James, who now studies agriculture at college, while Tabitha is a dressage rider.
"We bought the farm in 2012, at the lowest point of the post-crash chaos," says Peter.
"It was a steep learning curve, but from five heifers that came with the land, we now have a small milking herd of 30 black-and-white Friesian cows.
"We also finish about 30 beef cattle a year, and continually buy in calves. We retain our milk and use it to feed calves.
"We've also been experimenting with making our own cheese for the past three years. However, we have quite a big surplus of milk now, so we may supply a creamery next year or the year after."
Peter works the farm himself, with help from son James, while wife Lucy runs her own manufacturing business, Le Bougie, a luxury perfume and scented candle company based in Belgooly, just outside Kinsale.
Like her husband, Lucy changed careers to become a professional perfumer when the couple moved to Ireland.
Before marrying Peter she was a personal chef for Hollywood stars and British royals, but took the opportunity in Switzerland to study her first love - perfumery. She opened for business in 2012.
Nicknamed 'Ireland's Jo Malone,' her high-end candles - with delicious combinations including Ginger and Black Pepper, Honeysuckle and Sea Salt, and Kaffir Lime and Samphire - are now stocked in more than 120 outlets nationwide.
Like more than half of Ireland's farming families, the Hagertys supplement their agricultural income with an adjunct business - a winning combination that enables them to enjoy the sweet smell of success, even if, says Peter, "Lucy might see the farm as the adjunct business!"
When Peter's trusty tractor started to stall last year, Lucy responded by introducing a new line of fragrances to help pay for a new one.
With a nose for business equal to her keen sense for scents, Lucy targeted a wider market for Crop Candles, pitching them at €16 compared with €25 for Le Bougie.
Inspired by the land and the elements, the new collection sold strongly and, just nine months later, Peter got his new tractor.
"The old Massey was on its last legs," he says. "It still is. It's been retired to light feeding duties, but thanks to Lucy's Crop Candles, I bought a New Holland - the price is a state secret.
"Seriously though, farming families tend to have a strong entrepreneurial spirit and a great ability to adapt, which are essential qualities for the lifestyle.
"There are always challenges to face on a farm. One for me is that the land is spread over 17km - the old tractor just wasn't up to it.
"And beef is a constant challenge, especially over a fragmented land space.
"This has been a shocking hard year with the weather. We were lucky during the storms that we were understocked, but the drought affected us really badly. We had less than half of the grass we wanted to grow, and are left with an appalling shortage of straw.
"We're experimenting with peat bedding, because needs must, but I don't think I'll be repeating it."
Peter and Lucy have ambitious plans to upscale synergies between both the farm and the perfumery business in the coming year. Subject to planning, they hope to open a shop and a café next to the factory in Kinsale.
"A perfumery is like a laboratory, and people are often fascinated to get a guided tour of the factory and see how candles are made," says Lucy.
"Visitors will be able to sample the different scents in the shop, and then sit down to a beautiful cup of coffee and a slice of cake. All the milk, cream, yogurt and cheese served will be from our own farm."
She's already named it the Crop Café, after the successful candles that helped pay for the new tractor.
"The Crop brand connects with the earth, and farming," she says. "Crop Candles celebrate nature, with year-round fragrances of earth, rain and grass. Seasonal scents include Elderflower, Rhubarb and Gorse for summer, while this winter we have Douglas Fir, Sloe and Seaweed.
"I know nothing about farming, yet I feel a deep connection with the land and never fail to be inspired by my surroundings. I try to capture the scents I get when I walk through the fields, like the sweet coconut smell of gorse flowers, or the slightly chocolaty fragrance that comes from rain.
"The senses of taste and smell are very similar, so for me, being a personal chef is not unrelated to hand-pouring artisan candles."
'I was told the queen was coming to tea'
As well as making scented candles and perfumes, Lucy Hagerty also creates bespoke fragrances for high-end hotels, including Dromoland Castle, Adare Manor and the Cliff House Hotel.
She's also tailoring a unique fragrance for a Hollywood star whose identity she's not at liberty to reveal. Confidentiality is par for the course for the woman who once catered for the highest circles of British royalty.
In her previous career as a personal chef, she worked for the Duchess of York, Sarah Ferguson, for three years in the 1990s.
"I was thrown in at the deep end," she says. "On my first day I was told that the queen was coming to tea. I hadn't time to be nervous and just set about making lovely sandwiches and cakes. I cooked for Her Majesty a few times, and I met Princess Diana often, because she and the Duchess of York were very close friends at the time.
"I loved being a personal chef, but it demanded a lot of travel and anti-social hours, so when the children came along, I gave it up. Now I'm doing what I've always wanted, and Peter is following his dream too. This time of year is extremely busy for me - I'm literally burning the candle at both ends.
"However, even if we're like ships in the night, with Peter on the farm and me in the factory, suppertime is a great time to catch up and talk about our day.
"We've been together since God was a child - we met as students in Oxford, and next year we'll celebrate our 25th wedding anniversary.
"We're a great sounding board for each other and we're always looking for new ways to use our milk. Last night we were planning ice cream."