The Best Time to Plant Alfalfa

In the San Joaquin Valley it is possible to establish a stand of alfalfain any month of the year, but there is a time to plant which will resultin a stand that is longer lasting and more productive than any other. Thekey is to plant the hay at the time which will be most conducive to theformation of a good root system which will carry the plant throughout thelife of the stand.

Dr. Larry Teuber at UC Davis did studies under controlled conditionsthat showed that seedling alfalfa roots grow best at 2 inch average soiltemperatures 69 to 76oF. These temperatures occur in mid-September to earlyOctober and again from late April to early May. However, his studies alsoshowed that at temperatures above 68oF the young alfalfa plant sends moreof its energy into making top growth than root growth, and below 68oF willsend more energy into making roots. Consequently, planting in early fallwill not only give the optimum temperatures the plant needs to grow butmore of that growth will be directed at developing a good root system.

Day length also has an effect on the proportion of roots to top growth.As the days become shorter than 12 hours of light, root growth is stimulated,but tops are stimulated when the days are over 12 hours long.

Both day length and temperature then point to an early fall (last twoweeks in September to first week in October) planting date as being idealfor the formation of a strong root system. This laboratory prediction isbourn out by studies conducted in the late '70's which compared yieldsof spring and fall planted alfalfa.

During the first season in a study planted in 1976, the yields for thefirst cutting season showed a yield advantage of 3.7 tons from a Septemberplanting over a March planting. Both the October and November plantingsalso yielded better than the March planting, but neither was as good asthe September 14 planting. The early planting yield advantage carried overinto the second season as well.

A second study planted the following year gave even more dramatic resultsthan the previous study. First season yields from a September 22 plantingwere 8.9 tons compared to March 14 yields of 4.1 tons, a yield advantageof 4.9 tons the first season. A February planting date was attempted butwas killed by excessive rain.

Both years of these Yolo County studies showed that a September plantingcan result in yields comparable to a second year stand in the first season.

A similar study was planted in 1979 at the West Side Field Station westof Fresno. Here, there was a three ton yield advantage of a September 18planting date over an April 11 or December 13 planting in the first year.This carried over into the second year, with a total yield advantage ofat least 4.5 tons for the first two years for the September planting overeither the December or April date.

Establishing a stand in early fall requires an irrigation system thatcan apply water without standing or crusting. Flood irrigating up alfalfain the early fall is a common practice on sandy loam to loamy sand soilsof the east side of Stanislaus and Merced Counties. A laser-leveled fieldis important in order to avoid high spots. The ground is commonly deepripped, disked, and, if fluffy, rolled before planting. Seed is broadcastand ring rolled or lightly harrowed before flood irrigation. Germinationtakes only a few days for mid-September plantings. Growers will often tryto get one or two additional irrigations on before the rains take over.

On the heavy clay soils of western Merced County, alfalfa growers oftenuse sprinklers to establish a stand in the early fall. They will deep rip,disk and leave the soil quite cloddy before broadcasting seed. The seedis often left uncovered, allowing the clods to melt over the seed. Sometimesa ring roller is used after broadcasting. The sprinklers are run long enoughto completely fill the soil profile, and run times will vary dependingon the moisture content of the soil following the previous crop. One moreirrigation may be necessary before the rains take over. A sprinkler systemwhich can deliver a fine mist can help avoid crusting problems.

Another option for heavy ground is to plant alfalfa on beds, usually60 inches, which can be irrigated up. Bedded alfalfa, although it's moreexpensive to plant, often out-produces flat-planted hay on heavy, poorlydrained soils. It is necessary for the beds to wet clear to the middleor there won't be germination in the center of the beds.

Weed control on early fall plantings is simple if going into a relativelyweed free situation. Often, summer weeds such as pigweed or johnsongrassare the primary problem and these will be killed by winter frosts. Somegrowers will meter EPTC (Genep, Eptam) into the irrigation water if theyare anticipating heavy weed pressure. A stand established early enoughin the fall will usually have sufficient root system to be able to toleratemany winter weed control materials normally used on established stands.It is also easier to time application of seedling alfalfa materials suchas bromoxynil (Buctril)* because the plants have made enough growth toallow their use.

Another advantage of early fall planting is that these fields rarelyhave disease problems and are not subject to drying out when spring rainsdon't come on time. That, coupled with the four plus ton increase in yieldmakes it easy to justify the cost of renting sprinklers, if necessary,to get alfalfa planted during late September.

November 5, 1999