Plant Material - Project Planning and Management for Ecological Restoration - page 116

embryos are present in seed that takes several years to finally germinate. Seeds have a dormancy
period, which for some species can be several years. Germination testing is not practical in these
situations. Also, some seeds have a hard coat that can take years to deteriorate. In addition, some
species require fairly elaborate or complicated treatments to cause germination, such as scarifica-
tion, cold storage, stratification, or fire treatment (Leck, Parker, and Simpson 1989). Other species
have a very short shelf life.
Certified seed sold in the United States must, by law, display the purity and germination per-
centage on the seed tag attached to the seed bag. As discussed earlier, more than just seed is in-
cluded in the bag. Many—but not all—seed providers supply a PLS (“pure live seed”) percentage
on the tag. Knowing the PLS of your seed lot is an important first step in developing a seed mix
that will provide the desired results.
Pure live seed is calculated by multiplying the purity and germination rates by the bulk quantity
of seed. Thus, with seed tags containing a purity rating and germination rate, you have the ability
to determine the weight of live seed. Knowing the cost for a bulk pound, you can then determine
the per pound cost by using the formulas shown in box 8-1.

Box 8-1. Calculating Pure Live Seed and Cost
A seed test report includes the following:
Pure Seed 73 percent
Inert Matter 4 percent
Other Crop 0 percent
Weed Seed 3 percent
Germination 47.31 percent
Dormant Seed 15.03 percent
Total Germination and Dormant Seed 62.34 percent
(some use the phrase “viable seed” for this total)

PLS = purity % × total germination % expressed as decimals (to four places)
PLS = 73% × 62.34% ÷ 100 = 45.51% PLS

For this seed lot, the PLS tells us that for every one bulk pound of live seed, only 45.51
percent is live seed. Or, if you bought 25 pounds bulk, in effect you would be getting
only 11.38 pounds of seed capable of producing plants on your project.

What would one pound of live seed cost?
The seller charges $5.75 per pound bulk seed for this species.
PLS cost per pound = bulk price ÷ %PLS

= $5.75 ÷ 45.51%

= $12.63 cost for one pound of PLS seed