For decades now, companion planting has been a popular choice among home gardeners seeking eco-friendly approaches to maximize their plants’ growth and vitality. Strategically pairing and planting two different plant species — roses and certain “onions,” in our case — results in a symbiotic relationship that helps create a beautifully nurtured, healthy ecosystem. For the rose bushes in your garden, you might consider planting them with onion relatives, like chives and alliums (aka ornamental onions), not only because of how well they complement roses aesthetically but because of the host of advantages these companion plants provide, including effective pest control.
(In)famous for their smell, members of the onion family do a fine job of confusing bloom-munching bugs like aphids and black flies by masking the rose’s smell. This helps drive them away without you having to resort to pesticides or chemical treatments. Such harmonious plant-pairing also benefits from improved soil fertility, as the onion bulb forages around for the deepest nutrients through an extensive root system and makes them available to the surrounding flora.
Guards against pests and diseases
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While green enthusiasts are pretty spoiled for choice, an onion best complements a rose as a companion plant when viewed from the perspective of preventing pest attacks. Like common onions, ornamental varieties like alliums contain several sulfurous compounds that lend them a sharp smell that insects find repulsive. Known to feed on rose foliage, invasive pests, such as borers, moles, weevils, slugs, beetles, cabbage worms, and aphids, steer clear of landscapes upon encountering these bulbous plants and their characteristic aroma. To get the best results, grow alliums and/or chives (Allium schoenoprasum) around your rose plants like a protective border or intersperse them; this will also strengthen your rose’s aroma.
Moreover, armed with their anti-fungal properties, members of the onion family minimize the likelihood of your garden queens contracting diseases like powdery mildew and black spot that result in discolored foliage. The presence of allicin in onions suppresses fungal action, lending natural protection to your botanical beauties. Allium bulbs also prevent the formation of gray mold, or Botrytis blight, on rose buds growing in humid conditions.
Improves soil condition
Beyond their protective attributes, flowering onions also play a crucial role in enhancing soil fertility. They’re adept at creating water channels through their deeply rooted fibrous system, which improves soil drainage and prevents waterlogging. They also maintain a harmonious nutrient profile by bringing forth essential elements, including nitrogen, phosphorus, potassium, and other trace minerals, from the medium’s entrenched layers. The surrounding rose plants benefit from this nutrient accumulation, to successfully grow robust blooms. Note that chives enjoy similar conditions, including full sun and well-drained soil, but the herb doesn’t require a lot of nutrients to thrive, so it won’t compete with roses for them.
Additionally, allium bulbs can assist your rosaceous gems in dealing with weeds that inhibit plant growth by limiting access to sunlight, water, and minerals. As onion plants possess dense foliage and extensive roots, they naturally restrict invasive growth, enabling roses to maintain their vitality and stave off weeds. However, when it comes to allium foliage — especially giant alliums — make sure the plant’s foliage remains masked from sunlight when planting them in your rosy flower bed to prevent them from turning brown and spoiling your garden’s look.
