According to garden experts, you don't have to compost to improve soil quality.

By incorporating these plants into your garden you can significantly improve soil quality, leading to overall healthier plant growth in that soil.
Legumes (e.g., clover, alfalfa, peas, beans)
Benefit: Legumes have a symbiotic relationship with nitrogen-fixing bacteria in their root nodules. This process converts atmospheric nitrogen into forms usable by plants, enriching the soil with nitrogen.
Cover Crops (e.g., rye, oats, barley, buckwheat):
Benefit: Cover crops protect the soil from erosion, add organic matter, and improve soil structure. They also suppress weeds and can help break pest cycles.
Deep-rooted Plants (e.g., radishes, turnips, marigolds, comfrey):
Benefit: Deep-rooted plants break up compacted soil layers and enhance soil aeration and drainage. They also bring up nutrients from deeper layers, making them available to other plants.
Grasses (e.g., alfalfa, ryegrass, fescue, bluegrass):
Benefit: Grasses have extensive root systems that stabilize the soil, reduce erosion, and increase organic matter. They also enhance soil structure and promote beneficial microbial activity.
Dynamic Accumulators (e.g., comfrey, yarrow, dandelion):
Benefit: These plants accumulate high levels of certain nutrients in their tissues. When they die and decompose, they release these nutrients back into the soil, enriching it.
Green Manure Crops (e.g., hairy vetch, crimson clover, mustard):
Benefit: Green manures are grown specifically to be incorporated into the soil. They add organic matter and nutrients, improve soil structure, and enhance microbial activity.
Bioaccumulators (e.g., sunflowers, mustard):
Benefit: These plants can extract and concentrate heavy metals and other contaminants from the soil, helping to clean up polluted soils.
And also:
Milk Thistle - potassium-rich with strong deep roots that help break up soil and bring iron closer to the surface.
Lupine - this plant's roots benefit the soil by fixing nitrogen (and they're beautiful, easy to grow, and the deer don't like them).