Understanding barley growth and development is essential for profitable production.
This is because many of today’s agricultural chemicals must be applied at critical times, which means producers must recognize barley growth stages.
By using physiological maturity indicators, you can make harvest decisions that will maximize crop yield potential.
How barley develops
Barley (Hordeum vulgare L.) originated in the Eastern Mediterranean region.
Head type and growth habits
You can distinguish barley by differences in head type and growth habits. In a six-rowed barley, three kernels form at each node of the head, while in a two-rowed type, only a single kernel forms at each node (Figure 1).
Barley is also classed by its requirement for cold temperatures. Winter barley seedlings must be exposed to cold temperatures (vernalization), which enables it to normally produce heads and grain later.
Winter barley is usually sown in the fall for exposure to low temperatures during the winter. It then completes development the following spring and summer. Spring barley doesn’t require exposure to winter temperatures and can be sown in spring. Winter types usually mature somewhat earlier than spring types.
Here, we’ll consider the growth and development of the six-rowed spring barley commonly grown in Minnesota.
Figure 2 shows major developmental stages in spring barley with the approximate time and heat units required to reach each stage. Differences in maturity exist among varieties. For simplicity, Figure 2 does not show tillers beyond the advanced tillering stage.
Barley production has become more intense and complex. Crop managers must understand barley development and be able to recognize growth stages because of the increased use of growth-stage-sensitive production inputs such as chemical fertilizers, pesticides and growth regulators.
Growth staging systems
A number of staging systems have evolved for describing the development of cereal crops such as barley.
We describe the Zadoks system, which is the most comprehensive and may be the most helpful guide when making management decisions. In addition, we introduce the Haun and Feekes-Large staging systems.
The Zadoks system is becoming the most universally accepted. It’s applicable to any small grain, and its stages are easy to identify in the field.
The two-digit code system
The Zadoks system is a two-digit code. The first digit refers to the principal stage of development beginning with germination and ending with kernel ripening. Table 1 gives the nine principal growth stages.
The second digit (also between 0 and 9) subdivides each principal growth stage. A second digit value of 5 usually indicates the midpoint of that stage. For example, a 75 refers to the medium milk stage of kernel development.
In seedling growth (principal growth stage 1), the second digit refers to the number of emerged leaves.
To be counted, a leaf must be at least 50 percent emerged. A code of 13 indicates that three leaves on the main shoot are at least 50 percent emerged. Tiller leaves are not counted.
To time herbicide applications, the seedling stage (stage 1) identifying the leaf numbers is useful.
For tillering (principal stage 2), the second digit indicates the number of emerged tillers present on the plant.
Because stages may overlap, it’s possible to combine Zadoks indexes to provide a more complete description of a plant's appearance. For example, a plant with one tiller and three leaves could be described by either or both of the Zadoks stages 13 and 21.
As the plant matures, the Zadoks stages describing kernel development are usually used alone.
The Haun system mainly concerns the leaf production stages of development.
The length of each emerging leaf is expressed as a fraction of the length of the preceding fully emerged leaf. A 3.2 indicates three leaves are fully emerged, and a fourth leaf has emerged two-tenths of the length of the third.
Although this system can be modified, it’s not as useful when making decisions using developmental indicators other than leaf numbers. Yet, agronomists and weed scientists concerned with seedling development staging and particularly leaf numbers may find the system useful.
The Feekes-Large system has been widely used, but is becoming less popular.
It numerically identifies stages such as tillering, jointing and ripening, but lacks the more detailed attributes of the Zadoks and Haun systems.
