Recently we got a call about butterbeans (Phaseolus lunatus). Our client stated he was “having a hard time getting them to come up. How deep should they be planted?” He did mention that the plants were experiencing blossom drop and that the yields had diminished over the past two years. He wanted more information about butterbeans and wanted to know what to do.
DIAGNOSIS / RECOMMENDATION:
After further conversation with the gentleman, the Master Gardener on duty determined that, amongst other things, he had planted butterbeans in the same spot for several years. The log sheet gives no indication whether the client had ever amended the soil or provided any irrigation.
The following recommendations were provided to the client:
- Move locations of plantings in garden some next year
- Planting depth – 1” to 2″
- If soil tends to get water-logged, dig up to 12″ and incorporate compost
- Blossom drop can be due to weather conditions, specifically excessively hot/dry OR cool/wet conditions.
Beans, in general, do best in sunny locations, and planted in warm (65 to 80oF), welldrained, deep sandy loam, with a pH level between 5.8 to 7.0. The exception to this are fava beans which prefer cooler soil temperatures (60 to 65oF). 
Butterbeans, aka sieva beans, Burma beans, Madagascar beans, Carolina beans, and “baby limas,” are small-seeded lima beans and are usually bush type (as opposed to pole) beans. 
The soil temperature must be a minimum of 65oF for five days for these beans to germinate. Soil should be kept moist (but not soaking wet) until the seedlings come through the ground. Prevent crusting by spreading . inch of sand, sawdust, or a light mulch over the seeded row.
Many vegetables are susceptible to blossom drop due to either hot / dry OR cool/wet weather conditions, or inconsistent or lack of moisture in the soil. However, baby lima or butterbeans are less susceptible to blossom drop problems. 
Pests: lima beans are susceptible to attack from aphids, corn earworm, grasshopper, Mexican bean beetle, spider mite, stink bug, and thrips.
Diseases: lima beans are susceptible to anthracnose, bacterial blights, Botrytis blight (Gray mold), downy mildew, powdery mildew, Rhizoctonia root and stem rot, rust, seed rot and damping off, and viruses. 
Small-seeded limas generally are ready for harvest from 60 to 80 days from sowing. For a continuous harvest throughout the growing season, plant succession crop bush butterbeans every two weeks. Be mindful that these beans will not set pods in temperatures above 80oF or in cold or wet weather.
As always, when in doubt about the condition of the soil, a soil sample should be taken, sent to VT for analysis, and then follow the recommendations contained in the analysis before planting.
More information about beans, in general, and limas, specifically can be found at the Reference or Additional Information links below.
From The Bedford Extension MG Help Desk
Linda E., Bedford Extension Master Gardener Volunteer; Help Desk Coordinator
SOURCE: Butterbean Basics
ADDITIONAL INFORMATION LINKS:
All resource links accessed April 19, 2017
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Answers provided herein were based on specific situations and growing conditions.These recommendations may or may not be appropriate for all circumstances.For specific recommendations for your particular situation please contact your local Cooperative Extension Office.
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–A Bedford Area Master Gardeners Association (BAMGA) Publication–