Companion planting is the organic practice of pairing certain plants together to deter pests and to attract beneficial insects. You can use companion planting to help deter pests from your roses and from you potato plants. Other plants may aid in their growth by attracting certain beneficial insects or by fixing certain nutrients in the soil.
The fungal disease known as blackspot can damage your roses. To prevent blackspot, plant tomatoes, chives or garlic in your rose beds. Plant the garlic bulbs or chives approximately 6 inches from the base of each rose plant, and plant tomatoes at least 18 inches away. The chives and garlic also will keep white fly and aphids from feasting on your flowers.
Marigolds are also beneficial to your roses. They not only deter pests, but they also add nutrients to the soil that help rose plants to grow and bloom.
Marigold deter nematodes that can damage the roots of the potato plant, making the potato inedible.
Bush beans, carrots, celery and corn are also compatible with the potato plant. With their differing nutritional requirements they aid each other in sustaining growth. Horseradish is also beneficial to the potato plant. It encourages growth and deters the Colorado beetle and the blister beetle, both of which will chew on the potato plant root.
Herbs can be used throughout the garden, for both rose plants and potato plants, to help keep pests at bay.
Mint, marjoram, thyme and rosemary are all good perennial herbs that can help keep pests from your garden. Rosemary can be especially helpful as it often plays host to ladybug egg nests. Ladybugs feast on aphids and other small pests that can invade your garden.
Nasturtium is also helpful for your potato plants, and can compliment your rose garden. This flowering herb attracts the beneficial bugs such as wasps that will eat such pests as whitefly and aphids, both of which can harm your potato plants and roses.