Feeding Your Garden Cane Molasses

Many gardeners are discovering the benefits of adding a little cane molasses to their fertilizer regimen. Some people think that the cane molasses is food for the plant, but that isn’t really true! Plants cannot take up large organic molecules. Complex organic molecules must first be digested by microorganisms in the soil before they can be taken up by the plant. That’s why certified organic fertilizers are not usually recommended as the sole source of nutrients for hydroponics. More often than not it would just make a muddy mess! But in soil, there are plenty of spaces for microorganisms to colonize and make their homes, and plant roots are teaming with microbes. So think of it this way; organic fertilizers feed the microorganisms in the soil, and microorganisms feed the plant.

It’s the same way with the complex carbohydrates in molasses. Plants can’t take up large sugar molecules directly. If and when they do take up complex sugars, plants actually have to expend energy in the process! Instead, plants make most of their own sugars in a process called photosynthesis. When bathed in the energy of full-spectrum light, plants are able to knit molecules of water and carbon dioxide together to make sugars. Some of the sugars are used as carbon skeletons for building plant tissues, and some of the carbohydrates are “burned” to produce quick, available energy for growth, reproduction and cellular repair. Excess carbohydrates are stored for later use, or leaked from the roots to feed beneficial bacteria and fungi in the root zone. In some cases, as much as 30-50% of the energy of photosynthesis is leaked by the plants to feed the soil-born microbes!

As more is discovered about the benefits of plant-growth-promoting rhizobacteria (PGPR), there is a new interest in making compost teas and other microbial inoculants. Water soluble carbohydrates such as micronized cane molasses are an excellent carbon source when making compost teas. As beneficial microorganisms feed on the sugars, they multiply and divide, and in the process they exude many enzymes and co-enzymes. Microorganisms may be thought of as living biostimulant factories, producing growth hormones, amino acids, B-vitamins, organic acids and other powerful growth factors that benefit plants.

Using dried, micronized molasses is a great alternative to using liquid molasses. Soluble-grade, micronized molasses is a powdered product which maintains the quality and consistency of liquid molasses, but adds the handling and storage characteristics of a dry product. During the manufacturing process, ten pounds of cane molasses is reduced to one pound of soluble concentrate, making it much easier to handle and store. If you don’t want the sticky mess of pouring and measuring thick liquid molasses, then powdered molasses is for you. It’s so concentrated that it only takes about 1/8th to ¼ teaspoon per gallon to sweeten your irrigation water or compost teas.

Molasses not only provides a good carbon source for rapid microbial growth, it’s also a good source of iron for plants. Iron is easily locked up in the soil, and it is often the limiting factor for plant growth. But some plant-growth-promoting bacteria make special organic molecules called siderophores. The word “siderophore” literally means “iron carrier”. It is one of the best chelators of iron found in nature. So as the soil bacteria eat the molasses, the iron in the molasses remains soluble and available to the plants. The results? Better color, increased photosynthesis, greater stress tolerance, and sweeter fruit! In fact, many scientists attribute most of the benefits of molasses supplements directly to the greater availability of iron to the plant.

Another indirect benefit of molasses is speeding up the availability of organic nutrients. Although micronized molasses has practically no nitrogen, phosphorus or potassium, the microorganisms it feeds can dramatically improve nutrient availability. Some microorganisms fix nitrogen directly from the air and process it into plant-available form. Other bacteria and fungi solubilize the phosphorus that is locked up in the soil and feed it to the plant. Some microbial byproducts improve the uptake of calcium, and other microorganisms mobilize potassium. Best of all, during their carbohydrate metabolism microbial cells make organic acids that chelate many essential trace elements such as iron, copper, manganese and zinc, making them readily available for plant uptake. Trace elements activate many powerful enzymes, energizing the chemistry of life.

Although cane molasses can be very beneficial for organic production in soil, its best to stay away from sweet products in hydroponics. Most hydroponic nutrient formulas provide about 90% of the nitrogen to the plant in its nitrate form. So if a carbon source is added to the reservoir, a competitive advantage is given to microorganisms that feed on nitrates and make the nitrogen unavailable to the plant. In my own experiments using carbohydrate products in hydroponics, I’ve seen nitrate levels reduced to zero in a matter of days! So don’t add sugars to a hydroponic nutrient formula, especially during the vegetative stage when nitrogen needs are the highest.
In organic soil gardens, however, micronized molasses definitely has its place. Composts supply both carbon and nitrogen, but sometimes they are released too slowly, or they don’t remain in optimum balance with the needs of the plants. Spoon-feeding your plants with water-soluble molasses can help adjust the carbon to nitrogen ratio in the soil and give your plants a boost when they need it the most.

For example, during their establishment, plants are sometimes limited in their carbohydrate production and may not be able to exude enough carbohydrates to support a strong microbial base. So spoon-feeding a little molasses or drenching the roots with compost tea can help boost the microbial populations in the soil that stimulate root growth. Microbial populations can also suffer after times of stress. For example, over fertilizing or poor water management not only affects plants, it can seriously harm beneficial microorganisms in the soil. A spoonful of molasses can go a long way to help the colonies of beneficial microorganisms reestablish themselves, and may even help the plants recover more quickly. Remember, though, that moderation is the key. Too much molasses can cause a bloom of microorganisms that can actually compete with the nutritional needs of the plant!

During the later stages of fruiting and flowering, molasses supplements may show their greatest benefits. Plants tend to get stingy with their carbohydrates during heavy fruit and flower production, preferring to store them in their fruits and seeds instead of leaking them from their roots. So in nature, microorganisms in the root zone begin to go dormant towards the end of the growing season. A boost of carbohydrates can revive the dwindling microbial populations. Carbohydrate supplements are also beneficial when flushing excess mineral salts from the root zone. Simply add a little cane molasses to water and use it in your soil drench, preferably with a little yucca extract. A boost of cane molasses will energize the life in the soil, and help your plants stay productive until the day of harvest!

By Harley Smith