The Royal Horticultural Society Award of Garden Merit (RHS AGM)

Learned members of the RHS form a committee to assess the relative merits of specific plants within a family. They grow some of their own in extensive trials, visit specialist growers and then debate the various merits of a particular plant. For example, after deciding to assess perennial sweet peas they will form a group of members interested in sweet peas, grow a wide range of varieties in extensive trials, visit specialist collections and nurseries and then have a round table discussion to decide which particular sweet pea should get an award.

The criteria they look for are:

• It must be of outstanding excellence for ordinary garden decoration or use
• It must be available
• It must be of good constitution
• It must not require highly specialist growing conditions or care
• It must not be particularly susceptible to any pest or disease
• It must not be subject to an unreasonable degree of reversion in its vegetative or floral characteristics

So a plant may be truly outstanding in every area, but be too rare to be awarded a medal.

Fleuroselect

Founded in 1970, Fleuroselect is an association of flower seed breeders and trading companies. There are 23 trial grounds throughout Europe.

It recognizes its breeders in three ways:

• Gold Medal: awarded to varieties with the highest points in the trial. It is given for exceptional work on new colors, longer flowering periods, more uniformity, and disease resistance.
• Quality Mark: a certificate of merit for new flower varieties that are better than existing ones.
• Novelty Register: a register of new and distinct flower seed varieties. 

All American Selections

Very similar to the RHS AGM, but obviously awarded by judges in America to plants/varieties specifically suited to the USA. Though, due to the huge range of climates enjoyed in USA, this doesn't make it any less useful than the RHS awards.