The lima bean (Phaseolus lunatus) is a warm-season annual plant belonging to the legume family, Fabaceae. Native to Central and South America, it is cultivated globally for its edible seeds. The life cycle is a progression through distinct biological stages, transforming the dormant seed into a mature, seed-producing organism. This progression involves the plant transitioning from relying on stored food to generating its own energy and reproducing itself.
From Seed to Seedling: Germination
Germination begins when the dormant seed absorbs water, causing it to swell and break the protective seed coat. Successful germination requires warm soil, ideally at least 65°F. Within 7 to 18 days, the radicle (embryonic root) emerges first to anchor the plant and absorb water.
Next, the hypocotyl (embryonic stem) elongates, forming a hook that pulls the two thick cotyledons above the soil surface. This is known as epigeal germination. The cotyledons function as the initial food source, providing the energy required for the seedling to establish itself before it can begin photosynthesis.
Developing the Plant: The Vegetative Stage
Once the cotyledons are fully exposed, the seedling enters the vegetative stage, concentrating on structural growth. The first pair of true leaves are simple, single leaflets, followed quickly by compound leaves with three leaflets, known as trifoliolates. These leaves initiate photosynthesis to create sugars necessary for rapid biomass accumulation.
During this period, the root system expands significantly, establishing a network to draw up water and nutrients. Lima beans are categorized into bush varieties (determinate and compact) and pole varieties (indeterminate and vining). This stage maximizes leaf surface area and builds a sturdy structure to support reproductive efforts.
Reproduction: Flowering and Pod Set
The shift to reproductive growth is triggered once the plant has accumulated enough energy and reached maturity. Small clusters of off-white or yellowish-green flowers form on short stalks called racemes. The specialized lima bean flower contains both male and female structures and is largely self-pollinating, often transferring pollen before the flower fully opens.
Successful fertilization causes the ovary to swell, developing into the young pod. High temperatures, particularly above 90°F, can negatively impact this process, causing flowers to drop off before they can set fruit. Conversely, high humidity can promote better pollen germination, leading to a higher rate of pod set.
Final Stage: Seed Maturity and Harvest
As the plant matures, the newly formed pods rapidly expand as the seeds fill out. This marks the final stage, where the plant’s focus shifts entirely to seed development. For fresh consumption, such as baby lima beans, the pods are harvested when they are plump, firm, and still bright green, before the seeds fully harden.
For dry storage, the entire pod remains on the vine until it completely dries out and turns yellow or brown. The pod becomes brittle, and the hard seeds within have lost most of their moisture content. The fully matured, dry seed contains the embryo and stored food, completing the life cycle and readying itself to begin the process again in the next growing season.