QUESTION: Can I plant seeds directly in compost?
ANSWER: Planting directly into compost is not a good idea. Compost is an excellent soil amendment. It improves the nutrient content of soil, yet some of the nutrients which it contains are only good in small amounts, as larger amounts can lead to ammonia toxicity and too much salt. Compost is also surprisingly low in certain essential nutrients and minerals that plants need. For this reason, growing plants in straight compost can lead to weak or even dead plants due to nutrient deficiencies.
When mixed with topsoil, compost is excellent in terms of handling water and moisture levels. Adding compost to topsoil improves the drainage of the topsoil but also increases its ability to retain water. When used by itself, however, compost drains quickly and is quick to dry out.
Because compost is lighter than most soils, it is not able to provide the stability necessary for strong root systems. Compost also compacts over time, which can be especially bad for containers whose contents seem to shrink over time. Though it may be tempting, planting in pure compost is a bad idea.