A lima bean starts as a dry seed and ends, usually within a single warm season, as a plant loaded with pods of beans that fill and then dry. In between come sprouting, a leafy vine or bush, and flowers. The plant is surprisingly delicate at two moments, its first contact with water and its flowering, and weather at those points does more to decide the harvest than almost anything else. Along the way it also does things few gardeners notice, from making its own fertilizer with root bacteria to calling in insect bodyguards when pests attack.
Planting and Sprouting Why Warm Soil Matters
Before anything visible happens, a planted lima seed swells as it pulls in water from the soil. That first drink is the riskiest moment in the plant’s life. Lima seeds can be injured if they take up that water at temperatures below about 25°C (77°F).1PubMed Central. Imbibition Period as the Critical Temperature Sensitive Stage in Germination of Lima Bean Seeds Soaking in water at 5–15°C (41–59°F) during the first stages clearly damages the seed’s growing tip and the whole seed.2PubMed Central. Imbibition Temperature Sensitivity of Lima Bean Seeds Controlled by Initial Seed Moisture Once a seed has taken up water in warm conditions, a later cold spell doesn’t cause the same injury.3PubMed Central. Imbibition Period as the Critical Temperature Sensitive Stage in Germination of Lima Bean Seeds What matters most is how warm the soil is on planting day and the day or so after.
In the garden, chilling injury looks like seeds that rot or stay swollen and never break the surface. Some seedlings do emerge, but stunted or with damaged growing tips. A soil thermometer pushed in at planting depth removes the guesswork.
Seed moisture changes how sensitive the seed is. Seeds that first take up moisture slowly from damp air, reaching about 20% water, escape this chilling injury.4PubMed Central. Imbibition Temperature Sensitivity of Lima Bean Seeds Controlled by Initial Seed Moisture Those pre-moistened seeds also grow better even in warm conditions and leak less of their contents into the water.5PubMed Central. Imbibition Temperature Sensitivity of Lima Bean Seeds Controlled by Initial Seed Moisture Wait until the soil is reliably warm, roughly two weeks after the last frost, before sowing, and avoid soaking very dry seed in cold tap water before planting.
A cold snap after planting is less worrying than cold at planting. If the seed has already swelled in warm soil, a cool night may slow growth but won’t cause the same soaking injury, so there’s no need to replant after every chilly evening.
Lima beans sprout by pushing their two fat seed halves up out of the soil.6Crop Science. Dry Matter Contribution by Cotyledons of Lima Beans and Other Epigeal Legumes Once in the light, those seed halves turn green and help feed the seedling alongside the first true leaves.7Crop Science. Dry Matter Contribution by Cotyledons of Lima Beans and Other Epigeal Legumes The hooked stem that hauls them up is fragile and easily snapped. A crusted soil surface can trap it, so keep the surface loose. Planting about an inch deep lets the seed halves reach light.
The Leafy Growth Stage and the Bacteria in the Roots
Lima bean roots host bacteria that live in small swellings called root nodules and turn nitrogen from the air into a form the plant can use.8PubMed. Bradyrhizobium paxllaeri sp. nov. and Bradyrhizobium icense sp. nov., nitrogen-fixing rhizobial symbionts of Lima bean (Phaseolus lunatus L.) in Peru These bacteria belong to a group found with limas in their native range, including species first described from Peruvian lima beans.9PubMed. Bradyrhizobium paxllaeri sp. nov. and Bradyrhizobium icense sp. nov., nitrogen-fixing rhizobial symbionts of Lima bean (Phaseolus lunatus L.) in Peru The amount of nitrogen they supply can be modest, around 9–10 kg per hectare in one field setting, and varies by variety.10Agricultural Sciences. Nodulation and Fixed Atmospheric Nitrogen of Some Local Lima Bean (Phaseolus lunatus L.) Cultivars Grown in a Coastal Savannah Environment Limas still benefit from good soil but usually need little nitrogen fertilizer.
You can check your plant’s nodules by gently digging up one plant mid-season and rinsing the roots. Healthy, working nodules are pink or red inside when cut. White or green nodules, or none at all, suggest the bacteria are missing. Where beans haven’t grown before, a bean inoculant sold at garden centers can be added at planting.
Too much nitrogen backfires. Heavy nitrogen fertilizer pushes lush leaves over flowers, and plants fed lots of nitrogen form fewer nodules. Compost is usually enough.
Light decides whether root partners help or hurt. In full sun, plants with both nodule bacteria and helpful root fungi grew about 43% more top growth than plants without them.11PubMed Central. Friend or Foe—Light Availability Determines the Relationship between Mycorrhizal Fungi, Rhizobia and Lima Bean (Phaseolus lunatus L.) In shade, the same partners cut top growth by about 47%.12PubMed Central. Friend or Foe—Light Availability Determines the Relationship between Mycorrhizal Fungi, Rhizobia and Lima Bean (Phaseolus lunatus L.) The partners cost the plant energy it can only repay with plenty of light, so give limas a full-sun spot. Cutting the plants at soil level and leaving the roots in place returns more of the leftover nitrogen to the bed than pulling them out.
