Roots

• Drought causes low soil moisture, which can result in root damage. Nearly 99 percent of root mass resides in the top three feet of soil. The feeder roots and root hairs that take up water and nutrients inhabit the top 12 inches of the soil, and they are the part of the root system affected by drought. Symptoms of root damage in shrubs include: canopy thinning, slow growth, and stunting.
  
  

Weakened Defenses

• Drought also weakens a shrub's defenses leaving it more open to insects and disease. Drought-affected shrubs are more likely to develop fungal tip blights, vascular wilts, root rots and needlecasts.
  
  

Sensitive shrubbery

• Drought induced plant stress can also increase a shrub's sensitivity to air pollutants, as well as common household items such as de-icing salts and pesticides.
  
  

Planting issues

• Poor planting practices can enhance drought's affects. Choosing unfavorable sites, improper rootball preparation, planting too deep or shallow and over-mulching make it easier for drought to harm a shrub. Drought hits seedlings and new transplants hardest since transplants lose some feeder roots during transplant.
  
  

Preventative measures

• Help your shrubs become more drought hardy by:
  1) Watering them with one inch of water per week. Water after sunset with a slow, deep soaking to a depth of approximately 12 to 18 inches. Don't over water.
  2) Select the appropriate site for shrubs with regard to sunlight and soil.
  3) Select native plants or drought-tolerant shrubs.
  4) Mulch to maintain soil moisture, but don't use so much mulch that water travel to roots becomes blocked.
  5) Prune any dead or weak limbs.
  6) Generally, plants under stress shouldn't be fertilized, but applications of biostimulants, mycorrhizae, or similar compounds can help stimulate root growth and regeneration.