The length of time it takes weed seeds to germinate can vary considerably even within the same field due to variations in soil and microclimatic conditions. Every year can be different. We conducted a test to determine how long it took for various weed seeds to germinate after they were exposed to moisture. Seven summer and winter annual weeds, two grasses and five broadleaf weeds were chosen for this test. Seeds for these weeds were placed in teabags and buried ¼ inch below the soil surface and in the seed row of newly planted lettuce fields prior to the germination irrigation. Teabags were pulled every 24 hours and evaluated for germination. This procedure was repeated in both sprinkler and furrow irrigated fields at 8 locations at Roll, Bard, The Gila Valley, and the Yuma Valley. The tests began in August and were conducted each month until February. The time to germination appears in the following table. The time to germination for the summer annual grass (barnyardgrass) was 24 hours in august and September, became longer in October (48 hours) and still longer in December (96 hours). It did not germinate in January. The winter annual grass (cannarygrass) took 168 hours to germinate in September and dropped to 96 hours in December. The summer annual broadleaves took from 24 hours (Purslane) to 96 hours (Pigweed and Nightshade) to germinate. The winter annual broadleaf weeds (lambsquarters and Shepardspurse) took from 72 to 168 hours to germinate.

Hours to Germination

	Month
Weeds:	Aug.	Sept.	Oct.	Nov.	Dec.	Jan.
Barnyardgrass	24	24	48	72	96	NG
Canarygrass	NG	168	96	96	96	NG
Lambsquarters	72	96	96	72	168	NG
Silverleaf Nightshade	96	96	72	96	NG	NG
Pigweed	48	72	48	72	96	NG
Purslane	24	24	24	48	96	168
Shepardspurse	NG	NG	168	96	168	NG

NG = No germination

To contact Barry Tickes go to: btickes@ag.arizona.edu.

For questions or comments on any of the topics please contact Marco Pena at the Yuma Agricultural Center.
College of Agriculture, The University of Arizona, Tucson, AZ.