What Not to Plant With Nasturtiums

Understanding Nasturtium Companionship

When considering what not to plant with nasturtiums, it's crucial to understand their role in the garden. Nasturtiums are celebrated for their dual purpose: they are edible, adding peppery leaves and flowers to salads, and they act as a trap crop for common pests like aphids, drawing them away from more vulnerable vegetables. However, this beneficial plant can be negatively impacted by certain neighbours, leading to reduced vigour, increased susceptibility to disease, or an influx of pests rather than their deterrence.

The goal of companion planting with nasturtiums is to create a harmonious ecosystem. This means selecting plants that either benefit from their presence, tolerate their growth habits, or are actively deterred by their natural compounds. Conversely, unsuitable companions might compete for resources, suppress growth through allelopathic effects, or attract the very pests that nasturtiums are meant to repel. Understanding these dynamics prevents common gardening frustrations and ensures your nasturtiums, and their neighbours, can thrive.

• Avoid planting brassicas close to nasturtiums.
• Fennel can inhibit the growth of many plants, including nasturtiums.
• Nasturtiums may not thrive when crowded by large, dense plants.
• Certain plants attract pests that can overwhelm nasturtiums.

The Nasturtium's Needs

Nasturtiums (Tropaeolum spp.) generally prefer well-drained soil, moderate moisture, and plenty of sunlight. They are not heavy feeders; too much nitrogen, often found in rich composts, can lead to lush foliage at the expense of flowers. They have a sprawling habit, meaning they can take up considerable space. Understanding these preferences helps identify potential conflicts with other garden inhabitants.

Plants to Avoid: The Problematic Pairings

When deciding what not to plant with nasturtiums, certain vegetable families and herbs immediately come to mind due to pest attraction or growth inhibition. The most frequently cited group to keep at a distance are the brassicas, which include cabbage, broccoli, Brussels sprouts, cauliflower, kale, and radishes. Nasturtiums are often planted to lure aphids away from brassicas, but placing them too close can mean the aphids simply transfer to the vulnerable brassica crop or that the brassicas, with their dense foliage, shade out the nasturtiums, preventing them from fulfilling their aphid-trapping role effectively.

Another plant to reconsider nearby is fennel. Fennel is known for its strong allelopathic properties, meaning it can release chemicals that inhibit the growth of many other plants. While it's beneficial for attracting hoverflies, its presence can suppress the vigour of nearby nasturtiums, leading to stunted growth and fewer blooms. Similarly, potatoes can be problematic. While not directly harmful, potatoes often require rich soil and consistent watering, which can lead to overly lush, less floriferous growth in nasturtiums if they are too close and benefit from the same nutrient-rich environment. Large, sprawling plants that demand significant space and nutrients, such as pumpkins or large squash varieties, can also overwhelm nasturtiums, shading them out and competing heavily for resources.

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Brassicas: A Case of Shared Pests

While nasturtiums are a known aphid trap for brassicas, this pairing works best when there is a physical distance between the two. If planted immediately adjacent, the aphids are likely to find the brassicas anyway, and the nasturtiums may become overwhelmed, compromising their health. Consider planting nasturtiums further away from your brassica patch, perhaps along a border or in a separate area, to draw aphids away from the entire vegetable bed.

Fennel's Inhibiting Influence

Fennel's potent allelopathic compounds can significantly impact the growth of many garden plants. It is generally advisable to plant fennel separately, away from plants like nasturtiums, beans, or tomatoes, which can be sensitive to its presence. This isolation allows fennel to attract beneficial insects without negatively affecting its neighbours.

Companion Planting Alternatives for Nasturtiums

Given the potential conflicts, it's helpful to know what to plant with nasturtiums to foster a healthy garden ecosystem. Many herbs and flowers complement nasturtiums wonderfully, offering mutual benefits or simply coexisting peacefully. For instance, planting nasturtiums near many fruit trees can help deter pests that might otherwise target the fruit. Marigolds are another excellent companion; their scent can deter nematodes in the soil and their bright flowers add visual appeal nearby.

Herbs such as rosemary, thyme, and sage are also good neighbours. These Mediterranean herbs thrive in similar well-drained conditions and their aromatic qualities can help deter certain pests. Growing cosmos in pots or in the ground nearby can add a splash of colour and attract pollinators without competing heavily. For those looking to extend their edible garden, planting radishes in the same bed but with adequate spacing can sometimes work, as the nasturtiums may lure flea beetles away from the radish leaves. However, extreme caution is advised with brassicas, as noted previously, and keeping them distant is the safest bet. Sunflowers, when planted at a reasonable distance, can provide a striking visual contrast and attract beneficial insects.

