Given enough moisture and the right acidity (or alkalinity), alfalfa (Medicago sativa) can grow anywhere. 

Except for places where it needs to be irrigated to be kept alive! 

M. sativa needs a minimum of 8 to 10 inches of rain every growing season and soil pH between 6.4 and 8.0 (?) in order to grow, flower, and set seed. It’s a cool-season legume, meaning that it will start growing when temperatures get above 5 degrees Celsius, and shut down when it gets above 25 degrees. 

With it being a nitrogen-fixing plant (as are all legumes and future legumes I will discuss in the coming months), it has a mutually beneficial relationship with rhizobacteria. Rhizobacteria are the ones that help M. sativa to “fix” nitrogen. They infect the roots of their host plant, encouraging the root cortex to grow around the bacterial colonies creating nodules which protect the bacteria within. There, the bacteria help the plant capture free nitrogen from the atmosphere. 

Healthy nodules are pink to blood-red in colour. The deeper the colour, the more actively the plant is fixing nitrogen. Most nitrogen fixation happens when the plant is vegetative or focused on growing leaves and roots below ground. Nitrogen fixation diminishes when the plant puts its energy into flowering and producing seed, causing the nodules to turn white. 

However, alfalfa undergoes “indeterminate growth,” meaning it will continue growing leaves and stems while flowering and producing seeds. Only when growing conditions get too cold, or a killing frost destroys the plant cells will it terminate growth until next spring. As such, nitrogen fixation may continue with this type of growth but is still less than its vegetative stage.

M. sativa primarily has a tap root that can reach 10 to 20 feet into the soil. Some “creeping” varieties are bred to produce rhizomes which produce daughter plants. Other roots grow laterally for the purpose of energy storage, capturing moisture, and feeding soil organisms. Alfalfa is a heavy water user, making it useful if there is a high water table that you might be having issues with; however problematic if annual rainfall is under 10 inches per year. 

With M. sativa being the “queen of forages,” it is selected heavily for yield, high-quality nutrient value, quick regrowth, and competitiveness with other plants. Unfortunately, selection processes for such traits have made new varieties shorter-lived than older varieties, especially if not given the chance to reseed themselves and adapt to the environment it’s grown in. For most of the newer varieties, the stand peaks at 4 to 5 years and declines afterward, forcing producers to either expense out fertilizers to keep the stand going or invest in reseeding the forage stand entirely. 

Re-establishment is difficult because plant residue from old alfalfa plants prevents new seedlings from establishing, let alone germinating altogether. This is primarily leaf litter, not roots, as is commonly believed. This leaf matter feeds a certain type of bacteria that attacks the new seedlings trying to germinate, destroying their chance of establishing. When alfalfa seeds are trying to germinate beyond the drip line of old alfalfa plants, they are safe. It’s when they’re within or beneath that canopy that they’re in trouble. 

Cue the frustration in producers’ voices when I tell them about that. The only option to put new alfalfa back in the stand is to put it out of production for a full growing season to allow the dead leaves to decompose fully. Seeding in a forage stand (annual or perennial) that contains anything but alfalfa (this allelopathic toxicity only affects Medicago spp. and does not affect clovers or vetches) is the best advice I can give until the following year when it’s safe to re-seed to alfalfa or an alfalfa-grass mixture. 

Otherwise, you end up with a patchy alfalfa stand or a complete trainwreck where almost nothing grows. 

Did you know that one pound of alfalfa seed contains over 650,000 seeds? They should also be coated with an inoculant so that the seedlings have a good chance of survival. 

Once established, alfalfa is made great for hay, silage, or grazing. It’s more “hot” when fed by itself as a monoculture stand than if it’s grown with one or more forage grass species such as smooth brome (Bromus inermis), timothy (Phleum pratense), or tall fescue (Lolium arundinaceum), for example. Alfalfa alone has an average crude protein content of 25% and ADF of 30%, which means it’s easily digestible and quick to add muscle in beef steers or milk fat in dairy cows. 

A bit too good at being digestible, that is. Alfalfa has also gained severe notoriety and infamy for causing frothy bloat in ruminants. The proteins are released quickly, and the plant cell walls are so easily broken down by rumen microbes that tiny, slimy bubbles form in the rumen. The ruminant relies on eructating (burping) the gasses from the act of fermentation every minute in order to continue eating and living, but when this is stopped by fast protein digestion, trouble begins that is often life-threatening if not caught immediately. 

The more the bubbles accumulate, the more gas is held back, further distending the rumen to the point where the animal finds it difficult to breathe. A significant amount of pressure is put on the lungs, slowly asphyxiating the animal to the point of no return (death). 

If caught in time, removing them off the feed and tubing the animal with mineral oil or dish soap helps break those tiny gas-filled bubbles and release all that pent-up gas. Or, in emergency situations, a trocar to the left side where the rumen wall meets the abdominal wall may be needed, requiring sutures once the danger has passed. 

The good news is that some forage breeding and research have been done to make a “bloat-free” variety, at least here in Canada. AAC Grazeland is a variety reported to have 80% bloat reduction potential. It’s not bloat-free but has been bred so that proteins aren’t as quickly digested as in other varieties. Good news for graziers.

Alfalfa shouldn’t be grazed by itself, though. A good grazing mixture should be 30 to 40% legume, including alfalfa and other species from grasses to broadleafs. This way, animals have a higher selection plane for nutrition and other phyto-compounds (like tannins) for gut health, productivity, and overall health. 

I have one more interesting tidbit to share before I let you all go for this month: Medicago sativa shares a close cousin, Medicago sativa spp. falcata. M. s. falcata is called “Yellow-flowered alfalfa” or “Siberian alfalfa.” It has much smaller trifoliate leaves than M. sativa, and all flowers are a bright yellow. Not as common as its Common Alfalfa brethren, but it’s tougher in that it can grow in some areas where M. sativa won’t. It’s become naturalized in northern Alberta, British Columbia and Saskatchewan and remains a productive (bloat-reduced) forage plant for hay and grazing.