Crabgrass Germination Fact Sheet

CRABGRASS GERMINATION FACT SHEET
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Many pasture grass seeds do not germinate and establish seedlings quickly or uniformly in the field. This behavior is common in native range grasses, Old World Bluestem, bermudagrass, bahiagrass, fescues, crabgrass, etc. This information is intended to illustrate the above characteristic in crabgrass, including Red River crabgrass. This characteristic is incredibly variable and dynamic. Some seed lots do germinate early and at an excellent level. Others germinate at a low level soon after harvest and at a high level a few weeks later or a year later. However, the general behavior is that fresh seeds of the latest harvest of crabgrass, properly planted, begin germination when soil temperature and moisture are suitable. That germination continues, more or less, after each rain until the stand is full or the season is done. This may be quick or it may go on for several months. It is wise not to be impatient. Some stands emerge immediately. All we managers can really do is: Plant the seed properly and care for the planting properly. Plant aged seed; i.e., when it is available, choose aged seed (1 year old, more or less) over fresh seed. Some producers secure seed a season before they need it and let it "age" and break more dormancy prior to the time of actual planting the next season.

Some producers purposely plant seed long before it can germinate in the warm weather of spring and summer with part of the idea being that exposure to the elements will hasten dormancy breaking and cause quicker germination when the temperature gets warm. Overseeding in wheat is an example of this. However, the effectiveness of this has not been demonstrated in controlled studies for crabgrass, but it is known to be correct for some other grass seeds.

To illustrate some seed germination and dormancy characteristics of crabgrass the following data is presented from 5 years of our results. The data is only from seed lots that had a "low" germination during fall of the year of harvest. It does not include data from seed lots that germinated high (usually over 80%) during the fall of the year of harvest.

Seed Germination and Dormant Seed Test Results of Crabgrass Seed.

Fall of Harvest Year

Spring Following Year of Harvest

Item	Germination	Dormant Seed	Inert Seed	Germination	Dormant Seed	Inert Seed	Relative % Increase In Germination By Spring
Average	61	18	21	85	3	12	40%
Low Range	1	1	---	78	0	---	7700%
High Range	82	92	---	95	20	---	16%

The data illustrates many things when considering the major point of only germination. It is shown that aging the seed from fall to spring, averaged increasing germination a relative 40% over the fall tests. At the low range, there was an incredible change from 1% germination in fall to 78% in spring. Even at the high range, germination increased a relative 16% from fall to spring. This information should help managers to interpret test results and the phenomenon of germination characteristics as well as field germination and stand emergence characteristics.

It is important to know what % PLS is and how it works in a planting environment. % Pure live seed (PLS) is the % of good seed, i.e., it is viable (live) and is expected to germinate. When a full pound of PLS seed is planted, a full pound of "good" seed is planted without consideration for the inert and non-good seed. When planting a pound of PLS/ac we should also consider how much of that pound is germinatable in tests and what is dormant and should germinate later. For example, if a lot is 94% pure seed, 78% germination and 11% dormant seed (89% live seed) the % PLS is 83% [(94% x 89%)/100]. 8% (100%-92%) of the seed batch is inert matter in some form (chaff, leaf dust, stem parts, etc.) To plant one pound of PLS this seed would require 1.2 lbs. of total seed [(1/83) x 100]. For each pound of PLS of this seed planted, 88% is germinatable seed [(78% / (78%+11%))x100].

When seed is planted by the lb. PLS it makes little difference what the % germination is, within reason, because seed is planted on the basis of good germinatable and dormant, but live seed, not just total net weight of seed. The seed user can apply these equations to any seed lot.