There are no simple answers for how long weed seeds can live in the soil. Seed longevity is way to measure viability or ability to germinate. It measures the length of time a seed can persist in the soil and still germinate.  Commonly, seed longevity is a measure of loss through microbial decay and physiological death.  An “average” weed seed in agricultural systems with chisel plowing, disking, and harrowing probably remains viable for 1 to 5 years depending on species and dormancy.  Some weed seed (i.e. common lambsquarters) under ideal conditions remain viable for 1,000 years.

 An understanding of weed seed longevity requires considering soil seedbank dynamics.  Dr. Karen Renner at Michigan State University has an Extension publication [“Weed Seedbank Dynamics” (Bulletin E-2717)] (http://web2.msue.msu.edu/bulletins/Bulletin/PDF/E2717.pdf) that provides an excellent overview of the fate of weed seed in the soil.  Weed seed in the soil seldom survive to physiological death. Also physiological death of dormant seed takes longer than physiological death of nondormant seed. Most weed seed (80 to 90%) are lost through predation either on the mother plant or before being incorporated into the soil seedbank. Once in the soil, seed predation is minor and most seeds are lost through failed germination. Other seed losses occur through decay, physical damage, erosion and water runoff, germination and emergence, and physiological death (Figure 1).

      Eaten by                         Loss in erosion &                   Germination

Figure 1. The fate of weed seed once it reaches the soil seedbank.

            Not all seed for an individual weed species lose their viability, or ability to germinate (suffer physiological death), at the same time.  Generally the loss of viability in weed seed follows an exponential curve (see example at: http://oak.cats.ohiou.edu/~piccard/radnotes/figs/expondecay.gif). Within a population of seed, most seed lose viability in the first few years after burial with a few seed losing viability over many years after burial. Thus, finding a viable seed is partly dependent on the number of seeds for any particular species in the soil.

Weed species, seed dormancy, burial depth, environment, soil type, and crop production practices all influence weed seed longevity. Deeply buried (>3 inches) weed seed generally become dormant. Some weed species also produce dormant seed.  Dormant seed, especially due to hard seed, seed coats impervious to water (i.e. velvetleaf or many legumes), will persist longer than nondormant seed. Seed without dormancy, such as crop or some grass seed, generally persist for a single or few years. Seed buried deep in the soil will persist longer than shallowly buried seed or seed on the soil surface (Table 1). 

There are two studies of seed longevity in temperate climates that illustrate depth of soil burial (Table 1) and soil type (Table 2) effects on weed seed longevity. In the first study, Dr. Lewis of the Wales Plant Breeding Station buried seed in plastic mesh packets at different soil depths in ceramic containers for up to 20 years. He removed the seed packets from the soil and attempted to germinate seeds in a greenhouse. Few grasses survived 4 years (timothy was a notable exception) and only timothy seed buried at 5 inches still germinated after 20 years. Low percentages (~1%) of legumes (clovers and alfalfa) germinated throughout the study. Common lambsquarters, creeping buttercup, and curly dock all had seeds surviving for 20 years.  In another study curly dock seed was viable after 80 years. These species all have hard seed.

            In the second study, Dr. Burnside and colleagues, placed seed in plastic capsules with the ends covered with a plastic screen. The capsules were buried in fields at Lincoln and Mitchell  (eastern and western), Nebraska. Approximately yearly, they germinated seeds in a growth chamber. More weed seeds survived for five years at the drier western Nebraska site. Common lambsquarters, hairy nightshade (a relative of eastern black nightshade), jimsonweed, and velvetleaf survived 17 years at least one location. Common mullein, a biennial, seed survived for 17 years.  In another study, common mullein seed was viable after 100 years.
Table 1. Seed germination after storage 5 and 10 inches in untilled soil in Great Britain.

                                                               Years of seed burial                   

                                    1                                 4                                  20   

                                                          Soil Depth (inches)                            

Weed species      5          10                    5          10                    5          10

                         ---------------------------- % germination ---------------------------

Blackgrass            31        28                   22        10                    0          0

Soft brome            3          11                   0          0                      0          0

Red fescue           17        14                    0          0                      0          0

Perennial ryegrass 23       30                    4          1                      0          0

Crabgrass             22        50                   1          2                      0          0

Timothy                 86        87                   72        51                    1          0

Tall fescue            18        21                    0          0                      0          0

Italian ryegrass     29        70                    3          1                      0          0

Wild oat                19        12                    3          1                      0          0

White clover          23        6                      7          6                      1          1

Red clover             24       23                    14         7                      1          1

Alsike clover           5          3                     3          4                      3          1

Alfalfa                    0          1                     0          1                      1          1

Lambsquarters       88        87                    35        81                   32        22

White campion       25        27                    52        17                    1          1

Scentless mayweed 87        82                   47        11                    0          0

Narrowleaf plantain  96        94                   72        21                    0          0

Ladysthumb            53        20                   18        18                    1          2

Creeping buttercup  1*         2*                   52        53                   51        55

Curly dock             49        34                    15        49                   30        26

*Most seed are dormant

Modified from Tables 1, 2, and 3 in Lewis, J. 1973. Longevity of crop and weed seeds: Survival after 20 years in soil. Weed Research 13:179-191.

