Across allotments and back gardens, a simple tactic is gaining ground: using nasturtiums as living decoys to pull sap-sucking pests away from prized crops. The method costs little, takes a single afternoon to set up, and promises calmer tomato beds through the peak of aphid season.
What gardeners are doing
The approach is straightforward. Sow nasturtiums (Tropaeolum majus) in bands around tomatoes, then let the peppery-scented leaves and showy flowers lure aphids to an easier meal. Instead of spraying, you steer the trouble elsewhere. Many home growers report that this trap-crop border noticeably cuts aphid pressure on tomatoes, often within a fortnight of the first flush of pests.
Turn nasturtiums into a living decoy: ring your tomatoes at 50 cm, then let the aphids gather where you can manage them.
How the decoy works
Aphids favour soft, fast-growing foliage rich in sap. Nasturtiums deliver that in abundance early in the season, and their aromatic chemistry appears to broadcast a stronger signal than tomato foliage. By offering a tastier host a short step away, you break the direct pipeline from aphid flight to tomato stem. Beneficial predators follow the swarm to the nasturtiums, where control becomes easier and more visible.
What you need
- Nasturtium seed: 20–30 seeds per square metre for an effective edge
- Compost: 2 litres per square metre to enrich sowing rows (or a general-purpose potting mix)
- Watering can with a fine rose for gentle irrigation
- Hand hoe for shallow drills
- Organic mulch: straw or leafmould to steady soil moisture
Nasturtiums cope with poor to moderately rich ground. Too much feed drives rank growth and fewer flowers, and it also dulls their appeal as an aphid magnet.
Step-by-step set-up
Sow two weeks before planting tomatoes to establish the decoy while nights are still cool. Use this simple schedule.
| Task | When | Measurements |
|---|---|---|
| Prepare site | Early to mid-April (region dependent) | Lightly fork, add 2 L compost per m² |
| Sow nasturtiums | April to May | Drills 2 cm deep, 30 cm apart, seeds every 15 cm |
| Water to germinate | Daily for 10 days | Gentle spray until evenly moist |
| Set tomatoes | When frost risk passes | Plant tomatoes 50 cm from nasturtium line |
Care through the season
Germination takes 7–14 days depending on temperature. Once the nasturtiums leaf up, spread a thin mulch to reduce splash and keep moisture steady. Water the tomatoes deeply and the nasturtiums lightly so the decoy stays soft but not lush.
Expert touches that lift results
Pinch the aphid-heavy tips on nasturtiums but do not strip them bare; you want a steady magnet, not a clean sweep.
- Pinching strategy: Remove only the worst clusters every few days to prevent a boom-and-bust cycle.
- Feed balance: Keep fertiliser on the tomato root zone and away from the nasturtiums to maintain contrast.
- Predator support: Add a small insectary patch with dill, coriander and alyssum to feed hoverflies and lacewings.
- Ant patrols: Disrupt ant trails on the decoy plants, as ants farm aphids and protect them from predators.
- Airflow: Train tomatoes up supports and thin the nasturtium foliage near the soil line to reduce damp microclimates.
What results to expect
From June, many growers see the nasturtiums carry the bulk of the aphid load while tomato stems and flower trusses stay clean. Reports from small garden trials indicate a 70–80% reduction in aphids on tomatoes when the decoy ring is established and maintained. The effect depends on weather, local pest pressure, and whether predators settle in. Flowers are edible and add a peppery note to salads, so you gain more than pest management from the border.
Typical timeframe: visible diversion in 10–14 days after the first aphid flights, with peak benefit in late spring and early summer.
What could go wrong
Runaway aphid numbers on the decoy can spill pressure back onto crops. Keep to light, regular pinching and encourage predators. Watch for ants moving aphids to higher growth and break those routes. In a cool, wet spell, dense nasturtium foliage may trap moisture; open the canopy with a few cuts to improve airflow.
Chemical-free backups that pair well
Trap-cropping can sit alongside a few gentle tactics. A midday blast of water knocks aphids off tender tips without harming predators. Interplant with chives or garlic chives to add a light deterrent note around stems. Yellow sticky cards placed away from tomatoes intercept winged aphids before they settle, while keeping traps well clear of predator hotspots.
How to check you are near the 75% mark
Count to verify impact. Select five tomato plants at random. On each, choose two young leaves and two mature leaves. Count aphids on the undersides. Do this once before the nasturtiums start to draw pests and again two weeks later. A drop from, say, 20 average aphids per leaf to 5 puts you at 75% reduction. Keep notes, because consistent counts across different weeks tell you when to pinch nasturtium tips or add predator plants.
Numbers that help you plan
- Seed cost: a packet of nasturtium seed often sits near £2 and covers a small bed edge.
- Spacing: 15 cm between seeds gives a continuous, low wall of foliage for aphids to choose.
- Distance: 50 cm from tomatoes reduces root competition while keeping the lure in range.
- Resowing: new sowings each spring keep the decoy vigorous and predictable.
Beyond tomatoes: where the trick travels
The same decoy ring can shield beans, cucumbers and brassicas when early colonies build. Adjust placement so the nasturtiums sit just upwind of the crop’s prevailing breeze. In containers, sow a nasturtium in the outer rim of a large pot and support the main crop centrally; the principle holds on balconies as well as beds.
Extra tips for a stronger garden system
Think of the nasturtium border as a keystone in a wider plan. Add a shallow water dish with pebbles for beneficial insects. Leave a few self-sown nasturtiums where they do not crowd crops; volunteers often flower earlier and improve the early-season pull on aphids. Rotate the decoy edge each year to freshen soil and avoid a buildup of pest eggs in one strip.
If you like to model outcomes, assume a typical early-summer infestation would cut tomato truss set by 30%. Diverting three-quarters of the aphids can recover much of that loss. On ten plants, that may mean an extra kilo or two of fruit over the season, which more than pays for seed, compost, and a bit of time with the watering can.
Tried nasturtiums as a trap last year—saw fewer aphids within about two weeks. For £2 seed, it’s definitly worth a go this spring.