Answer: If the planting area is only 4' wide, you might want to consider some of the tall-growing hedges instead of trees. Glossy Abelia, Boxwood, Calistemon (Bottlebrush), or Escallonia would serve the purpose and give some seasonal color as well. Fast-growing trees can have weak limb and branch structure, and can have invasive root systems, too, so are not always a good choice, even for young landscape situations. When purchasing plants, choose the largest size you can afford. Plants in one-gallon pots are the least expensive, but take the longest time to mature. Plants in five-gallon containers are generally 3-4 years old (depending upon rate of growth), and are more expensive.
Best wishes with your landscape.
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