2. They exclude light and heat from cultivated plants, and thus interfere with their growth.
3. They take up mineral and other matters from the soil, and hold them during the growing season, thus depriving crops of their use.
It is not necessary to argue the injury done by weeds. Every farmer is well convinced that they should be destroyed, and the best means of accomplishing this are of the greatest importance.
How may we protect ourselves against their increase?
Why is it especially important for this purpose to maintain the balance of the soil?
In the first place, we should protect ourselves against their increase. This may be done:—
By decomposing all manures in compost, whereby the seeds contained will be killed by the heat of fermentation; or, if one bushel of salt be mixed through each cord of compost (as before recommended), it will kill seeds as well as grubs,—
By hoeing, or, otherwise, destroying growing weeds before they mature their seeds, and
By keeping the soil in the best chemical condition.
This last point is one of much importance. It is well known that soils deficient in potash, will naturally produce one kind of plants, while soils deficient in phosphoric acid will produce plants of another species, etc. Many soils produce certain weeds which would not grow on them if they were made chemically perfect, as indicated by analysis. It is also believed that those weeds, which naturally grow on the most fertile soils, are the ones most easily destroyed. There are exceptions (of which the Thistle is one), but this is given as a general rule.