"I'm over here!" shouts Kate Humble, and she of Springwatch and Lambing Live gambols towards me, closing the gate on a field of anxious goats and their Disney-cute babies. She's carrying a bucket. "I was just about to muck out," she announces, and I'm reminded this is a working farm in the Wye Valley and in no way a TV set.

The photographer has already done his work and gone. Apparently Humble had no idea he was coming. It is hard to think of another TV person on the planet for whom an impromptu photoshoot while wearing a well-loved fleece and no makeup would be OK, but Humble couldn't give a hoot. She's been up since the wee small hours: "I love getting up early. I can bounce out of bed at 5am but I'm useless at night."

She leads me to a kitchen, which doubles as the HQ for Humble by Nature courses on animal husbandry and rural skills, from foraging to building an outdoor pizza oven. Her assistant Rebecca wonders if I'd be OK with some old coffee heated up in the microwave. I'm wondering how to explain that although I'm against food waste, there are limits. "No! That sounds disgusting," says Humble, even though she's a green tea drinker. "Make some new!" It's an earthy introduction.

Kate Humble has been the poster girl for a particularly immersive brand of popular science and wildlife programming for the last 15 years. Behind the scenes TV executives are full of admiration for her prowess at delivering live broadcasts (one tells me she has a photographic memory) and her ability to pull in the viewers. Lambing Live is an unlikely hit on paper, but it has proved to be a ratings juggernaut, pulling 2.5 million viewers, even on a Friday night. What you get as a viewer is her warmth and natural curiosity. She gets right in there, sometimes quite literally; her inspection of a ram's testicles on the most recent series of Lambing Live caused quite the Twitter frenzy.

Much has been made of her decision to be child-free too. She rightly thinks it's rude of journalists to pry about this. But then she brings the topic up quite naturally, so I feel at liberty to ask her how she feels about those who think your environmental conscience only really forms when you have kids. "I think one of the most environmentally friendly things you can do is NOT have children," she says. "Yes, I know we have an ageing population but I've got a great plan for my old age, which is a return to communal student living. The idea that people have to have children before they wake up to the idea that the world might not be a great place in 15-20 years' time is nonsense. I'm not particularly clever, nor brilliant nor insightful but I don't need to have kids to tell me that. I've got godchildren. I don't know why: I'm woefully unqualified on both parts of that equation – can't be a mother, don't believe in God. But you know, I want them to have a world that's functional and great to live in."

It's only when you observe her on home territory – now a 117-acre former council farm in Trellech, Monmouth, that you realise just how far this natural curiosity has propelled her. Keeping sheep is famously hard work. They are ingenious at finding ways to die. Almost anyone who observes them up close is put off. Humble was completely seduced.

"After I did the first series [of Lambing Live] I desperately wanted to keep sheep. It's the herding instinct that gets me. Most breeds of sheep are very cyclical creatures – it draws you in and brings you close to the seasons. I didn't just want a few pet lambs for the table, I wanted to do it properly and rear ewes. God, George Monbiot [who is famously anti-sheep] probably hates me."

The four acres she has up the road where she lives with her husband, TV director Ludo Graham, wouldn't accommodate these sheepy dreams, so they began asking around and found the working farm that we're now on. There were once 16,000 such council farms around Britain, small parcels of land rented out to farming families or individuals who didn't have their own land, but councils have spent the last decade selling them off for development. Humble estimates there are just 4,000 left.

The opportunity to "save" a farm fed into another strong belief. "Do we want everything to be imported, to deny our farming heritage, to get rid of every opportunity for young farmers?" she asks. "It's nigh on impossible to get into farming now, if you even wanted to." She once tried to buy a farm in the Karoo, South Africa, for £70,000 but was dissuaded by Ludo, who pointed out they knew nothing about farming. This time, however, she battled until she "won" it from the council and then almost fell into despair because she thought she'd never find a tenant farmer. Then she lucked out with local farmers Tim and Sarah Stephens, who breed Welsh mountain sheep and Hereford cattle and are now happily settled.

But it's the price of food, the farmer's end product, that really irks her. "Everyone's going to hate me and call me a middle-class bitch but I'm past caring because I'm so incensed. Food waste is endemic but we don't value food because it's not expensive enough. Four pints of milk for a quid, are you kidding me? And the reason we can buy that without thinking of the implications is because we're so disconnected from the land and farming process. People will see TV footage, like last year, of lambs being buried in the snow but then they'll complain about paying more for lamb. Here, we want to make that connection again."

Kate Humble with a fellow farm worker. Photograph: Stephen Shepherd

The farm has PV panels and a permaculture garden, they've planted 2,000 trees, the RSPB carries out an annual survey on bird life, and it's minimal-input, so why not go the whole hog and go organic? "Honestly, because it's a huge faff. And sometimes it's unrealistic. I want to make what we're doing as accessible as possible. I want people coming here on courses or visits to think 'I can do that' without a huge amount of land, money and paperwork. To all intents and purposes we're organic anyway."

We go back outside and examine a strange crescent-shaped building-in-progress that sums up Humble's irrepressible nature. Last year, while working on a BBC Scotland programme called the Great Big Energy Saving Challenge, which challenged six families to slash their energy use by a third in three weeks (they all managed a 50% cut) she visited the Passive House development on the Dormont Estate near Lockerbie. Here, talking to a German academic, she came across the idea of aquaponic food production, combining conventional aquaculture with hydroponics. Months on, she has secured a grant from the Welsh government and is midway through a £60,000 build that will see her launch the UK's first closed-loop aquaponics centre, producing fish and fruit and veg working with aquaponics specialist Charlie Price.

Using the same super-strong plastic that forms the Eden project's biomes, Humble and team are effectively creating an incredibly efficient heat pocket that requires no additional heating. "Obviously aquaponics isn't new," she stresses. "People are doing this in the UK already. But what is clever here is the marriage between hydroponics and aquaculture." In essence the two systems are symbiotic: as Humble explains it, "you've got your fish in your tanks – tilapia – shitting away merrily, and that water full of nitrates is pumped through vegetable beds. The leafy greens love the nitrates and grow like fury, the vegetables clean the water and back it goes to the fish."

The ecological stumbling block for aquaculture is usually the feeding of the fish – using dead fish. But she has an ingenious plan. "It's all about waste management," she says brightly. "As well as a wormery there's a biopod, a sealed unit containing a non-endemic species of black soldier fly. This is where waste goes that can't be composted. The flies lay eggs, grubs hatch, then they pupate and we harvest them. Voilà: fish and poultry food. It's totally self-sustaining and incredibly low-maintenance."

If it works, it could be a real coup. In German trials the system has showed capacity to produce 250kg of fish a year and 32kg of fruit and veg a week. "You would never need food banks again!" she says.

It must be cool to create your own specialised ecosystem. "It is! I love the idea that in order to create a sustainable harmonious working environment you need your predators and your prey, but there's so many people whose idea of a perfect world is one without insects or predators. I've made wildlife films where they don't really want to show anything killing anything. What's the point?

"I suppose this is like creating my own slice of a perfect world." We could call it the Humble Bubble.

An earlier version of the article stated that German trials of aquaponics showed capacity to produce 250kg of fish and 32kg of fruit and veg a year. This was amended on 18/04/2014 at 16.12.

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