• Hardy annual flowers can be grown almost anywhere.Design Pics/Valueline/Getty Images
  
  In many areas of the United States, both drought and cold can be a problem for gardeners who want to grow annual flowers. Fortunately, there are a number of hardy annuals that can grow and thrive in spite of adverse climate conditions. These flowers die off every year but will grow again from seeds or from their roots, providing color year after year with minimal effort.
  
  

Lantana

• There are many different species of lantana. According to the Brooklyn Botanic Garden, all of the lantana species are resistant to drought and other problems. Lantanas comes in many colors, including yellow, orange, red, lavender and white. One of the more striking varieties is the upright lantana, Lantana camara. In warmer climates, this plant does not die back in the winter and grows into a shrub; in colder zones the plant grows as an annual. In Hawaii and Florida, Lantana camara will become invasive and crowd out native plants, so it should be avoided by gardeners in those states. The weeping lantana, Lantana montevidensis, grows well in hanging baskets.
  
  

Moss Rose

• The moss rose (Portulaca grandiflora) is an annual that reseeds itself every year, germinating in the spring when the ground warms. It thrives in full sun and is extremely resistant to drought. The moss rose stands about 8 inches tall, with pink, yellow, white or orange flowers that look like small double roses. If seeds are scattered along walkways and driveways, the moss rose will take root and spread, crowding out more weeds each year as it pokes out between gravel and through the cracks in paving stones.
  
  

Yellow Cosmos

• Cosmos is a very hardy annual that is grown in many parts of the United States. One of the more widely cultivated types is the yellow cosmos (Cosmos sulphureus), which is highly tolerant of dry conditions and is a common site in such states as Texas and Arizona. Wild yellow cosmos can grow as tall as 4 to 7 feet, but cultivated varieties do not normally reach these heights.
  
  The center of the flower is usually bright yellow and the outer petals range from pale yellow to a rich orange-red. Recently, another variety appeared featuring vivid red flowers. Yellow cosmos requires full sun and will grow in poor soil conditions. If the soil is rich, the plant may grow too tall and become lanky. It starts easily from seed but must be planted in well-drained soil in order to thrive. For best results, water the cosmos only when the foliage begins to wilt, as too much water will cause the plant to become spindly.