Meadow and layered podzol (gray forest) soils occur in most of the higher elevations throughout the country. Intermediate elevations usually have brown forest soils, some of which are excellent. The Maritsa and Tundzha and the major rivers that flow into the Danube have wide valleys with alluvial soils. They may be coarse, but most of them are fertile, drain well, and are extensively cultivated.
Both the natural vegetation and the cultivated crops that have replaced it on all areas that could be put to agricultural use reflect the transitional climate of the country. North of the Stara Planina the original flora was a continuation of that on the Russian steppe. The steppe influence was greatest in the east, giving way to deciduous forests farther to the west.
Lands south of the mountains, sheltered from the colder extremes of the continental weather systems, have been able to support plant life that could not exist on the steppe. Areas along the Black Sea coast and in valleys of the Rodopi that open to the south experience further moderation. Many Mediterranean and subtropical species have existed in them naturally, and others introduced by man have thrived.
What remains of the original vegetation on the Danubian plateau is found mainly along the river, where the land has been difficult to cultivate. It includes brush grass, reeds, and licorice. The last two have commercial value. Most of the original lowland deciduous forests have been removed, and grain flourishes on the level expanses where the soils are favorable. Other food and fodder crops are grown to satisfy local requirements. The foothills of the Stara Planina are dotted with orchards; plums are the most prevalent fruit in these northern areas.
The depression, or geological trench, between the Stara Planina and the Sredna Gora ranges, which is at the near center point of the country and contains the upper valleys of the Tundzha, Stryama, and Topolnitsa rivers, is sheltered and very humid and is ideal for the raising of roses. One in particular, Rosa Alba, has become known as Bulgaria's gold. Its flower is not an especially lovely variety, but it is extremely rich in the rose oil that is the basic fragrance in many perfumes and a flavor in certain liqueurs. Fields of them flourish in the Kazanluk area, the so-called Valley of Roses.