While some cultivars of roses have varying shades of colour, rainbow roses provide a burst of vibrant colour in each blossom. Rainbow roses get their tie-died appearance from a colouring technique, not as part of their natural growth. Although rainbow roses do not achieve their multicoloured appearance naturally, you can grow suitable roses to use in creating your own rainbow roses.
Select rose cultivars with long stems, such as floribunda and hybrid tea roses. Choose ones that bloom in pale shades, such as white, cream or soft yellow. "Ivory Fashion" and "Nicole" are suitable floribunda cultivars, while "Crystalline and "Lynette" are hybrid tea roses that make attractive rainbow roses.
Prepare a site for your rose in a sunny area of your garden. Roses need at least six hours of sunlight to produce quality blossoms. Choose a location that provides some shade during the heat of the afternoon during hot summers.
Prepare the planting site by digging a hole that is about two to three times wider than your rose's roots. Place the rose plant into the hole, keeping the crown slightly above the surface of the surrounding soil. Mix equal amounts of potting compost with the backfill and place the soil around the root-ball, filling in the hole.
Water the rose plant immediately after planting to moisten the soil throughout the roots. Irrigate around the perimeter of the plant when the surface becomes dry, watering deeply enough to soak the soil throughout the root area. Depending on the porosity of your soil and rainfall in your area, you may need to water 2.5 to 5 cm every week or two. Apply a rose plant fertiliser ever four to six weeks during the spring and summer months.
Harvest rose blossoms when the buds start to open. Use a sharp knife, rather than pruning shears to cleanly cut the rose stem where it connects to the main plant. This will provide the length necessary for the dying process. Slice the bottom 10 to 15 cm of the stem lengthwise to form four long sections.
Pour 5 cm of water into the bottoms of four narrow glasses. Place 15 to 20 drops of food colouring in the glasses, using a different colour for each one. Place the vases against each other, bringing all four into a circle. Place a rubber band around the narrow vases to hold them tightly together. Insert your rose into the vases, placing a section of the stem in each vase.
Place the rose in a cool, shaded location while it absorbs the colour into its stem and petals. Once the rainbow rose reaches the desired level of colour, remove it from the four vases and place it in a single vase of clear water and display in your desired location.