Articles

When to Switch Corn Relative Maturity?

Knowing when to switch from a longer maturity to a shorter maturity corn hybrid is a big decision and one that takes time and consideration.

Save for later Print

Updated:

June 3, 2025

Skip to the end of the images gallery

Corn planting has taken longer than expected in 2025. Image Credit, A. Frankenfield, Penn State Extension

Skip to the beginning of the images gallery

If you are in the same boat as many other producers and haven't planted all, or any, of your corn, you may be thinking about options for switching some of your longer 105 to 115-day RM to something a little shorter. However, you may not know when to make this decision or how much shorter to go. There are some resources and estimates that we can use to help us make these decisions.

Understanding Options

Start by looking at the growing degree day possibilities for your area. There are many options for tools, apps, and calculators, but for this article, we will use the Climate Smart Farming Growing Degree Calculator from Cornell University. Growing degree days, or GDD, are measurements of heat used to estimate how crops move through their physiological cycles. For more on GDDs, read Understanding Growing Degree Days.

This is a screen capture of the Climate Smart GDD Calculator interface. First, begin by selecting the earliest possible planting date and GDD base for your area. I have selected April 15 and base 50. Notice the plateau of the accumulations. In Masontown, PA, historically, GDD accumulation slows around October 15, which will be important to know for grain drying. Working backwards, corn hybrids typically need about 300-400 GDDs to transition from maturity, or black layer, to a harvestable moisture. If accumulation slows on October 15, at 3,037 GDD, our maturity date should be around September 13, or 2,682 GDDs.
Next, determine how many GDDs have been missed this year. As of June 1, 423 GDDs. By subtracting the current accumulated GDDs from the 2,682 GDDs from our estimated black layer date, we have an estimated 2,259 units remaining for the season.
Before deciding, always know your production costs before planting any crops outside the normal planting times. Understanding your inputs, insurance options, current and projected market, and estimated yield should all be considered. Agronomy Guide Table 1.4-8, Part A, B, and C (see below) provides estimated yields for various planting dates.
Comparing the calculated remaining GDDs of 2,259 to the table below, we can determine what remaining maturities are appropriate for our areas. For this example, hybrids in the range of 110-day are still an option (see things to consider).

Table 1. Approximate relative maturities and needed growing degree days to reach maturity
Approximate Relative Maturity Rating	Growing Degree Days Needed for Maturity
90-95	1,600 – 1,824
96-100	1,825 – 2,024
101-105	2,025 – 2,350
106-110	2,350 – 2,499
111-115	2,500 – 2,724
>115	2,725 - beyond

Things to Consider:

Later planting corn will reduce GGD needs. A study by Neilson et. In 2002, in Indiana and Ohio, researchers found that needs can reduce as much as 4.5 and 3.2 GDD per day for late and early maturities, respectively.This does not mean that you can plant 120-day corn in the northern tier of Pennsylvania on June 15 and make grain, but it does mean that there is some flexibility. Other studies have also found that in Pennsylvania, most corn hybrids mature approximately 200 GDDs shorter than what is reported from midwestern trials.
If going to the trouble to swap out your longer maturity corn with something shorter, and you aren't fully sure when your planter will return to the field, mid-Atlantic seedsmen are recommending seeking corn that is 7 to 10 days shorter relative maturity than what you wish to exchange. Be careful not to make too drastic changes in your RM. Although a drastic reduction will lead to drier grain and reduced drying costs, it will not be more profitable than a fuller season corn that may need a little drying.
Seed companies in Pennsylvania try to have a surplus of shorter RM corn available when changing is necessary, often having an extra 20% of each maturity group in reserve. This means that it is usually possible to change your maturity, but you should consult your seed company for availability. An informal poll of several seed corn dealers in central PA indicates that there is a fair amount of shorter-maturity corn yet available for 2025.
After June 15, for most of PA, especially if the corn is intended for grain harvest, consider changing to alternative crops. If you are already growing soybeans, increasing your soybean acres may be a good option as they provide more planting flexibility. If you are raising your corn for feed, and sub-90-day corn is unavailable, consider an alternative forage option like sorghum/sudangrass. With any change to species, you need to consider fertilizer and herbicide practices.

Tables 1.4-8 A, B, and C. Estimated grain yields for various planting dates and population rates.

Part A. Optimum Yield (as percent). Figures shown are most applicable to fields with less than 125 bushels per acre.
Planting Date	Plants/acre at Harvest 12,000	Plants/acre at Harvest 14,000	Plants/acre at Harvest 16,000	Plants/acre at Harvest 18,000	Plants/acre at Harvest 20,000	Plants/acre at Harvest 22,500	Plants/acre at Harvest 25,000
April 20	72	78	83	87	90	93	95
April 25	75	81	86	90	93	96	98
May 1	77	83	88	92	95	98	100
May 6	78	83	88	92	95	98	100
May 11	77	83	88	92	95	98	99
May 16	75	81	86	90	93	96	98
May 21	73	78	83	87	91	94	95
May 26	69	75	80	84	87	90	92
May 31	64	70	75	79	82	85	87
June 5	59	64	69	73	77	80	81
June 10	52	58	63	67	70	73	75

Part B. Optimum Yield (as percent). Figures shown are most applicable to corn fields with yields between 125 and 175 bushels per acre.
Planting Date	Plants/acre at Harvest 10,000	Plants/acre at Harvest 12,500	Plants/acre at Harvest 15,000	Plants/acre at Harvest 17,500	Plants/acre at Harvest 20,000	Plants/acre at Harvest 22,500	Plants/acre at Harvest 25,000	Plants/acre at Harvest 27,500	Plants/acre at Harvest 30,000
April 10	62	70	76	82	86	90	92	94	94
April 15	65	73	79	84	89	92	95	97	97
April 20	67	74	81	86	91	94	97	98	99
April 25	68	75	82	87	92	95	98	99	100
April 30	68	75	82	87	92	95	98	99	100
May 4	67	75	81	86	91	94	97	99	99
May 9	65	73	79	85	89	93	95	97	97
May 14	63	70	76	82	86	90	92	94	95
May 19	59	66	73	78	83	86	89	90	91
May 24	54	62	68	74	78	82	84	86	86
May 29	49	56	63	68	73	76	79	80	81
June 4	43	49	57	63	67	70	73	75	75
June 9	36	42	49	56	60	62	65	67	68

table c

Part C. Optimum Yield (as percent). Figures shown are most applicable to corn fields with yields greater than 175 bushels per acre.
Planting Date	10,000	15,000	20,000	25,000	30,000	35,000	40,000
April 1	54	68	78	88	95	99	99
April 10	57	70	81	91	97	100	100
April 20	58	71	81	91	97	100	99
April 30	58	70	80	89	95	97	96
May 9	55	68	77	86	91	93	91
May 19	50	63	72	80	85	86	94
May 29	44	56	65	73	77	78	75
June 8	35	47	56	63	67	67	64