Table 1: Condensed summary of the Zadoks two-digit code system for growth staging in barley with corresponding Feekes scale
|Zadoks code: Principal stage||Zadoks code: Secondary stage||Description||Corresponding Feekes code|
|1||Start of imbibition (water absorption)|
|9||Leaf just at coleoptile tip|
|0||First leaf through coleoptile|
|1||First leaf at least 50 percent emerged|
|2||Second leaf at least 50 percent emerged|
|3||Third leaf at least 50 percent emerged|
|4||4 Fourth leaf at least 50 percent emerged|
|5||Fifth leaf at least 50 percent emerged|
|0||Main shoot only|
|1||Main shoot plus one tiller visible||2|
|2||Main shoot plus two tillers|
|3||Main shoot plus three tillers|
|4||Main shoot plus four tillers|
|5||Main shoot plus five tillers||3|
|1||First node detectable||6|
|2||Second node detectable||7|
|3||Third node detectable|
|7||Flag leaf just visible||8|
|9||Flag leaf collar just visible||9|
|1||Flag leaf sheath extending|
|3||Boot just beginning to swell|
|7||Flag leaf sheath opening|
|9||First awns visible|
|1||First spikelet of head just visible||10.1|
|3||One-fourth of head emerged||10.2|
|5||Half of head emerged||10.3|
|7||Three-fourths of head emerged||10.4|
|9||Head emergence complete||10.5|
|6||Flowering (not readily visible in barley)|
|1||Beginning of flowering||10.5.1|
|5||Half of florets have flowered||10.5.2|
|7||Milk development in kernel|
|1||Kernel watery ripe||10.5.4|
|8||Dough development in kernel|
|7||Hard dough, head losing green color|
|9||Approximate physiological maturity|
|1||Kernel hard (difficult to divide with thumbnail)||11.3|
|2||Thumbnail cannot dent kernel, harvest ripe||11.4|
Growth and development
Barley’s growth cycle has the following divisions: Germination, seedling establishment and leaf production, tillering, stem elongation, pollination and kernel development and maturity.
The minimum temperature for barley germination is 34 to 36 degrees Fahrenheit (1 to 2 degrees Celsius).
After the seed takes up moisture, the primary root (radicle) emerges. The radicle grows downward, providing anchorage and absorbing water and nutrients, and eventually develops lateral branches.
Other roots formed at the seed level make up the seminal root system (Figure 3). These roots become highly branched and remain active throughout the growing season.
After the radicle emerges from the seed, the first main shoot leaf emerges. It’s enclosed within the coleoptile for protection as it penetrates the soil. As a result, the seeding depth should not exceed the length the coleoptile can grow, usually no more than 3 inches (7.6 centimeters).
Once the seedling emerges, the coleoptile stops elongating and the first true leaf appears (Figure 4). Then leaves appear about every three to five days depending on the variety and conditions.
Figure 5 shows a seedling at the two-leaf stage.
Growing degree units
Another way to quantify leaf appearance is in terms of accumulated heat units. Calculate heat units by summing the number of degrees above 40 degrees Fahrenheit for each day. Use the following equation to calculate heat units for each day:
Growing degree unit =[ (maximum temperature + minimum temperature) / 2] - 40 degrees F
About 100 heat units accumulate between the appearance of successive leaves in a medium maturing barley (Figure 6). Eight or nine leaves usually form on the main stem, with later maturing varieties usually forming more leaves.
Emergence of the final leaf, termed the flag leaf, is an important growth stage for timing the application of certain growth regulators (Figure 7).
When the seedling has about three leaves, tillers usually begin to emerge.
Barley plants’ ability to tiller is an important method of adapting to changing environmental conditions. When environmental conditions are favorable or if plant density reduces, it’s possible to compensate for this by producing more tillers.
When and how spring barley tillers
Under typical cultural conditions for spring barley, tillers emerge during about a two-week span with the total number formed depending on the variety and environmental conditions (Figure 8).
Deep seeding and high seeding rates usually decrease the number of tillers formed per plant. More tillers may form with low early season temperatures, low plant populations or high soil nitrogen levels. Some tillers initiate roots, contributing to the nodal root system.
About four weeks after crop emergence, some of the previously formed tillers begin to die without forming a head (Figure 9).
The extent that premature tiller death occurs varies depending on the environmental conditions and variety. Under poor or stressed growing conditions, plants respond by forming fewer tillers or by displaying more premature tiller death.
Until jointing, the plant apex or growing point is below the soil surface where it’s somewhat protected from frost, hail or other mechanical damage.
Between three and four weeks after plant emergence, the stem’s upper internodes begin to elongate, moving the growing point above the soil surface. The head also begins to rapidly grow, although it’s still too small to readily detect through the surrounding leaf sheaths.
During the “boot” stage, the head becomes prominent within the flag leaf sheath (Figure 10).
Pollination usually takes place in barley just before or during head emergence from the boot. Pollination begins in the head’s central portion and proceeds toward the tip and base.
This event occurs six to seven weeks after crop emergence. Because pollen formation is sensitive to stress, water deficits and high temperatures at this time will decrease the number of kernels that form and may reduce yields.
