Soil Temps and Grass Growth – What’s happening now?

In his latest issue of Grazing Bites, Victor Shelton paused to think about a question someone asked him:

“Don’t you think that the grass seems greener after the snow melted away and is it growing?”

Victor’s answer was, “It might still feel rather cool to most people, but it doesn’t take much warmth, especially in soil temperature, to initiate some growth for cool season grasses. Soil temperatures much above freezing, especially with some warm sunny days and increasing daylight, can entice new growth.  Soil temperatures above 50 degrees really promotes growth.”

What Victor is talking about are cool season grasses: various wheatgrass, needlegrass, bromes, bluegrass, orchardgrass and fescue. These grasses begin growth in early spring when soil temperatures maintain 40-45 degrees F (7 C) and daytime temperatures are warm enough for growth. Cool season grasses are known for producing high-quality forage with high levels of crude protein early in the growing season. But once temperatures rise above about 75 degrees (23 C) they often become semi-dormant.

But don’t let the cows out yet! As Victor points out, “Just because we have some new growth coming on in the pastures does not mean to let the livestock have at it. We are a good way from that yet. Grazing too early in the spring does nothing but remove some of that solar panel the plants need to start rebuilding sugar and growing new roots. The forages really need to be able to canopy over and get a good start before livestock start removing that top canopy or production will be reduced.”

How do you know when it’s time to graze?

The leaf stage, or the number of leaves on a plant’s tiller, is a good indicator of when the plant has enough leaf area to tolerate grazing. To find what leaf stage your grasses are in, pluck a stem at ground level and count the mature leaves. these are leave that are “collared” – the leaf blade goes all the way around the stem like a collar on a shirt.

These photos from Bethany Johnston, Nebraska Extension Educator give you an idea of what you’re looking for.

This grass is in the two-leaf stage and close to the three-leaf stage. The upright leaf is immature and hasn’t quite formed a collar.

Here’s another example of a plant in a two-leaf stage:

Finally, here’s a grass in a three-leaf stage:

When your grass plants have reached the three-leaf stage you can begin grazing. If you graze before they reach this stage, they won’t have enough leaf area (solar collector) to be able to regrow from photosynthesis alone. Instead, they’ll use root reserves. This makes them less resilient and slows regrowth, so you’ll have to wait longer before you can return to that pasture.

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