How to Start an Urban Garden: Light, Pots, Compost and Costs
- University of Maryland Extension puts tomatoes, peppers and other warm-season crops at 6 to 8 hours of direct sun a day, and lettuce, spinach and other cool-season crops at 3 to 5 hours.
- The Royal Horticultural Society advises containers at least 45cm (18in) deep and wide for vegetables, because smaller pots need far more frequent watering and feeding.
- Loose-leaf lettuce can be ready to pick four to six weeks after sowing, which makes salad the quickest return on a pot of compost.
- A three-container starter set-up is likely to cost £40 to £85 in the UK or $65 to $120 in the US, and most of that buys pots you will reuse.
- Balconies have weight limits. The RHS advises placing heavy containers near load-bearing walls and taking professional advice before loading a roof.
Most first attempts at growing food in a flat or apartment fail for one of three reasons: the spot was too dark for the crop, the pot was too small, or the watering was erratic. None of those is about talent. All three can be settled before you spend any money.
This page is the starting point for the urban garden section, for readers in the UK and the US. Where a topic deserves more room, such as what fits on a windowsill or how to get pots through a heatwave, there is a link to the post that handles it.
How much sun does an urban garden need?
Light decides what you can grow, so measure it first. On a clear day, check your space once an hour from about 8am to 6pm. Note whether the sun falls directly on the spot where a pot would sit, then add up the hours. Bright shade does not count.
Repeat the count in another season if you can. A balcony that gets seven hours in June may get two in October, once the sun drops behind the building opposite.
University of Maryland Extension gives 6 to 8 hours of direct sun for warm-season crops (tomato, pepper, aubergine or eggplant, squash) and 3 to 5 hours for lettuce, spinach and Asian greens. Illinois Extension defines full sun as at least six hours and partial shade as four to six.
Under three hours, food growing gets hard. The RHS list of crops for shady spots includes chard, spinach, coriander and alpine strawberries, so a dim balcony still has options. A sill with no direct sun at all is a job for microgreens or a grow light.
Upper floors add two complications. The RHS names strong wind and strong sun as the main limitations of balconies and roof gardens, and says plants there often need watering twice a day in summer. That is worth knowing before you fill the space.
What size containers should you buy?
Bigger than you think, and fewer of them. A large volume of compost holds more water and nutrients, so the plant survives a missed watering. The RHS guide to vegetables in containers recommends a depth and width of at least 45cm (18in), and says anything smaller will need frequent watering and feeding.
US extension services work in gallons. The table puts the two systems side by side. Litre conversions are rounded, and one US gallon is about 3.8 litres.
| Crop group | Minimum volume | Minimum depth | Examples |
|---|---|---|---|
| Small | 1 to 3 US gallons (4 to 11 litres) | 10 to 15cm (4 to 6in) | Basil, coriander (cilantro), radish, spinach, salad leaves |
| Medium | 4 to 6 US gallons (15 to 23 litres) | 20 to 30cm (8 to 12in) | Dwarf tomatoes and peppers, beans, beetroot, larger herbs |
| Large, one plant per pot | 8 to 10 US gallons (30 to 38 litres) | 30 to 40cm (12 to 16in) | Full-size tomatoes, peppers, aubergines, cucumbers |
| RHS rule of thumb for vegetables | A pot 45cm (18in) wide and deep, roughly 40 litres or 10 US gallons | 45cm (18in) | Anything you do not want to water twice a day |
The first three rows come from Maryland's page on types of containers. RHS crop pages are more generous at the small end: at least 20cm (8in) wide and deep for basil, 25cm (10in) for parsley and 30cm (12in) wide for salad leaves. When in doubt, take the larger figure.
Material matters less than size. The RHS notes that for small containers, plastic, metal and fibreglass lose less moisture than terracotta, although metal heats up in sun. Every container needs drainage holes, and a recycled bucket is fine once you have drilled some. Fabric grow bags are cheap, light and fold flat, which suits renters.
Which compost or potting mix should you use?
Use bagged potting compost, not soil dug from a garden or park. The RHS advice for containers is a sterile, peat-free multi-purpose or container compost. For long-term pots such as rosemary, it describes peat-free John Innes No 3, a soil-based mix, as especially easy to manage.
In the US the equivalent product is labelled potting mix or container mix. Illinois Extension notes that some mixes contain no fertiliser at all, so read the bag.
Where the UK stands on peat
Peat extraction damages bogs that store large amounts of carbon. In August 2022 the UK government announced a ban on retail peat sales to amateur gardeners in England by 2024, noting that bagged compost accounted for 70% of the peat sold in the UK. That deadline passed without legislation.
The RHS peat policy, updated in December 2025, says the charity is still pressing government to legislate. The RHS stopped selling peat-based compost in 2019 and moved its gardens, shows and retail to "no new peat" by 1 January 2026.