Flowering and Pollination
Day length can control flowering. In a test of 27 lima lines from many regions, 16 flowered regardless of day length.13Journal of the American Society for Horticultural Science. Genetic Variation for Flowering Response to Photoperiod in Phaseolus lunatus L. But 8 reacted sharply to day length, and some limas flower only when days get short.14Journal of the American Society for Horticultural Science. Genetic Variation for Flowering Response to Photoperiod in Phaseolus lunatus L.15HortScience. Inheritance of Growth Habit and Qualitative Flowering Response in Lima Beans (Phaseolus lunatus L.) The genes for short-day flowering are linked to those for growth habit, bush versus climbing vine.16HortScience. Inheritance of Growth Habit and Qualitative Flowering Response in Lima Beans (Phaseolus lunatus L.) So a variety from the tropics may grow huge vines all summer and flower only in autumn in a northern garden. Choose varieties sold for your region.
That growth habit is the difference between determinate (bush) and indeterminate (pole) types. Bush types stop growing at a set size and flower in a concentrated burst, so they usually give an earlier harvest. Pole types keep climbing and flowering over a long season, and they need a trellis 6 feet or more tall.
A big, leafy vine with no flowers by late summer may not be sick, but a day-length-sensitive variety waiting for shorter days. Frost can arrive before it sets pods. There’s little you can do to speed up flowering, so the main fix is next year’s choice of variety.
Lima flowers mostly fertilize themselves, but in one study about 38% of seeds came from cross-pollination.17Genetic Resources and Crop Evolution. Estimation of natural outcrossing rate and genetic diversity in Lima bean (Phaseolus lunatus L. var. lunatus) from Brazil using SSR markers: implications for conservation and breeding Bees visiting the flowers therefore matter more than many gardeners assume. Saving seed from two varieties grown side by side can give mixed offspring, so separate any varieties you plan to save seed from. Basil and other flowering herbs nearby can draw pollinators, and it’s best to avoid insecticide sprays while plants are in bloom.
Why Hot Weather Leaves Pods Empty
Heat-related yield loss in lima beans comes mainly from damaged pollen that fails to survive or be released.18Crop Science. Multiple physiological mechanisms involved in reproduction could be targeted for breeding heat tolerance in lima bean In heat-sensitive plants at 35°C (95°F), pod numbers held up but beans per pod, bean weight and total yield fell.19HortScience. A SURVEY OF HEAT TOLERANCE IN LIMA BEAN (PHASEOLUS LUNATUS) A plant that looks fine and covered in pods can still give a poor harvest. Some varieties put their energy into seeds efficiently and still yield well in heat.20Bragantia. Assessment of lima bean genotypes for high-temperature cultivation based on physiological and agronomic traits Pollen damage often isn’t obvious on the plant; the shortfall may show up only when you shell a few pods and find fewer or smaller beans.
What you see can hint at the cause. Flowers dropping during a heat wave suggest heat, as do flat pods with few beans after hot spells, though drought and other stresses can look similar. Chewed or spotted pods point to pests or disease instead.
You can dodge heat with timing and variety. Plant so flowering falls before or after the hottest weeks, and choose varieties described as heat tolerant in hot regions. Mulch and steady watering keep roots cooler. Flowering often resumes and sets pods once nights cool.
How the Plant Defends Itself
Lima beans make compounds that release cyanide when tissue is chewed.21PubMed Central. Biosynthesis of cyanogenic glucosides in Phaseolus lunatus and the evolution of oxime‐based defenses These compounds protect leaves from plant-eating insects.22PubMed. Role of cyanogenic glycosides in the seeds of wild lima bean, Phaseolus lunatus: defense, plant nutrition or both? Levels rise soon after sprouting, so young seedlings are well guarded.23PubMed. Role of cyanogenic glycosides in the seeds of wild lima bean, Phaseolus lunatus: defense, plant nutrition or both?
When pests attack, lima leaves give off scents that make nearby leaves, even on neighboring plants, produce more nectar from small glands outside the flowers.24PubMed Central. Within-plant signaling by volatiles leads to induction and priming of an indirect plant defense in nature That nectar attracts and feeds predatory insects and mites that eat the pests.25PubMed Central. Within-plant signaling by volatiles leads to induction and priming of an indirect plant defense in nature26PubMed. Induced production of extrafloral nectar in intact lima bean plants in response to volatiles from spider mite-infested conspecific plants as a possible indirect defense against spider mites Plants given these scents or the nectar grew more leaves and flowers and suffered less damage.27PubMed Central. The Defensive Role of Volatile Emission and Extrafloral Nectar Secretion for Lima Bean in Nature Leaving predatory insects alone, and planting dill nearby to attract more, works with the plant’s own defense.
