Ted Cook's 35-acre alfalfa field produced more hay in its final year than in any of the other eight. Although he didn't follow all the recommended procedures, he added two years to the life of the thinning stand by adding grasses.

In spring 2007, this Modesto, CA, grower interseeded 25 lbs/acre of a commercial mixture of annual and intermediate ryegrass, tall fescue and festulolium. Then his fertilizer supplier, Salida Ag, applied 293 lbs/acre of a liquid mixture containing nitrogen, phosphorus, potassium, calcium, sulfur and zinc.

“We broadcast the seed, and everyone told us that it wouldn't grow in alfalfa, but it grew beautifully,” says Cook.

He took six or seven cuttings per year from the flood-irrigated field and packaged the hay in 125- to 150-lb bales. He feeds it to his 400-head registered Angus herd, and isn't concerned about quality.

“It's not dairy grade, but the cattle seem to love it,” he says of the alfalfa-grass mix.

He figures the stand would have remained productive two additional years, but recently plowed it down so he could relevel the field. He planted oats, which will be followed by sudangrass. Then he'll go back to alfalfa in two years. When that stand starts to thin, Cook won't hesitate to interseed grasses again.

“I think the seed mixture and the fertilizer use will vary throughout the country, but it sure works here,” says Cook.

Interseeding can work, but “it's not necessarily something that I'd recommend all the time,” says Paul McCormick of Stanislaus Farm Supply, Cook's seed supplier. “It really depends on the person's situation.”

He sees it as an alternative “if folks have an old alfalfa stand that they want to stretch another year, the horse hay market will accept that kind of a product and they want to take the risk.”

But he usually recommends planting a single grass species, such as tetraploid perennial ryegrass or festulolium, rather than a mixture. In northern California, interseeding should be done in fall to increase the odds of success, he adds.

“That way you have a winter for it to get established, and in our climate that's necessary to have good production the next summer,” says McCormick.

Use a drill, if possible, or if you broadcast the seed, harrow the field afterward to cover it.

“Any step, in my opinion, short of a drill is a risk,” he says.

Fertilization should be done according to soil test. Some nitrogen probably will be needed to supplement that provided by the alfalfa. The amount to apply will depend on how badly the alfalfa stand has deteriorated.

“If you've got a lot of open space, you're going to have to push it hard with nitrogen to make that grass keep up with the alfalfa,” says McCormick.