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As the winter season slows to an end and spring comes into full swing, cover crops might not have grown as expected. From stunted growth, late blooming, to dead in the field, there are a variety of reasons why a cover crop might have failed. In this article, we’ll be discussing the most common causes and what can be done about them.

Cover crop performance can be affected by numerous factors throughout their growth. Common ones include issues with planting, flood or drought, improper plant selection, soil conditions, weed competition and expectations.

Planting and Water Management
There is a lot of planning and preparation that goes into planting a cover crop. The seeder needs to be calibrated, the soil may need to be prepped, and, if using a broadcaster, the seed should be incorporated. Machines can break and slow down planting or place seed incorrectly. In the case of drop seeders and seed drills, an emitter can become plugged and leave strips unplanted. If a broadcaster is used and the seed isn’t incorporated, usually by dragging something over the soil, such as a piece of chain-link fence or harrow, germination rates can be reduced, especially for large seeds.

Planting too late in the season can also affect performance. Once soil temperatures begin to drop, germination is slowed or halted. In most cases, the Seeds for Bees program does not recommend planting after late November. It is better to save the seed and wait to plant in the spring or following fall.

Another issue that can arise after planting is water. In some seasons, early winter rains can sprout the seeds. However, should this be followed by an extended dry spell, these seedlings can wither and die. On the other hand, too much water, especially standing water, can suffocate and drown seedlings and even established plants. Standing water limits a plant’s access to oxygen, which is taken up through the roots of most terrestrial species. During dormancy, oxygen requirements are reduced, which is why a cover crop may perish in a flooded orchard while the trees survive.

Not enough water shortly after planting the cover crop can also reduce its performance. Water is not only a requirement for life and growth; water absorption is a required signal to germinate. If a cover crop is planted and not followed up with enough water from an irrigation or rain event, it may not sprout. This can delay cover crop establishment and create an irregular stand. It can be advantageous to plant a cover crop before the final post-harvest irrigation in orchards.

Selection and Soil Conditions
Cover crop mixes should be designed around the needs of the farm and site conditions. However, there are times when the best planning can go astray. If the wrong cover crop is selected, plants can fail where others would have thrived. For instance, planting barley in a soil that is often cold and soggy in the winter will result in dead or stunted plants, where planting triticale in the same location would have provided better growth.

Keep in mind that human error is bound to occur from time to time. Sometimes bags can be mislabeled, the wrong seed gets mixed, or orders can get scrambled. Though this is rare, it’s good to pay attention and inspect your order promptly, double-checking with the seed supplier if the seed doesn’t look as expected.

Soil conditions are the basis of farming. Though most farmed soils in California will not be particularly bad, factors such as pH, salts, compaction, crusting and nutrient content should be considered when selecting a mix. A cover crop that is not suited for the conditions it is planted in is bound to perform poorly. For instance, a low-nitrogen soil might yield a stunted cover crop unless a leguminous cover crop is selected. Compacted soils would be better suited for more aggressive species, such as brassicas.

Soil crusting is particularly tough on seeds and seedlings. In soils where crusting or compaction has been an issue, try planting and irrigating the cover crop before heavy rains. If the plants are up before crusting can occur, then they are better suited to survive the rain event and can even protect the soil from further crusting, depending on their size and density.

Weeds and Expectations
Weed competition can prove damaging for a young or less competitive cover crop. Young plants can be choked out by more established plants and weaker species can be overtaken by swifter plants. Controlling weeds before planting is often the best course of action. Planting with a vigorous mix before resident vegetation starts growing is often the best option. There is very little that can sprout before grasses in the fall, though another grass or brassicas can be a good choice.

When considering cover crops, be sure you are clear on your growing conditions and goals when communicating with your seed selection advisor. Miscommunication can lead to unmet expectations, and a cover crop that has not met the requirements for which it was planted has failed.

‘A cover crop that has not met the requirements for which it was planted has failed.’

A final factor that can affect growers’ expectations is yearly variations in cover crop growth. The cover crop’s growth potential can be affected by a variety of year-to-year changes. Aspects such as when the rainy season begins, average winter temperatures, sunny or foggy conditions, and what all else the weather may do can boost or restrict cover crop growth. Understanding that a cover crop can grow differently despite planting the same cover crop year over year can help with managing expectations. In the case of reduced growth due to weather conditions, the cover crop can be allowed to grow longer than previously planned to achieve the goals for which it was planted. However, this extended growth period should not be allowed to interfere with other farm operations.

For growers located in California who would like to give cover crops a try, or retry, the Seeds for Bees program will be open for applications from April 1 to Aug. 31. The application is short, taking approximately 10 minutes to complete, and doesn’t require any additional paperwork. To sign up, go to Project Apis m.’s webpage and navigate to the Seeds for Bees tab to find the application. Applicants are accepted on a first-come, first-served basis after they meet program requirements.