Aphids can trouble limas in hot weather. Nasturtiums can lure them away from the beans, and avoiding broad insecticides keeps the helpful predators alive.
Lima beans are highly susceptible to downy mildew, which causes white fuzzy growth on pods, mainly in cool, wet, humid weather.28PubMed Central. RNA-Seq reveals infection-related global gene changes in Phytophthora phaseoli, the causal agent of lima bean downy mildew Resistant varieties and fungicides don’t always control it.29PubMed Central. RNA-Seq reveals infection-related global gene changes in Phytophthora phaseoli, the causal agent of lima bean downy mildew Resistance to some strains depends on single genes, so a resistant variety may protect against some strains but not others.30HortScience. Inheritance of Resistance in Lima Bean to Phytophthora phaseoli, the Causal Agent of Downy Mildew of Lima Bean Space plants for airflow, water at the base in the morning, and pull and bin infected pods rather than composting them. Rotate beds away from where limas grew last year.
Pod Filling and When to Harvest
Developing lima seeds first go through a ripening stage when they gain stored food faster than water, until they are about 60% water.31American Journal of Botany. CELL FINE STRUCTURE OF DEVELOPING LIMA BEAN SEEDS RELATED TO SEED DESICCATION Then, in the maturation stage, they lose water without adding more food.32American Journal of Botany. CELL FINE STRUCTURE OF DEVELOPING LIMA BEAN SEEDS RELATED TO SEED DESICCATION Fresh green limas are picked near the end of filling, and dry beans are picked after drying.
For fresh beans, look for pods that are plump, firm and bright green with beans bulging inside. The beans should be full-sized but still green. Yellowing pods mean the beans are getting starchy. Picking often keeps pole types producing.
Squeeze a pod gently and feel for rounded, plump beans rather than flat ones. Open one pod as a test before picking the whole plant, since pods on the same plant ripen at different times.
That uneven ripening is why one plant gives several pickings, and you may need to pass over it more than once. Pole types flower over a long season, so they offer green beans and drying pods side by side. Bush types ripen over a shorter window, so you can plan one or two larger pickings.
For dry beans, leave pods until they are brown, papery and rattle. Pick before wet weather to avoid mold. Finish drying shelled beans indoors until they shatter rather than dent when bitten.
Cooking Lima Beans Safely
The same defense compounds stay in the beans, so lima beans should not be eaten raw. Cooking destroys the enzymes that release cyanide.33OSU Extension Service. Is there cyanide in lima beans? Boiling for more than 30 minutes in plenty of water removes about 80% of the cyanide.34OSU Extension Service. Is there cyanide in lima beans? Soaking 24–48 hours, draining, then boiling briefly in fresh water also works.35OSU Extension Service. Is there cyanide in lima beans? Steaming removes less than boiling.36OSU Extension Service. Is there cyanide in lima beans? Boil and discard the cooking water.
Reusing the water in soup or sauce would put the dissolved compounds back on the plate. Cooking with the lid off, in a large pot, helps volatile cyanide escape rather than linger.
Varieties sold in shops are bred low in these compounds. Some colored or wild-type limas carry more, so saved seed from unusual varieties deserves the longer boil.
Storing Dried Beans So They Still Cook Soft
Hot, humid storage consistently produces hard-to-cook beans, ones that stay hard however long they cook.37Journal of Food Processing and Preservation. A REVIEW OF TEXTURAL DEFECTS IN COOKED RECONSTITUTED LEGUMES? THE INFLUENCE OF STORAGE AND PROCESSING In damp warmth, chemical changes lock the bean’s cell walls so they don’t soften.38Journal of Food Biochemistry. A REVIEW OF TEXTURAL DEFECTS IN COOKED RECONSTITUTED LEGUMES ?THE INFLUENCE OF STRUCTURE AND COMPOSITION Beans stored at 29°C and 65% humidity needed much longer cooking, while those kept cool or dry stayed easy to cook.39Journal of Food Science. Changes of Selected Physical and Chemical Components in the Development of the Hard‐to‐Cook Bean Defect Store dried beans in sealed jars in a cool, dry cupboard.
A kitchen shelf above the stove or beside a sunny window is warmer than it looks, so a cooler inside cupboard or pantry is a better choice. Beans should be fully dry before going into a jar, since damp beans in a sealed jar can mold. A label with the harvest year helps you use the oldest jar first.
Use stored beans within a year for best texture. Soaking old beans longer before boiling may help, though truly hard-to-cook beans may never fully soften. Save the plumpest dry seeds for next year’s planting.