So peat-based bags may still be on UK shelves, and buying peat-free means reading the label. Peat-free mixes can look dry on top while still damp underneath, so check with a finger before watering. The US has no equivalent restriction. Many US mixes are peat-based, with coconut coir and composted bark the usual alternatives.
How often should you water and feed pots?
No timetable works. The RHS method for containers is to push a finger about a third of the way down the pot and water only when the compost feels dry at that depth. In a dry summer that may be every day or every other day. Light rain rarely reaches the roots.
Water slowly and thoroughly: fill to the rim, let it soak in, then repeat once. Early morning is best, since less evaporates. The RHS container maintenance guide calls overwatering the most common cause of loss of container plants, so damp compost means leave it alone.
Compost also runs out of food. Clemson Cooperative Extension estimates that a mix with added fertiliser feeds plants for eight to ten weeks. After that the RHS suggests a general-purpose liquid feed every two weeks. Tomatoes get a high-potassium feed every 10 to 14 days once fruits start to swell.
Hot spells have their own rules. Our guide to keeping container plants alive in a heatwave covers shade, mulching and what to do before going away.
What should you grow first?
Start with three crops that are fast, forgiving and useful in a kitchen. Three pots you look after will out-produce ten you resent.
Cut-and-come-again salad leaves
Sow a loose-leaf lettuce such as 'Salad Bowl', or a mixed leaf packet, in a trough at least 30cm (12in) wide. The RHS says loose-leaf lettuce can be ready in four to six weeks, and that each sowing of salad leaves should give two or three pickings.
One herb you already buy
On a sunny sill or balcony, grow basil ('Aroma 2' holds an RHS Award of Garden Merit) in a 20cm (8in) pot. In part shade, choose parsley or mint. Keep mint in its own container, because its underground stems spread through anything they share.
Radishes
Salad radishes such as 'French Breakfast' or 'Scarlet Globe' can mature in as little as four weeks from germination, in a pot 30cm (12in) wide and deep. They teach sowing, thinning and watering in a single month, which is a quicker education than a tomato.
Add one bush tomato once the basics feel routine. The RHS names 'Gold Nugget', a compact cherry variety, grown one plant to a 30 to 45cm (12 to 18in) pot. For crops matched to windowsills, doorsteps, balconies and shared yards, see the crop-by-space guide to very small spaces.
When should you start?
In the UK, salad leaves can be sown indoors from February and outdoors from mid-spring to late summer. Basil is sown indoors from March to July and goes outside in early summer, once nights stay above 10°C (50°F). Outdoor tomatoes are sown indoors from late March to early April.
In the US, work from your average last spring frost date instead of the month. The National Gardening Association's frost date tool gives first and last frost dates by ZIP code, using NOAA data. Lettuce, spinach and radish go in a few weeks before that date. Tomatoes, peppers and basil wait until after it.
The USDA Plant Hardiness Zone Map answers a different question: how cold your winters get, in 10°F zones and 5°F half zones. Use it to choose perennial herbs and fruit that survive outdoors. The November 2023 update moved about half the country into a warmer half zone.
If you are reading this in September or later, you have not missed the year. Garlic, broad beans, winter salads and spring bulbs all go in during autumn, and the autumn and winter guide gives the timings.
How much food will a balcony really produce?
Enough to change what you buy, not enough to change where you shop. I could not find reliable per-pot yield figures from the RHS or a US extension service, and the numbers quoted on gardening blogs rarely cite anything. What the official guidance does give is a sense of rhythm.
A 60cm (24in) trough of cut-and-come-again leaves gives two or three pickings per sowing, by the RHS estimate. Sow a second trough three weeks after the first and you have leaves most weeks from late spring to autumn. A bush cherry tomato starts ripening from midsummer.
The economics favour crops that are expensive by weight and spoil fast in the fridge: herbs, salad leaves, chillies. They do not favour potatoes, onions or carrots, which are cheap to buy and greedy for space.
One caution on compact plants. Clemson Extension notes that dwarf varieties often crop early, but most do not produce as heavily as standard ones. Expect modest harvests from a plant bred to stay small.
Be wary of any claim that a windowsill will cut your food bill by a set amount each week. It depends on what you were buying before. If a bag of salad was going slimy in your fridge every week, a trough of leaves saves you that. If it wasn't, it won't.
What does a starter set-up cost?
