Plants, like people, are searching for partners that will make them look good, bring out their best qualities and share their space with equanimity — neither overpowering nor paling in comparison.
There are several considerations when choosing suitable plant companions: aesthetics, growing conditions, and plant health. Plant companions should both look good together and require similar growing conditions. Another component of companion planting, one often referred to in organic gardening, is selecting companions that ward off pests, improve the soil or in other ways have a beneficial effect on plant health.
Texture, color, and form are all important in the aesthetics of companion planting. Plants with tall spires complement the wide, cup-shaped flowers of roses, while perennials and shrubs with pale green, silver or purple leaves accentuate the sumptuous rose blossoms. Companion planting can also extend the flowering season by providing color between the main flushes of rose bloom in early summer and fall.
Some plants just seem to be made for each other. The feathery purple and blue-gray catmint (Nepeta) offsets any pale pink rose beautifully, and its wispy spires gracefully camouflage any blemishes that may occur on the rose’s foliage. While the tops of roses are nice and lush, the bottoms can become leggy and sparse. Good companions are those that hide their bare legs. Traditionally, lavender (Lavandula), catmint (Nepeta), lady’s mantle (Alchemilla) and tall growing pinks (Dianthus) all make good partners. Good companions also act as living mulches—suppressing weeds and lightly shading the soil, keeping their roots nice and cool.
Good companions should enjoy the same growing conditions but not compete too aggressively with the roses. Roses do best in full sun and well-drained soil, and so should their companions. Plants that are too aggressive may crowd the roses and take too much water and nutrients from the soil.
Many sun-loving annuals such as heliotropes (Heliotropium), summer-snapdragon (Angelonia), lantana (Lantana), and verbena (Verbena) hold up well throughout the summer and fill the space among roses nicely. They all have modest water requirements and will benefit from the heavy feeding regime that roses demand.
Good companions are said to enhance one another’s growth or, in some way, protect each other from harm. Some companion plants may help discourage pests without the use of chemicals since there are natural substances in their leaves, flowers or roots that repel insects. Roses love garlic is a popular expression. In fact, members of the onion family such as chives, ornamental alliums and edible onions are rumored to increase the perfume of roses, ward off aphids and prevent black spot.
Herbs and other aromatic plants make wonderful rose companions. Scented geraniums (Pelargonium), rue (Ruta), feverfew (Tanacetum), parsley (Petroselinum), and thyme (Thymus) all may help ward off Japanese beetles and aphids. Marigolds (Tagetes) may also repel pests and encourage growth. Try ornamental and culinary sage (Salvia), anise-hyssop (Agastache), Russian-sage (Perovskia), lavender (Lavandula), yarrow (Achillea), oregano (Origanum), catmint (Nepeta) and calamint (Calamintha). Oddly enough, tomatoes allegedly prevent black spot, but not many people will be inclined to combine roses and tomatoes. Lavender (Lavandula) and catmint (Nepeta) are good at keeping rabbits away. Four-o’clocks (Mirabilis) and larkspur (Consolida) are said to act as decoys by attracting rose-loving Japanese beetles to eat their poisonous leaves. Yarrow (Achillea) may attract ladybugs who in turn feed on aphids.
Remember to plant companions at least one foot away from your roses so that you do not disturb their roots. Create a healthy open structure for your roses with good pruning practices. Always maintain good air circulation around your plants to help prevent attacks from pests and diseases. With proper care of your roses, you will be able to surround them with many interesting companions. Here a just a few suggestions:
Armitage's Garden Perennials by 
Easy Roses for North American Gardens by 
Landscape with Roses by 
Roses in Modern Gardens by 
The American Rose Society Encyclopedia of Roses by 
The Perennial Gardener's Design Primer by 
The Well-Designed Mixed Garden by 