You can diminish these yield reductions by planting early so pollination and early grain filling is completed before late-season stresses occur.
Once head emergence and pollination have occurred, kernels begin to develop (Figure 11). The length of the barley kernel establishes first, followed by its width. This helps explain why thin barley developed under stress conditions is usually as long as normal grain, but is narrower.
Figure 11 shows the physical changes as a kernel develops.
Watery ripe and milk stages
The first period of kernel development, designated the “watery ripe” and “milk” stages, lasts about 10 days.
Although the kernels don’t gain much weight during this phase, it’s extremely important because it determines the number of cells that will subsequently be used for storing starch. Kernels crushed in this stage initially yield a watery substance that later becomes milky.
Soft dough stage
The “soft dough” stage is characterized by kernels with a white semi-solid consistency. This period of rapid kernel growth and starch storage usually lasts about 10 days following the milk stage.
Hard dough stage
Finally, as the kernel approaches maturity and begins rapidly losing water, its consistency becomes more solid, termed “hard dough.” This is when the kernel also loses its green color (Figure 11).
When kernel moisture has decreased to about 30 to 40 percent, it has reached physiological maturity and will not accumulate additional dry matter. Figure 11d shows a harvest ripe kernel with lemma and palea attached. At this time, the final yield potential has been established.
An easily identifiable field indicator of physiological maturity is 100 percent loss of green color from the glumes and peduncle. (Figure 12).
Although the grain’s moisture content is still too high for direct combining, it can be swathed and windrowed. When kernel moisture decreases to 13 to 14 percent, the barley kernel is ready for combining and threshing.
Factors affecting leaf area establishment
Because photosynthesis provides energy for growth and dry matter for yield, it’s important that leaf area be rapidly established and protected throughout the growing season.
Early in the plant’s growth, the leaf blades are the major photosynthetic organs. The rate of leaf area establishment depends on temperature, but can be increased by high nitrogen fertilization and seeding rates.
Duration and impact on yield
The duration of leaf function is also important for maximum grain yield. The maximum leaf area is usually reached about heading, then declines during grain growth when the demand is great for photosynthate (products of photosynthesis).
As the lower leaves die, the upper leaf blades, leaf sheaths and heads become very important as photosynthetic sources for grain filling. For maximum yields, the last two leaf blades and sheaths, as well as the head and awns, are particularly important.
Barley also has a limited capacity to mobilize substances that were produced and stored earlier in the growing season, if conditions reduce the capacity of the plants to produce current photosynthate.
Anther: The part of the flower that produces the pollen.
Coleoptile: The sheath that encloses the first main shoot leaf and provides protection as it emerges from the soil.
Flag leaf: The leaf immediately below the head.
Floret: An individual flower within the head.
Glumes: The pair of bracts located at the base of a spikelet in the head.
Internode: The part of a stem between two nodes.
Jointing: Stage of barley development when stem nodes are first detected above the soil; Zadoks stage 31.
Leaf blade: The flattened portion of a leaf above the sheath.
Leaf sheath: The lower part of a leaf enclosing the stem.
Lemma and palea: Bracts (hulls) enclosing the kernel. After threshing, the lemma and palea usually adhere to the kernels.
Main shoot: The primary shoot which emerges first from the soil and from which tillers originate.
Node (Joint): A region on the stem where leaves are attached.
Peduncle: The top section of the stem between the flag leaf and the head.
Seminal roots: Roots arising at the level of the seed.
Spikelet: The flower of a grass consisting of a pair of glumes and one or more enclosed florets.
Tiller: A shoot originating from the base of the plant.
Bauer, A., Eberlein, C.V., Enz, J.W. & Fanning, C. (1984). Use of growing-degree days to determine spring wheat growth stages. North Dakota State University Extension Bulletin, 37.
Haun, J.R. (1973). Visual quantification of wheat development. Agronomy Journal, 65, 116-119.
Large, E.C. (1954). Growth stages in cereals, illustration of the Feekes scale. Plant Pathology, 3, 128-129.
Bongard, P.M. Oelke, E.A., & Simmons, S.R. (2018). Spring wheat growth and development guide.
Chang, T.T., Konzak, C.F. & Zadoks, J.C. (1974). A decimal code for the growth stages of cereals. Weed Research, 14, 415-421. https://doi.org/10.1111/j.1365-3180.1974.tb01084.x
Reviewed in 2018