Spring is the perfect time to start preparing the soil for new rose gardens and amending existing rose beds. Unlike many other perennial flowers, roses have very particular needs and require special preparation, but the reward of show-stopping blooms on healthy plants makes a little extra preparation worth the effort. The particular balance of inorganic and organic material needed for awesome roses is known as "loam." Loam consists of 50 percent pore space---room for air and water---and the other 50 percent a higher mixture of inorganic and lower amount of organic materials. The inorganic material needs to be 3 parts sand to 1 part sediment to 1 part clay.
Preparing Your Space
First, you need to know what your soil has an abundance of and what it's lacking. Cut straight down into your soil, digging up about an inch or two section and package it for testing. Avoid areas near compost bins or even dropped rotten plant waste as this will reflect a different pH balance than the rest of your space. Most full-service garden centers and your local agricultural council office should be able to test the sample for you for free. The test will help you correct the pH balance---or acidic levels---in your garden to give it the right balance as well as help you determine how much sand or sediment needs to be added.
Mix in added inorganic ingredients as specified by your testing results. Most garden soil contains enough clay, so you'll likely need to add some more sand or sediment---rich dirt. Take caution not to add too much sand to heavy clay areas. Sand will settle on top of the clay layer and trap water which can rot roots.
Roses need a low-acidic growing medium. Based on your pH results, you may need to add lime, a pulverized form of limestone, to the mix to counter a high acidic level. Do not over-mulch roses as too much organic matter will disrupt the pH balance needed.
Once your soil is complete, check the water drainage. To do so, dig a hole and fill it with water. If it drains within 15 minutes, your roses should do great.