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Companion planting you can see while you plan
A companion planting chart is only useful at the moment you decide where something goes. Niwa draws a green dot between squares that help each other and a red dot between squares that should be separated — as you place each plant, not afterwards.
The problem with companion planting is not a lack of information — it is that the information arrives at the wrong time. You read the chart in January, plant in May, and discover in July that the onions are sitting next to the beans. Niwa moves the check to the moment of the decision: place a crop, and the borders it shares with its neighbours turn green or red immediately.
Why proximity matters more in a raised bed
Traditional companion planting advice was written for row gardens, where “next to” can mean two or three feet apart. In a square foot bed, neighbouring crops are twelve inches apart and their root zones overlap almost completely. Both the beneficial and the antagonistic effects get stronger.
That cuts both ways. Basil genuinely does well tucked against tomatoes in a dense bed. Onions genuinely do suppress beans a foot away in a manner they would not at a metre. Intensive spacing is exactly the situation where paying attention pays off.
What the dots mean
Green dot
These two neighbours benefit each other — through pest masking, pollinator attraction, nitrogen fixing, shade or physical support. Keep them adjacent.
Red dot
These two compete, share a pest or disease, or one chemically inhibits the other. Move one of them at least a couple of squares away.
The pairings that carry real weight
Worth deliberately arranging
| Pairing | Mechanism |
|---|---|
| Tomato + basil | Basil's volatile oils disrupt the scent cues thrips and whitefly use to locate tomatoes |
| Carrot + onion (or leek) | Each masks the other's scent from its specific root fly |
| Beans/peas + brassicas | Legumes fix nitrogen; hungry brassicas following or beside them benefit |
| Any crop + marigold | French marigold root exudates suppress root-knot nematodes; flowers draw hoverflies |
| Any crop + borage or calendula | Strong pollinator and predatory-insect draw, especially for squash and beans |
| Lettuce + tall crops | Afternoon shade from tomatoes or beans delays bolting in summer heat |
| Corn + beans + squash | The Three Sisters: corn gives support, beans fix nitrogen, squash shades out weeds |
Worth actively separating
| Keep apart | Why |
|---|---|
| Onions/garlic ✗ beans/peas | Alliums inhibit the Rhizobium bacteria legumes rely on to fix nitrogen |
| Fennel ✗ almost everything | Allelopathic — it suppresses germination and growth in most neighbours. Give it its own container |
| Potato ✗ tomato | Both nightshades; they share blight and Colorado potato beetle |
| Brassicas ✗ strawberries | Direct competition, and brassicas tend to win |
| Cucumber ✗ aromatic herbs (sage, rosemary) | Strong aromatics are reported to check cucumber growth |
| Sunflower ✗ potato, beans | Allelopathic compounds plus heavy shade and root competition |
Being honest about the evidence: the physical mechanisms above — shade, scent masking, nitrogen fixing, pollinator draw, shared pests — are well supported. Claims that a companion improves another crop's flavour are folklore with little testing behind them. Niwa's dots stick to pairings with a plausible mechanism rather than to the full traditional chart. The reasoning per pairing →
Using companion mode while you plan
Place the big, fixed crops first
Tomatoes, brassicas, squash. These are the ones you will not want to move later, so let them claim their squares before the smaller crops fill in.
Watch the borders as each plant lands
Dots appear on the edges between the new square and each of its neighbours. A red dot is cheapest to fix in the second before you place the next plant.
Use herbs and flowers as buffers
When two crops must be near each other, a square of basil, marigold or calendula between them breaks the adjacency and earns its place as a pest deterrent.
Keep the allium block together
Onions, garlic, shallots and chives clash with the same things, so grouping them in one corner of the bed — far from the legumes — resolves most red dots in a single move.
Do a final sweep before you buy seed
Scan the whole bed for remaining red dots, then go to the calendar tab. Fixing the layout on screen costs nothing; fixing it in July costs a crop.