Table 2. Seed germination of 41 weed species during burial 8 inches deep in untilled soil in Lincoln and Mitchell, NE.

                        Sharpsburg silty clay loam       Very fine sandy loam

                             at Lincoln                                   at Michell   

                         Years of seed burial                 Years of seed burial

Weed Species       1          5          17                    1          5          17

Annual grass      ------------------------ % Germination----------------------

Barnyardgrass       4          35        1                      3          31        0

Bristly Foxtail         79        44        13                     73        22        0

Cheat                   16        14        0                       35        26        13

Downy brome        2          2          --                      1          0         --

Green foxtail          73        34        5                      51        26        0

Japanese brome    5          0          --                     10        0          0

Jointed goatgrass  54        1          0                      72         2          0

Large crabgrass    48        9          0                      79        12         0

Longspine sandbur 16       4          0                      12        13         1

Shattercane           43        0          1                      37        3          0

Yellow foxtail          73        13        0                      79        9          0

Buffalobur               3        1          0                      2          3          2 

Common cocklebur 60        4         0                      60        33        1

Lambsquarters        53      17        28                     49        31        7

Common Sunflower   1      15         3                      1          6          0

Field pennycress    72       43        2                      61        14        8

Hairy nightshade     90        8        4                      94        70        65

Ivyleaf morningglory  4       11        7                      5          9          3

Jimsonweed           81        0          0                    93        89        90

Kochia                   0          0          1                      8          1         0

Pennsylvania

 smartweed            3          30        7                      20        7          0

Puncturevine         42         3          0                      43        15        2

Redroot pigweed    73        1          0                      69        37        1

Russian thistle        0          0          0                      0          0          0

Tall waterhemp      38        10        3                       42        23        1

Velvetleaf              32        40        25                     35        50        35

Biennial broadleaf                                                                     

Common mullein     91        73        72                    95        88        95

Musk thistle            6          33        --                     39        38        --

Scotch thistle         68         45        --                     65        51        --

Tall thistle               7          33        --                     28        19        --

Perennial broadleaf

Canada thistle       47        35        9                      35        29        7

Common milkweed 36        28        0                     31        5          0

Curly dock            83        89        77                    92        74        61

Dandelion             3          5          0                     12        1          0

Flodman thistle      0          27        1                      3          11        2

Hemp dogbane      22        0          0                     52        0          0

Hoary cress          41        3          0                      37        13        0

Horsenettle           12        2          1                      12        7          5

Leadplant              2         0          0                      3          0          --

Swamp smartweed 3         20        14                    7          7          0

Woollyleaf bursage 6        4          1                      15        8          0 

Blank cells means data is missing

Modified from Tables 4 and 5 from Burnside, O.C., R. G. Wilson, S. Weisberg, and K. G. Hubbard. 1996. Seed longevity of 41 weed species buried 17 years in eastern and western Nebraska. Weed Sci. 44:74-86.

Implications for management

            The longevity of weed seed has implications for management.  The first step in managing seed longevity is to prevent weed seed production and input into the soil seedbank.  The less seed input, the fewer long-lived seeds in a field’s seedbank. Tillage, competitive crops, cover crops, flaming, hand-weeding, and mowing that reduce weed populations and prevent seed production will reduce the input of long-lived seed into the seedbank. If it is impossible to manage all weeds in a field, concentrate your efforts on broadleaf weed species that produce long-lived seed such as common lambsquarters, jimsonweed, and velvetleaf.

Many biennials, such as common mullein and Scotch thistle, have extremely long-lived seed.  Tillage is effective in preventing seed production of biennials. Generally, seed longevity is not the biggest problem with perennial weeds. Managing vegetative reproduction and spread along with seed production are keys to controlling perennial weeds.  Curly dock and creeping buttercup, perennial weeds with the greatest seed longevity, are normally not problems in agricultural fields.

Another step in reducing seed longevity is preventing seed dormancy. Avoid deep burial of seed that can cause enforced seed dormancy.  Use shallow tillage that decreases seed persistence in the soil because it increases seed germination. Shallow tillage exposes weed seed to light and soil aeration. Movement of seed closer to soil surface can also cause seed coat abrasion and loss of inhibitors. The emerging weed seedlings after shallow tillage can be killed using stale seedbed treatments, further reducing the seedbank.