Most of us have never had to think seriously about how much food to grow to sustain a family long-term. The supermarket has always been there. But supply chains are more fragile than they appear, and the question “what would we eat if the shops closed?” has a surprisingly complicated answer — one that most people get spectacularly wrong the first time they try to work it out.
A food stockpile matters. In the first weeks, and possibly the first months of a serious disruption, stored food buys you time, stability, and the space to think clearly. But a stockpile has a bottom. Once it’s gone, it’s gone – and without a seed library, there is no long-term future. Seeds are where food security actually begins, and knowing you need them is only the start. Knowing exactly which seeds, and precisely how many, is where most people have no answer at all.
This article is for households who want to move beyond vague reassurances and understand what genuine long-term food self-sufficiency actually requires – not as a doomsday scenario, but as a practical question worth answering honestly.
Why Six Months Changes Everything
Short-term disruptions – a storm that closes roads for a few days, a local shortage that empties shelves for a week – are manageable with a well-stocked pantry. Most emergency preparedness guidance focuses on this range: two weeks to a month of stored food is the standard recommendation from organisations like the US Federal Emergency Management Agency and the Red Cross. Stock up, rotate your tins, know where your torch is.
But six months is a different problem entirely. At that timescale, stored food runs out. You are no longer managing a gap – you are managing production. And that means growing things, which means seeds, soil, space, time, and a realistic understanding of how many calories a plant can actually provide.
The gap between what people imagine they could grow and what they would actually need is, for most households, a factor of ten. Not two or three. Ten.
The Calorie Problem
An adult needs roughly 2,000-2,500 calories per day to function. Growing food is physical work, so the real figure for someone actively cultivating land is closer to 2,500-3,000 calories. Over six months, that’s somewhere between 450,000 and 550,000 calories per person – before you account for children, who need proportionally less, or teenagers and working adults, who often need more (and not forgetting any pets, too!).
Now consider what a typical vegetable garden produces. A well-tended allotment of 250 square metres – a generous plot by UK standards – might yield a meaningful variety of vegetables across a season. But variety is not calories. Courgettes, salad leaves and tomatoes are nutritious and welcome, but they are not calorie-dense crops. You cannot eat your way to 500,000 calories on runner/snap beans and cucumbers.
The crops that actually sustain people over long periods are the unglamorous ones: potatoes, dried beans, wheat, oats, and squash. The USDA’s nutrition data makes this clear – a kilogram of dried lentils contains around 3,500 calories. A kilogram of courgette contains around 170. These are not similar food sources from a survival perspective.
What a Six-Month Food Plan Actually Looks Like
For a family of four (two adults, two children) to meet their calorie needs for six months from home-grown food, a realistic plan needs to include:
- A significant area of calorie-dense staples – potatoes alone might require 200-400 square metres depending on yield
- Legumes for protein – dried beans and peas store well and provide essential nutrition alongside carbohydrate crops
- A surplus buffer of 20-30% above calculated needs, because yields vary with weather, pests, and disease
- A climate-appropriate crop selection – what grows reliably in southern England is not what grows reliably in the Scottish Highlands or Northeastern USA.
- An honest accounting of losses: germination failures, slug damage, blight, wind, and storage rot all reduce what you actually eat
The land requirement surprises most people. A family of four attempting to meet 100% of calorie needs from crops is typically looking at somewhere between 1,000 and 2,000 square metres (a quarter to half an acre) of productive growing space, depending on the crops chosen, the climate zone, and the skill of the grower. That is not a large allotment. That is a serious smallholding.
Calorie-Dense Crops vs. Common Garden Crops
A productive garden can provide valuable nutrition, but not all crops carry the same weight in a long-term food plan.
| Crop | Calories per kg | Food Value | Why It Matters |
|---|---|---|---|
| Oats | ~3,800 | High | Dense calories, stores well, and can provide a reliable staple where climate and space allow. |
| Dried Beans | ~3,400 | High | Important source of protein and calories; stores well when properly dried. |
| Potatoes | ~770 | High | High-yield staple that can produce meaningful calories in a relatively small area. |
| Winter Squash | ~260 | Moderate | Stores well, but is lower in calories than grains, beans, and potatoes. |
| Tomatoes | ~180 | Low | Nutritious and useful for meals, but not calorie-dense enough to carry a food plan. |
| Cucumbers | ~160 | Low | Hydrating and easy to grow, but very limited as a survival-calorie crop. |
| Lettuce | ~150 | Low | Helpful for freshness and variety, but too low in calories to be a primary food source. |
Practical Steps You Can Take Now
Understanding the scale of the problem is the first step. The second is making meaningful progress towards it, even without a smallholding.
