With seed trays filling and costs rising, a peppery annual is quietly changing how many households tackle spring aphids.
Across Britain’s allotments, patios and balconies, growers are turning to a Victorian trick with a modern name: trap cropping. By sowing nasturtiums as decoys near treasured tomatoes and brassicas, many report aphid numbers falling by roughly three-quarters, while pollinators keep visiting and salad bowls gain edible flowers.
What is happening in gardens now
As April warms, packets of nasturtium seed are moving from drawers to soil. Gardeners are sowing them two weeks before tomato planting, then setting tomatoes 50 centimetres away once the orange and red shields leaf up. The idea feels counterintuitive: invite pests to a plant you can spare so they ignore the one you cannot.
Plant nasturtiums a fortnight before tomatoes and keep 50 cm between species. Expect the first aphid shift within three weeks.
The approach revives an old practice once common in European cottage plots. Today it fits neatly with tighter budgets, shrinking pesticide shelves and a desire to keep bees, hoverflies and ladybirds safe.
How the trap works
Nasturtiums carry soft, succulent growth early in the season. Their leaves release peppery volatiles that aphids readily home in on. Once colonised, the plants hold sap-suckers in place, diverting attacks away from tomatoes and other tender crops nearby. The sticky honeydew they shed draws in ants, which further pen the aphids on the decoy, and the flowers continue to feed pollinators.
By June, many growers see nasturtiums thick with greenfly while tomatoes remain unblemished. Reports commonly describe a 70–80% decline in aphids on target crops when spacing and timing are right, with 75% a realistic figure in ordinary back gardens.
The steps at a glance
Timing: sow nasturtiums outdoors between April and May, around two weeks before transplanting tomatoes.
Depth and spacing: place seed 2 cm deep, every 15 cm along rows 30 cm apart.
Watering: use a fine rose, keep the topsoil evenly moist for 7–14 days until germination.
Placement: set tomato plants about 50 cm from established nasturtiums to avoid root competition yet keep the lure close.
Maintenance: pinch back tips on aphid-laden nasturtiums to slow runaway growth while preserving the live decoy.
Refresh: resow nasturtiums each spring to maintain strong attraction and tidy plants.
Materials you actually need
Nasturtium seed: 20–30 seeds per square metre of bed.
Compost: roughly 2 litres per square metre for sowing pockets, or a light sprinkle of general-purpose potting mix.
Watering can with a fine rose for gentle seedlings.
Hand hoe or small mattock to draw shallow furrows.
Organic mulch such as straw or leafmould to stabilise moisture once plants establish.
A thriving decoy keeps predators fed and pests busy elsewhere. Leave some aphids on the nasturtiums or the trap stops working.
Results: what gardeners report
Patterns are consistent. By early summer, nasturtiums carry the lion’s share of aphids. Tomatoes, set back a half-metre, push glossy foliage and set trusses with fewer curls, leaf puckers and honeydew speckles. Growers who follow the timetable and spacing commonly see three clear gains: fewer aphids where it counts, healthier tomato growth, and a bonus harvest of peppery petals and young leaves for salads.
Approach
Expected aphid reduction
Pollinator impact
Cost per season
Effort
Broad-spectrum spray
Rapid knockdown, short-lived; repeat often
High risk to non-target insects
Medium to high (repeat purchases)
Low per use; frequent reapplication
Nasturtium trap crop
About 70–80% on target plants when timed well
Low risk; flowers feed beneficials
Low (seed, compost, mulch)
Moderate: sow, pinch, monitor
Expert tweaks to boost impact
Go easy on fertiliser. Overfed nasturtiums throw lush, sprawling leaves that shadow crops and draw more sap than the root zone can supply. A lean, well-drained bed keeps plants attractive to aphids without overwhelming neighbours. Pinch soft tips where colonies cluster to check growth and confine the buffet.
Keep the trap active. If you wipe out every aphid on the nasturtiums, the pressure may bounce back to your tomatoes. Aim for containment, not eradication. When a plant becomes a heaving black mass, remove that single plant and drop a fresh seedling in its place.
Lean soil, bright light and regular pinching give you a compact lure that attracts pests yet stays manageable all season.
What could go wrong
Too many aphids on one plant can spill to crops during heatwaves, especially in still air. Space decoys so leaves do not touch tomatoes, and promote airflow. Ant activity around honeydew can protect aphids; use simple ant barriers on stakes or break nearby nests early in the season.
Virus transmission is a risk in any aphid year. Growing a few smaller nasturtium clumps around a bed, rather than a single dense hedge, reduces the chance of a short, direct hop from a heavily infected leaf to a tomato. Avoid overhead watering late in the day, which leaves sticky leaves overnight and favours sooty mould on honeydew.
Where this shines and where it doesn’t
Decoy planting suits container patios, raised beds and traditional rows. It excels alongside tomatoes, cucumbers and brassicas, where growers can keep a clean 50 cm gap and prune regularly. In cramped greenhouses, trial a single pot of nasturtiums near the door to draw early flights away from seedlings, then remove it once ladybirds arrive.
During severe infestations, combine the trap with gentle measures: a morning hose-down to dislodge colonies from nasturtiums, soft soap on decoys only, and releases of ladybirds or lacewing larvae if you use them. Aromatic herbs like rosemary and thyme can sit at the bed edges to provide nectar for predators and a light masking scent without clashing with the decoy’s pull.
Action plan for the next four weeks
Week 1: sow nasturtiums outdoors, 2 cm deep. Label rows, water with a fine rose, and mark tomato positions 50 cm away.
Week 2: thin seedlings if crowded. Lay a thin mulch to hold moisture. Prepare tomato planting holes with compost only where the tomatoes will sit.
Week 3: transplant tomatoes on a warm, still evening. Stake them immediately to keep foliage upright and separate from the decoy leaves.
Week 4: inspect nasturtiums every other day. Pinch soft tips with clusters, leave a steady aphid presence, and remove one overrun plant if needed.
Extra notes for keen growers
Choose compact nasturtium varieties near paths and trailing types to spill over bed edges. A mixed sowing gives continuous bloom and a more resilient decoy. Single-flowered forms often draw more insects than heavily doubled blooms. If you plan to eat flowers, pick from plants with light aphid pressure and rinse gently to remove honeydew.
Spacing and numbers matter. A practical ratio is one nasturtium for every two tomato plants, with decoys set slightly upwind of the crop if your plot has a prevailing breeze. Reflective mulches beneath tomatoes can further reduce landings by confusing flying aphids, while the nasturtiums offer a clear, attractive target nearby.
Think across the season. Resow a handful of nasturtium seeds in late May to replace any decoys that age or succumb to slugs. Keep notes on dates, distances and weather so you can tune the trap next year. Small adjustments—five centimetres closer, a pinch earlier, a lighter feed—often move results from good to striking.
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