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“Empty shelves? Grow your own fruit and veg!” promised a headline on my feed. According to another, “Thousands of families are planning to become more self-sufficient” as “millions take up the Good Life”. No garden, no problem! “Try sprouting seeds, aka microgreens, like alfalfa, broccoli, amaranth and wheatgrass on wet kitchen roll.”

Urged on by a slew of such suggestions, unprecedented demand for fruit and veg seeds (up as much as 1800 per cent year-on-year) has caused many online sellers to freeze all new orders and set up long waiting lists. As someone who has been obsessed with growing your own for decades, it is so exciting to see this surge in interest. But how realistic are the promises that such efforts will help you along your way to self-sufficiency? Let’s do the maths.

If your goal really is to feed yourself, it would be hard to find a better crop than potatoes. In terms of calories per unit of land, they are easily the most productive crop that can be grown, at least in the UK. Churning out yields of approximately 4 kilos per square metre on UK farms, according to the Agriculture and Horticulture Development Board, they produce more than three times the calories of wheat, for instance. Spuds also happen to be one of the crops with the most balanced nutrition, meaning humans can survive for at least a year eating very little else, according to the International Potato Center in Peru.

So how much land would you need to feed yourself, given the single most calorifically efficient crop it is possible to grow? Well, based on the UK National Health Service’s recommended average adult intake of 2250 calories a day (2000 for women, 2500 for men), your plot would need to generate 821,250 calories a year. That’s around a tonne of spuds, requiring 266 square metres of land.

Now, it is tough to pinpoint reliable stats for the size of a typical UK garden, but a 2017 survey by the estate agent Foxtons found they average just 3.7 square metres. So even assuming that, as a first-timer, you could give professional agronomists a run for their money and produce identical yields to industrial farms, this would give you enough calories for only around 5 days. As an adult male, this is just over 1 per cent of my annual needs. Not exactly ideal.

“If your goal really is to feed yourself, it would be hard to find a better crop than potatoes”

Ah, but what if you had an allotment? Things are looking up here. The average UK allotment is 250 square metres, which coincidentally almost matches the required land to feed yourself on spuds. But there are still problems: waiting lists for an allotment in some parts of the UK are years long and even if you can get one, it can provide enough calories for you, but not for anyone else in your family.

OK. So maybe I am being unkind as to what those headlines are actually promising. Perhaps by self-sufficiency they don’t mean calorie-wise, but just in terms of fruit and veg requirements? Working on World Health Organization guidelines stating that adults need at least five 80-gram servings of fresh produce a day to maintain health would mean each of us requires 146 kilograms every year. While vegetable yields vary, for a family of four, this would mean a minimum of 292 square metres for lower weight crops like lettuce and about 84 square metres for heavier ones like apples.

But let’s not forget, these crops are highly seasonal, and storing them to last the whole year will be tough. Even with some of the world’s best experts at post-harvest storage and vast climate-controlled warehouses, millions of tonnes of food is lost by industrial agriculture in the UK each year. A rack in your garage or a fancy chest freezer simply can’t compete. And when can you expect this harvest to roll in, given its promise to solve the problem of empty shelves now? With most veg crops, if you start right now, you might get a harvest around mid-July. With fruit, it will be sometime in autumn 2021 to 2025.

As for the “no garden, no problem” alfalfa sprouts solution, to get your daily veg requirement from these, you would have to sow 1 square metre every day. As they can take seven days to mature, that would mean up to 7 square metres of your home, per person, dedicated to them. To meet your calorific needs from them, you would require 230 square metres on the go at any one time, all year round. That is a lot of kitchen roll!

Is growing your own great exercise, a chance to get fresh air and a welcome distraction in these uncertain times? A resounding yes. Does it teach invaluable lessons about where our food comes from, while giving an edible bonus? 100 per cent. But is it likely to provide beginners with even a passing semblance of self-sufficiency, as the headlines promise? I’m afraid not. So enjoy your garden (if you have one) for all the benefits it provides, but take the promise of “the Good Life” with a hefty pinch of salt.