The table budgets a sensible first season: two 30cm (12in) pots or troughs, one 40-litre (10-gallon) container, compost to fill all three, seeds, two herb plants and a bottle of feed. These are my own planning ranges for mainstream garden centres and DIY stores, not quotes from a named retailer, so check local shelf prices.
| Item | What to buy | UK | US |
|---|---|---|---|
| Containers | Two 30cm (12in) plastic pots or troughs and one 40-litre (10-gallon) pot or fabric grow bag | £15 to £30 | $20 to $40 |
| Compost | 100 litres of peat-free multi-purpose compost, or two 2 cubic foot bags of potting mix | £12 to £20 | $20 to $35 |
| Seeds | Three packets: mixed salad leaves, radish, one more of your choice | £6 to £10 | $8 to $14 |
| Herb plants | Two young plants, such as rosemary and mint | £4 to £8 | $8 to $12 |
| Feed | One bottle of liquid tomato feed | £5 to £8 | $8 to $12 |
| Watering can | Any can with a rose, or a reused milk jug with holes in the lid | £0 to £8 | $0 to $10 |
| Total | First season | £42 to £84 | $64 to $123 |
As one checked reference point, Burpee listed 'Salad Bowl' lettuce seed at $4.45 for 1,500 seeds on 21 September 2026. That is several seasons of salad from one packet.
In year two the pots, the can and most of the feed are still there. You are buying compost to refresh each pot and a few packets of seed, so the running cost falls sharply. Skip self-contained hydroponic units, decorative pots without drainage holes, and any kit offering ten seed varieties before you have grown one.
Is your balcony strong enough, and are you allowed?
Wet compost is heavy. A litre of water weighs a kilogram, and as a rough working rule a litre of saturated compost weighs about the same. The set-up above holds around 70 litres, so allow roughly 70kg (155lb) once watered. That is one extra adult standing on the balcony permanently.
For most modern balconies that load is unremarkable. Ten large terracotta pots and a raised bed are a different matter. The RHS guidance on roof gardens and balconies warns that balconies suspended out from a building have strict weight restrictions.
The same page recommends placing heavy containers near load-bearing walls or over a beam or joist. It also suggests lightweight containers, and fastening pots down so that wind cannot tip them. Nothing should hang on the outside of a railing above a street or a neighbour.
When to ask before you plant
In the UK, read your lease or tenancy agreement for clauses on balconies, external alterations and items on railings. Ask the landlord, managing agent or freeholder in writing if it is unclear. For a roof terrace, the RHS advises using a chartered structural engineer or surveyor and checking whether planning permission is needed.
In the US, check your lease and any HOA or condo association rules, and ask building management for the balcony's rated load. For roof decks, ask a licensed structural engineer. In both countries, keep fire escapes clear and make sure water from your pots does not drain onto the balcony below.
Renters have one advantage: everything in a container is portable. Avoid drilling into walls or railings, use freestanding shelving and troughs that sit inside the rail, and the whole garden can leave with you.
Questions readers ask
Can you grow vegetables on a north-facing balcony?
Some. With under three hours of direct sun, tomatoes and peppers will disappoint. Leafy crops are more tolerant: the RHS lists chard, spinach and coriander among crops for shady spots, and says mint and parsley grow in partial shade. Expect slower growth and smaller harvests, and keep pots at the brightest edge of the balcony.
Do you need a grow light to grow herbs indoors?
On a bright south or west-facing sill, usually not between spring and early autumn. In winter most culinary herbs struggle, because a northern windowsill delivers far less than the six hours of direct sun they want. The autumn and winter guide gives the light figures and grow-light distances.
Can you reuse compost from last year's pots?
For salad, herbs and flowers, yes, with help. Tip it out, remove old roots, mix it with fresh peat-free compost and add fertiliser, because the nutrients will be spent. Do not reuse compost from a plant that died of disease. Give hungry crops such as tomatoes fresh compost each year.
Is it safe to eat food grown in a city?
Growing in bagged compost in containers avoids the main urban concern, which is contaminated ground soil. Wash everything before eating, as you would shop-bought produce. If you plan to grow in the ground and do not know the site's history, ask your council in the UK or your state extension service in the US about soil testing first.
Sources
- Royal Horticultural Society. Vegetables in containers; How to water containers; Container maintenance; Roof gardens and balconies; Best crops for shady garden spots. Grow-your-own guides: salad leaves, lettuce, radishes, tomatoes, basil. Accessed 21 September 2026.
- Royal Horticultural Society. RHS peat policy. Last updated 3 December 2025.
- Department for Environment, Food & Rural Affairs. Sale of horticultural peat to be banned in move to protect England's precious peatlands. 27 August 2022.
- University of Maryland Extension. Growing vegetables in containers; Types of containers for growing vegetables. Accessed 21 September 2026.
- University of Illinois Extension. Growing vegetables in containers. Accessed 21 September 2026.
- Clemson Cooperative Extension. Container vegetable gardening. Accessed 21 September 2026.
- US Department of Agriculture, Agricultural Research Service. USDA Plant Hardiness Zone Map; USDA unveils updated Plant Hardiness Zone Map. 15 November 2023.
- National Gardening Association. Frost dates calculator. Accessed 21 September 2026.
- W. Atlee Burpee & Co. Salad Bowl lettuce seeds. Price checked 21 September 2026.
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