Cost issues  

When soils or groundwater are contaminated, cleanup can be very expensive. Traditionally, contaminated soils are either:

 

excavated and buried as hazardous waste;

temporarily excavated, “washed,” and returned to the site;

treated with engineered microorganisms that break down organic contaminates (bioremediation), or;

capped with imported fill.

 
It is generally agreed that phytoremediation techniques can reduce costs anywhere from fifty to ninety-eight percent compared to traditional remediation. Phytoremediation is also less expensive than bioremediation, a technique itself considered to be cost-saving. Growing plants on site is several hundred times cheaper than growing an equivalent weight of bacterial biomass. Plants are easier to propagate and do not require sterile growing conditions, organic nutrients, or the laboratory facilities necessary for growing bioremediation microorganisms (aspb).  
An example of the kind of cost savings possible is discussed in the EPA Phytoremediation Handbook: The authors have estimated that the 30-year costs of remediating a 12-acre site contaminated with lead are as follows:  

$12,000,000 for excavation and disposal
$6,300,000 for soil washing
$600,000 for installing a soil cap
$200,000 for phytoremediation (installation and maintenance)

  
The cost savings are less dramatic, but still significant, in other remediation projects. When groundwater is contaminated, phytoremediation is estimated by GWRTAC to cost less than half what traditional “pump and treat” technologies do. Groundwater plumes controlled by the hydraulic action of fast-growing poplars are many times cheaper to install and maintain than a system of constructed dams, levees, and drainage pipes to control contamination of nearby groundwater.
  
The tradeoff, however, is in time and maintenance. While costs are lower overall, phytoremediation techniques are far from a “quick fix.” Plants— especially trees—take years to mature to their full remediating potential, and sites must be monitored and maintained for many years to ensure human and ecological safety. It is therefore imperative that a source for constant funding be secured in advance to ensure a complete and conscientious maintenance plan for the duration of the remediation project.