1. Build a stored food baseline
Before thinking about growing, think about storing. A three-to-six month supply of calorie-dense staples – dried pulses, rice, oats, tinned fish, cooking oils – buys time and reduces the pressure on what you grow. Rotate stock regularly and store in cool, dark conditions.
2. Prioritise calorie crops over variety
If you already grow food, shift your patch towards calorie density. A bed of maincrop potatoes or dried borlotti beans does more practical work than the same area of salad crops. Both have their place, but in a planning context, calories come first.
3. Know your growing zone
Not all crops perform equally everywhere. Sweetcorn that thrives in the middle of France struggles in Ireland. Understanding what your climate zone supports reliably – and planning accordingly – is more valuable than optimistic seed catalogues. The Royal Horticultural Society’s grow-your-own guidance is a practical starting point for UK growers for instance.
4. Account for losses honestly
Plan for things to go wrong. A 20%-30% buffer on top of the calculated need is a reasonable starting assumption. Experienced growers who know their land and pests can reduce this; beginners should increase it.
5. Think in seeds, not plants
When planning a serious growing operation, seeds are the unit that matters. Not plants to buy from a garden centre, but seeds to store, germinate, and grow from scratch. Knowing how many seeds you need, for which crops, in what quantities, for your specific group size – this is where abstract planning becomes concrete action.
Doing the Math Properly
Working all of this out by hand – scaling calorie needs by group composition, adjusting for climate zone, accounting for loss rates, converting target calories into seed quantities – is genuinely complex. The variables interact in ways that make back-of-envelope estimates unreliable.
If you want to run the numbers properly for your own household, Food When the Shops Stop is a free calculator built specifically for this purpose. It works through your climate zone, group composition, activity level, crop selection, and loss rates, then produces a printable seed plan showing exactly what to buy and how much to sow. The calculator covers 55 calorie crops across 8 climate zones, alongside livestock and wild food sources for those who want to model a more complete picture.
It won’t make the growing easier. But it will tell you, clearly and honestly, what you’re actually aiming for.
Frequently Asked Questions (FAQ)
How much food does a family of four need to grow for six months?
A family of four – two adults and two children – needs roughly 1.5 to 2 million calories over six months. From crops alone, and allowing for losses, this typically requires between 1,000 and 2,000 square metres of productive growing space, planted predominantly with calorie-dense staples like potatoes, dried beans, and grain crops.
What are the most calorie-dense crops to grow?
The highest calorie yield per square metre comes from crops like potatoes, dried beans and lentils, sweetcorn, oats, and winter squash. These should form the backbone of any serious food-growing plan. Salad crops and many vegetables are nutritionally valuable but too low in calories to be relied upon as primary food sources.
How long would it take to become food self-sufficient?
True food self-sufficiency from growing alone takes years to achieve, not months. Soil health, seed-saving skills, knowledge of local pests and disease, and experience of crop failure all take time to develop. The realistic approach for most households is a combination of stored food and growing capacity, built up gradually over several seasons.
Do I need a large garden to grow meaningful amounts of food?
For short-term supplementation, a small garden makes a real contribution. For long-term calorie production, meaningful scale is required – typically several hundred square metres at minimum. Understanding the gap between what you have and what you’d need is more useful than assuming a kitchen garden will carry you through a serious disruption.
How do I account for crop failures in my planning?
A 20-30% surplus buffer is a reasonable baseline assumption. This means planning to grow 20-30% more than your calculated needs, to allow for germination failures, pest damage, disease, and storage losses. Experienced growers who know their land may need less buffer; beginners should plan for more.
Is it worth keeping livestock as part of a food plan?
A 20-30% surplus buffer is a reasonable baseline assumption. This means planning to grow 20-30% more than your calculated needs, to allow for germination failures, pest damage, disease, and storage losses. Experienced growers who know their land may need less buffer; beginners should plan for more.
