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How Late Can Perennial Forages Be Planted?

How Late Can Perennial Forages Be Planted?

By Justin Brackenrich

Spring is a traditional and popular time in Pennsylvania to plant forages. However, wet soil conditions and unpredictable weather often make this practice difficult. Many growers then ask the question, "When is too late to plant" or "If I can't plant my cool-season forages this spring, what can I do?"

When is too Late to Plant?

This answer is very dependent on the weather as we move into the heat of summer. What we can rely on is what we know about how cool-season forages establish. Cool-season grasses will begin to grow when soil temperatures reach 40-45°F, reach their optimum growth when temperatures are between 60 and 75°F, and decline in growth as temperatures continue to increase in the summer months. Cooler night temperatures can help with growth on hotter days, but eventually, cool-season grasses will go dormant until the fall when temperatures begin to recede.

To start answering the question "When is too late to plant?" we will need to make a couple of assumptions,

  • First- we will get adequate moisture; not too much or too little, but just the right amount for germination and initial growth. 
  • Second- the temperatures will remain consistent with the state averages and not be unseasonably warm or cool.
  • Third- day time temperatures above 75°F can be tolerated if the lows are less than 60°F.
  • Fourth- stands will be established a minimum of six weeks before the temperatures outlined in assumption three are reached, sending the stands into summer dormancy.

Yes, there are a lot of things working against us, but this is what can make spring seedings so challenging.

State weather data tells us that certain parts of the state will have different cut off dates. Historical weather data shows the average date that highs are greater than 75°, and lows are greater than 60°. See Table 1. What this climate data shows is that for some areas of the state it is safe to plant until mid-May, while late April represents the closing date for others.

Table 1. Ideal Growing Temperatures for Cool-Season Grasses in Pennsylvania

LocationFirst Day of 75° High and >60° LowLast Day of Safe Planting
ErieJune 19May 8
WilliamsportJune 22May 11
PittsburghJune 19May 8
AllentownJune 18May 7
ScrantonJune 28May 17
PhiladelphiaJune 2April 21
HarrisburgJune 7April 26

Information from the PA State Climatologist

This should not be used to make all your decisions, or by any means is this saying "anything after this date will fail" but it is evident that after these dates the risk associated with these plantings does increase.

What to do if you can't spring plant?

Since this is a spring seeded forage, the expectation should be low for getting more than one cut toward the end of the growing season. Meaning yield loss may be more evident in the next growing season when attempting to get multiple cuttings. However, if hay or pasture will be in short supply without this planting, use a summer annual, like sorghum-sudangrass or millet, followed by a fall seeded cool-season perennial to reduce a forage shortage this summer. Planting a cool-season perennial in late summer or fall will allow the stand more time to catch up, and return to productivity, rather than waiting for the subsequent spring to try again.

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