I was just wondering, for fast results in plants, which would you prefer: applying worm castings on the top soil or using worm casting tea, and why?
If you're talking about leachate (worm castings steeped in water), some gardeners say that this tea will have approximately the same benefit to plant growth as the pure composted worm castings themselves.
But studies have shown that, in the long run, using the castings directly in the soil will produce better plant growth, often far better, than does leachate obtained by steeping the castings in water. Some of those studies were carried out by Ohio State University, Mississippi State University, Colorado State University, Cornell and others. (citation needed)
But if your main objective is speed of results, then the teas solution will find their way into the plant’s system more quickly than waiting for the dried casting to be "watered in" over time. Castings tea can also be used as a foliar spray/wash for even faster results.
But "tea" production methods vary — so consider, if your tea is "aerobically brewed", you're also increasing the diversity of beneficial microbes and adding to the soil the environment needed to keep the beneficial organisms alive and multiplying in your soil; more so than can be typically obtained from the castings themselves.
The best solution to this argument is to do both — to receive the full benefits of worm casting, apply it directly to the soil as both as an admendment and an occasional top dressing around the base of the plants. Then give them a good drink of tea however often as you see fit — weekly would be ideal, depending on your supply — neither the tea nor the castings will burn your plants.