Too much or too little water:  Newly transplanted plants require a little extra watering while established plants require 1 inch of water per week to grow well.  Keep the plant's roots moist, not saturated, throughout the planting process.  Your soil and rainfall will determine how often to water.  Clay soils retain moisture while sandy soils drain quickly.  Before you water see if the soil is damp or dry about 4 inches deep which is about the length of your index finger.  An organic mulch will help retain moisture.  Too much water will reduce the amount of oxygen in the soil and will suffocate the plant. Watering deeply and thoroughly and only as needed will encourage a deep and healthy root system that can withstand drier times.

Planted incorrectly:  Digging a hole and plopping the plant into the hole seems simple enough, but much can go wrong during this important step.  A tree, shrub or flower planted incorrectly can end up with girdling roots which will ultimately lead to the slow death of the plant.  Dig the hole twice as wide as the root ball and about 1-2 inches less than the height of the root ball.  Root flares of trees should be above ground.  If sides of a tree go straight into the ground without a flare it is planted to deep.

Roughen the sides of the hole to help the roots penetrate through.  Check the root ball for any roots that are circling around it. Make 2 or 3 vertical cuts around the root ball or loosen the ball to avoid circular roots. (Do not disturb the root ball of a balled and burlap plant. Cut the circulating root.)  Backfill with original soil to avoid creating an interface of soils.  Plants will grow best in the original soil, particular if you are planting plants for your soil type.  If amending the soil is necessary, it is best to amend the entire planting bed versus individual holes. Or retain 2/3 of the original soil and add the other 1/3 with a soil amendment.  Roots are opportunistic and if they are in a highly nutrient rich soil they wouldn't grow beyond the originally dug hole.    

Construction Projects:  Home or landscape construction projects can cause havoc on existing trees if precautions are not taken.  Soil compaction from trucks, skid loaders, materials, and foot traffic reduces the amount of oxygen getting to the roots.  Construction spills and buried debris can impact the soil.  Changing the grade of soil, removing too much of the tree's root system or changing the environment can stress the tree and invite pests and diseases.  Work with the contractor to protect the trees roots which extend as much as 40' beyond the tree's canopy.

Check out local technical colleges with horticulture programs, garden clubs, and Master Gardener chapters to see if they hold annual plant sales.  Bargain prices for annuals and perennials can be found here. 

Dakota County Technical College's annual plant sale will be May 8 and 9 from 8 am to 2 pm.  Annuals, perennials, hanging baskets and container gardens are sold with proceeds going to the horticulture club.  Plants go quick so it's best to shop early.