When to Harvest Peanuts? Peanut Profile Chart and Beyond
Deciding when to harvest peanuts is one of the biggest challenges facing peanut growers each year. New methods are available to farmers helping them to optimize peanut yields.
Peanuts plants are indeterminate in fruiting. This means that they continue to flower, peg, and produce peanuts over an extended period of time, as environmental conditions allow. As harvest nears, each plant has grown about 40-50 pods, across a wide range of maturity.
When are the peanuts ready to harvest? The farmer must know the peanuts' maturity when deciding the best time to harvest for maximum yield. This is not trivial.
Peanuts grow underground making it impossible to determine their maturity without digging them. Other legumes allow direct observation of their development, because they grow above ground.
Peanut growers are only able to assess crop maturity by digging samples from the field. The peanut profile chart helps reveal the distribution of the pods' maturity, and helps the farmer to decide when to harvest a specific peanut field.
A pressure washer is first used to prepare the peanuts by stripping off the cork like outer layer of the hulls. Immature peanuts have white inner husks. As peanuts age their husk color changes to yellow, then orange, then brown, and finally black. The overall distribution of husk colors is revealed by placing power-washed samples of peanuts on the peanut profile chart.
Each 2 columns of the peanut profile chart represent about one week of growth. The peanut profile chart also reveals 'split crops' where peanut maturity is not in a normal distribution due to drought or other environmental factors.
Tracking Lifetime Growth Temperture Helps in Deciding When to Harvest Peanuts
For more than 30 years the 'peanut profile chart' or 'peanut profile board' has been a helpful tool for deciding when to harvest peanuts, but more accurate ways of predicting harvest time are needed. Peanut researchers are investigating additional ways to decide when to harvest peanuts for maximum yield.
Some peanut strains maturity rate don't fit the peanut profile chart.
Another method of deciding when to harvest peanuts was borrowed from cotton farmers. The growing degree day method (called DD-60 for cotton) uses temperature tracking during crop development to determine harvest time for optimal yield. When applied to peanuts it is called DD-56 which is calculated by averaging the daily maximum and minimum temperatures, and subtracting 56.
Adding the daily DD-56 computes the heat unit for a given period of time. The total number of growing degree days is one indicator of crop maturity.
Hollis quotes Wilson Faircloth, research agronomist with the National Peanut Research Laboratory in Dawson, Ga. "The important part of this is that you have to add in the water. It doesn't take just heat to mature a peanut, it also takes water, and you must have both together. It's a pretty good tool for determining peanut maturity. This method was evaluated last year, and every variety tested peaked at 2,500 growing degree days, plus or minus eight to 10 growing degree days.
In July or August when daytime temperatures are in excess of 95 degrees F. and low temperatures at night are in the 70s a peanut plant can accumulate about 15 growing degree days per day.
Some peanuts put on 30 percent of their growth in the last two to three weeks of the season; that's huge."