Here's a great garden tip:
If you plant rye (as a mulch) between the garden rows and keep it mowed, the allelochemicals that leach from rye residue prevent weed germination but do not harm transplanted tomatoes, broccoli, or many other vegetables.
Allelopathy refers to a plant’s ability to chemically inhibit the growth of other plants. A good example is the black walnut which prohibits many things from growing under or around it.
Rye is one of the most useful allelopathic cover crops because it is winter-hardy and can be grown almost anywhere. Rye residue contains generous amounts of allelopathic chemicals.
When left undisturbed on the soil surface, these chemicals leach out and prevent germination of small-seeded weeds. Weed suppression is effective for about 30 to 60 days. But if the rye is tilled into the soil, the effect is lost.