A conflict-free 4×4 arrangement
Grouping by family is the quickest way to a clean bed. This layout has no red pairings:
| Row (N→S) | 1 | 2 | 3 | 4 |
|---|---|---|---|---|
| North | Tomato | Tomato | Basil ×4 | Pepper |
| 2nd | Marigold ×4 | Lettuce ×4 | Lettuce ×4 | Calendula ×4 |
| 3rd | Carrot ×16 | Carrot ×16 | Onion ×16 | Onion ×16 |
| South | Beetroot ×9 | Spinach ×9 | Chives ×16 | Radish ×16 |
Note what is absent: no beans or peas anywhere, because the allium block occupies four squares. If you want legumes, drop the onions and chives and put bush beans in the south rows instead — that single swap is the most common red-dot fix there is.
Related reading
- The complete companion planting guide — full chart with the reasoning
- Square foot gardening app — the grid the dots sit on
- Raised bed planner — planning several beds at once
Catch the bad pairings before they're in the ground.
Green dots and red dots, right on the grid. Free on iPhone.
Questions gardeners ask
Does companion planting actually work?
Some of it is well evidenced and some is folklore. The mechanisms with real support are physical: tall plants shading heat-sensitive ones, strongly scented herbs masking the scent cues pests use to find a crop, flowers drawing in pollinators and predatory insects, and legumes fixing nitrogen for hungry neighbours. Claims that one plant improves another's flavour are largely untested. The avoid-pairings are on firmer ground, because they are usually competition for the same nutrients or a shared pest.
The evidence behind each pairingWhich vegetables should never be planted together?
The reliable ones to separate: onions and garlic away from beans and peas, since alliums inhibit the nitrogen-fixing bacteria on legume roots. Fennel away from almost everything, as it is allelopathic. Potatoes away from tomatoes, since both are nightshades sharing blight. Brassicas away from strawberries. In a square foot bed these matter more than in a row garden, because neighbours are a foot apart rather than a metre.
Full companion planting chartIs Niwa free to use?
Yes. Niwa is free to download from the App Store, and the core planner — the garden grid, the plant library and the planting calendar — works without paying. Optional in-app purchases unlock additional features.
See it on the App StoreHow many plants fit in one square foot?
It depends on the crop's spacing requirement. A plant needing 3 inches fits 16 per square foot, 4 inches fits 9, 6 inches fits 4, and 12 inches fits 1. Large plants such as vining tomatoes or zucchini need more than one square each. Niwa works this out for you and prints the count straight onto the grid cell.
Plants per square foot calculatorCan Niwa plan a raised bed of any size?
Yes. You set the bed dimensions — 4×4, 4×8, 2×8 or a custom size — and Niwa draws the square foot grid to match. You can keep several beds and several gardens in the app at once and switch between them.
Raised bed plannerHow does Niwa know when I should plant?
Niwa uses your location to find your average last spring frost and first autumn frost, then works backwards from those dates for every crop in your bed. Each plant gets its own sow-indoors, transplant and harvest window on a month-by-month timeline, so the dates are yours rather than a generic zone table.
How the planting calendar worksDoes Niwa warn me about bad companion plants?
Yes. As you place plants on the grid, Niwa puts a green dot between neighbouring squares that benefit each other and a red dot between squares that are better kept apart, so you see the conflict while you are still planning.
Companion planting in NiwaHow much soil do I need to fill a raised bed?
Multiply length × width × depth in feet to get cubic feet, then divide by 27 for cubic yards. A 4×8 bed at 12 inches deep needs 32 cubic feet, roughly 1.2 cubic yards or sixteen 2-cubic-foot bags.
Raised bed soil calculatorDoes Niwa work offline, and do I need an account?
The whole plant library and all your layouts are stored on the device, so the app works with no signal — useful on an allotment. There is no account to create and your garden data is never uploaded to a server.
See what's includedWhich growing zones and countries does Niwa support?
Niwa works worldwide. It recognises USDA hardiness zones in the United States and derives frost dates from your location elsewhere, including the UK, Canada, Australia and Europe.
Find your frost dates and zoneHow is Niwa different from other garden planner apps?
Three things: it is a native iPhone app rather than a desktop planner viewed in a mobile browser, it shows companion-planting conflicts on the grid as you place plants instead of in a separate chart, and it works fully offline with no account.
Compare Niwa with other plannersIs Niwa available on Android?
Not yet. Niwa is a native iPhone app and needs iOS 18.0 or later. An Android version is not currently available.
Read the gardening guides in the meantime