It’s our human activities that have created weed problems since no plant is a “weed” in nature. Weeds compete with our crops and so have become an enemy to farmers. And as farmers have piled on the herbicides to address the problem, they have complicated things, damaging the soils and the crops they were trying to protect. Meanwhile, overuse has created herbicide-resistant weeds.
Both humans and nature are involved in plant breeding programs. The main difference between the two programs is that man breeds plants for yield, while nature breeds plants for survival. Nature is persistent, and weeds are naturally strong competitors. Even though we try to manipulate the process, certain weeds prevail and thrive.
Weeds tend to share some common attributes that contribute to their bad name. Here are just a few of the characteristics that make a weed a weed:
- Seed production – sometimes tens of thousands of seeds per plant.
- Survival – survive for a very long time in the soil, going dormant but then sprouting just as soon as conditions are right.
- Quick establishment – they seem to crop up in the blink of the eye.
- Spread easily – ability to reproduce vegetatively without seeds.
- Tough soldiers – grow in inhospitable locales where more desirable plants typically wouldn’t survive.
Many of our weed problems are created when the mineral relationships in our soils are out of whack. Magnesium, for instance, causes soil particles to stick together. Tight soils tend to promote grasses, as grasses are nature’s way to try to loosen the soil and promote the movement of oxygen and water. While a balance of magnesium is important, as magnesium helps to accelerate photosynthesis, excess magnesium can promote the growth of grasses.
On the plus side, we’ve learned that the appearance of various weeds are indicators of mineral deficiencies or excesses in our soils, and this knowledge can be used as a diagnostic tool to address soil problems. For example, excessive applications of potash can produce a deficiency in calcium, promoting an explosion of dandelions. Broadleaf weeds like a soil environment in which available potassium exceeds available phosphate in a ratio of 1 to 8. As phosphate becomes more available, broadleaf leave weeds are reduced. Bindweed, as another example, can be an indicator of deficiencies in calcium and phosphorus and excesses in potassium and magnesium. Improving the soil balance can reduce the amount of bindweed.
The bottom line is that healthy soils will support fewer weeds. As we improve the microbiology in the soil, the mineralization of elements improves and, overall, there tends to be less weed pressure. Weed control begins in the soil. So does insect and disease control, but that’s another newsletter or two.