Chalk, or calcareous soil, is found over limestone beds and chalk deposits that are located deep underground. This type of soil is sticky and hard to work with when wet, and it can dry out very quickly in the summer. Chalk is also very alkaline, with a pH of 7.5 or more on average [source: BBC]. This high pH is caused by lack of moisture and high lime content, which can cause stunted growth in plants. Excess lime can also turn these plants yellow [source: Gardening Data].
To make chalk more plant-friendly, try adding acid-rich materials like peat, compost or manure. These materials will help to neutralize the soil and can eventually reduce lime content by improving water absorption. If you'd prefer to keep things simple, focus on plants that thrive in alkaline-based soils, including lilacs, lilies and many types of flowering shrubs. Avoid richly colored flowers like rhododendrons that need a more acidic environment [source: BBC].