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Seeds of the two grass species were shorter lived than those of velvetleaf or waterhemp. At the end of the third year (1997) no grass seeds were recovered. Somewhat surprising is that waterhemp seed was more persistent than velvetleaf in this study. Velvetleaf has long been used as the example of a weed with long-lived seeds. In the fourth year of the study four times more waterhemp seedlings than velvetleaf emerged and four times more waterhemp seed than velvetleaf seed (240 vs 60) remained in the seed bank.

Methods: Seeds of velvetleaf, waterhemp, woolly cupgrass and giant foxtail were harvested from mature plants during the 1994 growing season. The seeds were cleaned and counted and then buried in the upper two inches of soil on October 21, 1994. Two thousand seeds were buried within a 3 sq ft frame to allow recovery during the course of the experiment. Weed emergence was determined by counting seedlings weekly during the growing season. Emerged seedlings were pulled by hand after counting. In the fall of each year one quarter of the soil within a frame was excavated and the remaining seeds were extracted and counted. Corn or soybeans were planted between the frames during the course of the experiment to simulate agronomic conditions.

So what does this mean as far as managing weeds in Iowa. First, consider how the methods used in this experiment might influence the results. The seeds were buried in the upper two inches of soil, the zone most favorable for germination. Most long term studies investigating the persistence of seeds have buried the seeds at greater depths than used here in order to minimize germination. If the seeds were buried deeper one might expect less emergence and greater persistence since the seeds would be at a soil depth with less biological activity. If the seeds had been placed on the soil surface it is likely that there would be more predation, less emergence and shorter persistence.

Figure 1. Fate of seeds during the four years following burial in the upper two inches of soil. Two thousand seeds of each species were buried in the fall of 1994. The area in white represents the number of intact seeds present in the fall of each year, green represents the total number of seeds that produced seedlings during the four years, and the blue represents the total number of seeds lost. Buhler and Hartzler, 1999, USDA/ARS and ISU, Ames, IA.

The results indicate that the seed bank of giant foxtail and woolly cupgrass should be able to be depleted much quicker than that of the two broadleaves. Maintaining a high level of weed control for two years should greatly diminish populations of these weeds in future years and simplify weed management. Unfortunately, a single plant escaping control can produce more seed than was introduced to the soil in these experiments, thus the seed bank can be rapidly replenished any time weed control practices fail to provide complete control. Finally, over 50% of velvetleaf and waterhemp seed was lost in the first two years following burial. However, significant numbers of seed of these species remained four years after burial. This will make populations of these two species more stable over time than those of woolly cupgrass and giant foxtail.

For all species except woolly cupgrass the majority of seeds were unaccounted for (the blue portion of the graph) in this experiment. Determining the fate of the ‘lost’ seeds is a difficult task. A seed basically is a storage organ of high energy compounds, thus they are a favorite food source of insects and other organisms. In natural settings more than 50% of seeds are consumed by animals. The importance of seed predation in agricultural fields is poorly understood, but recent studies have shown that predation can be a significant source of seed loss. Another important mechanism of seed loss likely is fatal germination. This occurs when a seed initiates germination but the seedling is killed before it becomes established. Fatal germination probably is more important with small-seeded weeds such as waterhemp and lambsquarters than with large-seeded weeds, but is poorly understood. A better understanding of the factors that influence seed losses might allow these processes to be manipulated in order to increase seed losses.

Results: The emergence patterns of the four species were described in an earlier article (see emergence patterns). The fate of the seeds (emergence, loss or survival in soil) during the first four years after burial is shown in Figure 1. In the first year following burial waterhemp had the lowest emergence (5%) whereas greatest emergence was seen with woolly cupgrass (40%). Total emergence over the four years ranged from 300 seedlings (15% of seed) for waterhemp to 1020 seedlings (51%) for woolly cupgrass. More than three times as many seedlings emerged in the first year than in subsequent years for velvetleaf, woolly cupgrass and giant foxtail, whereas 140 waterhemp seedlings emerged in 1996 compared to only 100 in 1995.

You will want to provide the proper amount of light and water to your plants, of course. A drip irrigation system can cut your water bills while improving the health of your plants. Kits are available that give you everything you need to get started. If you prefer, you can start from scratch and obtain separate components to put them all together.

Loam is ideal for containers as well as for outdoor growing. Unfortunately, it is usually the most expensive soil to buy. But if you are interested in growing the best plants possible, it can pay big dividends in the long run.
You can also build up your own loam soil by adding organic matter to it. If you have a compost bin, you can use the compost to improve your soil. This will be a time-consuming and ongoing process but with grit and persistence will pay off in the long run.

Just like humans, plants need the right nutrients. The most important ones for your cannabis plants are nitrogen (N), potassium (K) and phosphate (P). These make up the ratios you will typically see on fertilizer labels.

The optimal ratio for loam is 20% clay, 40% silt and 40% sand. Most folks think a pH of 6.0 is best for cannabis, with a range of 5.8 to 6.3 being acceptable. With a pH close to neutral, loam is typically in that zone or close to it.

Loam for Growing Marijuana & Other Crops

In addition, you do not necessarily have to provide costly soil for your plants outside. But for the best results, you want good marijuana soil that will help your plants grow healthy and happy. DripWorks is here to offer you a few simple tips for finding and creating the best soil for growing marijuana outdoors.

Of these types, loam is by far the best soil mix for growing marijuana plants and many other types of crops. Loam is a mixture of clay, sand, and silt, bringing forth the best qualities of these disparate types of soil while minimizing their worst attributes.

Silt soils have lots of minerals and retain moisture well. Like clay, however, this type of soil can become compacted and hard in certain conditions. It can also form a crust, making it difficult for moisture and nutrients to reach plants’ roots.

Soil Types

Four basic soil types exist: sand, clay, silt, and loam. Each has its pros and cons for gardening.

Test kits are available to measure your soil’s acidity, or you can take a sample to your friendly local extension agent. If your dirt does not have the proper acidity, soil amendments are available to lower or raise the pH level in your soil. Your local nursery, garden store or extension agent can make some suggestions.