Spruce (Picea) vs. Fir (Abies) -- how to tell the difference
    Spruce cones hang down, needles are stiff, sharp, square        Fir cones stand up, needles are soft, flat, flexible
great info from New Hampshire Garden Solutions

Dahlia Care Over Winter
How to find the eye (wait until spring, eyes will start to swell)

How to determine male or female holly plants by flower
              Male flowers have distinct short stamens                   Female flowers have a green swelling (or red) in the center

A really extensive comparison of caryopteris cultivars  

How to tell male and female flowers on persimmon
Female flowers are single and larger                                    Male flowers are in clusters and smaller

Evaluation of the best coneflower cultivars  
Echinacea comparisons

Weed ID post - good resource  
New York City Garden common weeds

Article on ninebarks susceptible to powdery mildew
Comparison of cultivars