Pasture & Range: September 2003

One of the most challenging and frustrating problems agricultural producers face is to figure out what happened to a planted crop that failed to come up. This is especially true if the person who planted the crop apparently did everything right! A review of the process of germination can help explain some of the things that could go wrong before seed is purchased or after it is placed in the ground.

A simple definition of germination is when the embryo inside of a seed absorbs water, resumes growth and the radicle (embryonic root) emerges through the seed coat and begins to grow. To grow, a seed must contain a live, fertilized embryo. Unfortunately, you cannot tell this by looking at the outside of the seed. This is why it is time and money well spent to purchase seed with a germination test or otherwise obtain a germination test. Now, let's throw a twist in here: A seed may be alive (viable) but unable to germinate and grow. This can be due to conditions either internal or external of the seed.

An internal condition can be one in which the embryo has not reached a maturity point capable of germination due to chemical inhibition or the seed coat is so hard (hard seed) that it impedes the absorption of water and oxygen preventing the resumption of growth. By either means, the seed is then referred to as being dormant. Dormancy can be viewed as a safety mechanism to prevent germination when conditions are not favorable for seedling survival. During a germination test, dormancy can be broken and seeds forced to germinate. While this will give you an accurate estimation of potential germination, a high presence of dormant seed at planting can still result in stand failure because all the seeds will not germinate at the same time.

Dormancy due to a hard seed coat is important to the persistence of some forage crops such as arrowleaf clover, an annual with a high percentage of hard seed that gives it good re-seeding potential. Crimson clover does not have a high percentage of hard seed, so seeds often germinate shortly after seed drop, limiting its reseeding ability. Dormancy is a liability to producers wanting to establish eastern gamagrass. After planting, we want it all to come up at once. To increase germination, gamagrass seed must go through some type of scarification to soften the seed coat. What is the take-home point to this? Dormancy will influence seed germination of some forage crops — it should be accounted for and adjustments made for it prior to seeding. Depending on the seed, it might require chilling, chemical treatment or time to break dormancy and increase germination. Figure 1 is a table of various plant species with some of their known seed life spans. Some of these seed life spans are rather amazing!

External conditions that limit germination can often be prevented. The most common external barriers are soil related and at least one is sometimes neighbor influenced. Planting when soil temperatures are not optimal for germination can be corrected by knowing what soil temperatures are required for a particular seed to germinate — they are not all the same. Results can be a thin stand or stand failure. This happened this year with crabgrass planted too early prior to warm soil temperatures. It resulted in several phone calls to the Foundation this spring from anxious producers wanting to know what happened. This can often be neighbor influenced and is easily corrected by purchasing yourself a set of blinders to focus your attention on what the soil is doing and not what your neighbor is doing.

Planting seed too deep is another common reason for germination failure and is easily corrected. Generally the larger the seed, the deeper it can be planted, but the majority of grass and legume seed will only be planted at a depth of 1/4 to 1/2". Sometimes this may be adjusted slightly to compensate for the amount of moisture in the soil. Seeding depth guides are available from numerous sources, take a look at one then go and dig up a few seeds during the planting process to make sure depth is correct.

One thing we can't do a lot about is the weather. Cloudy days can influence soil temperatures and moisture. Lack of soil moisture can be compensated for with irrigation but if you don't have that, all you can do is wait. One thing is for sure: If conditions are right, plant! If moisture is a limiting factor to seed germination when the rain comes, seeds still won't come up if they are not in the ground.