Plant dill or mint in pots next to your nasturtiums. These herbs are excellent aphid deterrents and attract beneficial insects, but their vigorous root systems can take over garden beds, so containerising them prevents them from outcompeting your nasturtiums.

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Beneficial Flowering Companions

Flowers like calendula, zinnias, and petunias are generally good companions for nasturtiums. They attract pollinators and beneficial insects, and their varied growth habits mean they are unlikely to compete aggressively for light or nutrients. Zinnias, in particular, are known to attract pollinators, contributing to a vibrant garden environment.

Herbal Allies

Many common culinary herbs offer more than just flavour. Planting aromatic herbs like basil, oregano, and chives alongside nasturtiums can help deter common garden pests with their strong scents. Remember that while these herbs are generally good companions, ensuring adequate spacing prevents dense overcrowding.

Optimising Placement and Care for Nasturtiums

Beyond selecting the right companions, the physical placement of your nasturtiums significantly influences their success and their ability to deter pests. Nasturtiums thrive in full sun but can tolerate partial shade, especially in hotter climates where a little afternoon shade can prevent scorching. However, overly shady conditions will reduce flowering and make them more susceptible to fungal diseases. Therefore, avoid planting them in perpetual shade cast by large trees or buildings.

Soil is another critical factor. While nasturtiums are forgiving, they perform best in moderately fertile, well-drained soil. Overly rich soil, particularly high in nitrogen, will promote rampant leaf growth at the expense of flowers and can make the plant more attractive to aphids. This is why planting them amongst heavy feeders or in areas heavily amended with compost might not yield the desired results. When planting, ensure there is sufficient space for their trailing or bushy habit to develop without immediately encroaching on or being engulfed by neighbours.

Spacing is Key

Give your nasturtiums room to grow. Depending on the variety, they can spread from 30cm to over a metre. Adequate spacing prevents competition for light, water, and nutrients, and also ensures good air circulation, which is vital for preventing fungal issues.

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Watering Wisely

Water nasturtiums regularly, especially when they are young and during dry spells, but allow the soil to dry slightly between waterings. Avoid waterlogged conditions, which can lead to root rot. Overwatering, particularly in conjunction with rich soil, can encourage aphid infestations.

The right companion planting strategy for nasturtiums is about balance – attracting beneficials, deterring pests, and avoiding competition.

Recognising and Preventing Nasturtium Problems

Even with careful planning, problems can arise. The most common issue with nasturtiums is aphid infestation, which they often attract intentionally as a trap crop. If you notice a large build-up of aphids on your nasturtiums, it means they are doing their job. You can often wash them off with a strong jet of water, or introduce beneficial insects like ladybirds and lacewings, which are natural predators. If the infestation is severe and spreading to other plants, you might need to remove heavily infested parts of the plant or consider a mild organic insecticidal soap, though this should be a last resort.

Another problem can be powdery mildew, especially in humid conditions or when plants are overcrowded and lack good air circulation. Ensuring proper spacing and avoiding overhead watering, particularly in the evening, can help prevent this fungal disease. Leaf spot is another possibility, often appearing as dark spots on the foliage. Good garden hygiene, such as removing fallen leaves and diseased plant material, is crucial for prevention. If companion planting is done incorrectly, you might see reduced flowering or stunted growth, signals that the surrounding plants are either too competitive or are negatively affecting the nasturtiums.

Inspect your nasturtiums regularly for pests and diseases. Early detection is vital; a quick spray of water can dislodge aphids before they become a major problem, and prompt removal of affected leaves can stop mildew spreading.

When Nasturtiums Aren't Blooming

If your nasturtiums are producing masses of leaves but few flowers, the most common cause is too much nitrogen in the soil. This often happens when they are planted in overly enriched beds or too close to plants that require heavy feeding. Reducing fertiliser application and ensuring they receive adequate sunlight will encourage more blooms. Conversely, if they are in very poor soil, they might not have the energy to flower; a light dressing of a balanced, low-nitrogen fertiliser can help.

Dealing with Pests

While nasturtiums are known for pest deterrence and trap-cropping, they are not immune. The key is understanding that their own infestation is often a sign they are protecting other plants. Management should focus on supporting the nasturtiums and their role, rather than eradicating the pests from them entirely, unless they pose a threat to adjacent, more valuable crops.