Hi Lisa, 

There are many reasons why a garden can underperform - great instinct to check the soil, as this would be one of the first questions I would have as well!

UVM Extension provides soil testing to consumers. Below you will find a link to the general page for UVM soil testing for home and commercial soil:

Agricultural and Environmental Testing Lab | UVM Extension Cultivating Healthy Communities | The University of Vermont

This covers the basic FAQ's and information about getting testing done. 

Recommendation is that, if you have multiple distinct gardens you are curious about,  you send one sample for each distinct planting area. Although test kits are available, it is often easier to fill a clean, plastic zip loc bag with about 1/2 to 1 cup of soil. One bag=one sample. 

Your shipment of sample (or samples) should be accompanied by a completed soil test submission form (Microsoft Word - Current Garden_hort_questionnaire.docx (uvm.edu)) and a check for the total cost as completed on the form. 

Soil tests/forms and payment should be mailed to: 

Univ. of Vermont, AETL, 262 Jeffords Hall, 63 Carrigan Drive, Burlington, VT 05405-1737

A basic test will cost you $17 per sample. 

Hope this helps!

Kristin