at Snakeroot Organic Farm
Mulching With Organic Materials
presented at Rural Living Day
9:45-11am, Saturday March 31, 2012, Mount View High School
Mulching imitates nature.
Most forest and grassland soils were created through millenia of dead leaf materials falling to the ground as a mulch year after year and slowly rotting into soil-forming humus. At Snakeroot we annually apply organic mulches to about two acres of crops. Where annuals are grown the mulches are annually incorporated into the soil. In perennial plots, new layers are just added year after year.
As with any program of weed control, it is important to know the strengths and weaknesses of the weeds you are combating and adjust your mulching practices and materials accordingly.
But first, let’s get our terms straight: Mulch is any material applied to the surface of the soil primarily for weed suppression and moisture retention. Mulching means applying mulch. Shredding is breaking course materials into finer ones. Compost is a soil additive created by a controlled rotting process usually done in a pile a small distance from where the crops are grown. Sometimes compost is used as a mulch on the soil surface, but this is not its best use. Often materials such as brush and twigs need to be shredded before they can be effectively used as a mulch or added to a compost pile for rotting.
Mulches come in many types.
Many farmers and gardeners use mulches, and most of them use plastic mulches because they are easily applied, relatively inexpensive to purchase, and are quite effective at some mulching functions. However, plastics are basically oil, and their one-season use followed by removal and disposal in that mythical place called “away” seems to me to be the antithesis of a good organic farming practice. There have also been trials of starch-based biodegradable plastic mulches, paper mulches, spray-on reflective mulches, and spray-on slurry mulches.
At Snakeroot, we use only organic mulches, and no plastic mulches. Not “organically grown” but rather organic, once alive material. Our toolkit of mulches consists of whole leaves, shredded leaves, pine needles, old hay, fresh cut hay, wood chips, sawdust, cardboard and newspaper. Over the years we have found each is most effective at a particular job, for a particular crop, or to combat a particular weed. And we have adjusted our needs to be compatible with the amounts of each that is available to us, and have learned where we can make acceptable substitutions of one material for another.
Reasons to mulch.
Mulching, like most processes in biology, has multiple effects. We use organic mulches to:
- Suppress weeds by shading the soil surface and smothering any already sprouted small weeds. The soil surface is now dark and moist but sprouting weeds run out of energy before they can emerge thru the mulch. Some weed seeds cannot live more than a year or two without dieing, so those we kill by keeping the soil mulched for two successive seasons in some of our rotations.
- Retain soil moisture by providing a barrier to soil moisture evaporation, while allowing rain to penetrate (unlike plastic mulches). We only have two five-gallon-a-minute wells with which to do all of our vegetable washing for market and irrigation of the fields. This means that by mid August we usually are close to running a water deficit in the soil. We have found mulching reduces the stress from lack of rainfall or irrigation because the soil stays quite moist under the mulch. Years of incorporating mulches into the soil at season’s end has given us a high soil organic matter content, which also helps the soil itself to act like a sponge.
- Deepen the soil, since without a mulch the top half inch of soil gets too dry to allow root growth during the growing season. Without a mulch, you are effectively mulching your soil with your top layer of soil.
- Add organic matter at the end of the season. Annually disking in several inches of mulch adds huge quantities of organic matter to the soil, adding minerals from the mulch into the soil and invigorating microbial life. This decomposition process actually begins before the mulch is turned under, as you can see by trying to determine the exact dividing line between soil and mulch at the end of the season. Earthworms and microbes have turned this once clear demarcation into a continuum.
Crops we don’t mulch: Short season crops like basil, radishes, carrots, dill, broccoli. It just isn’t worth the labor. Spreading crops like lettuce, cabbage, or napa, that would stay too wet and provide food for slugs protected by the mulch.
ANNUALS: total 74,000 sq. ft.
Tomatoes: 20,000 sq. ft. Whole leaves cover the entire tomato plot. Leaves are applied in late June before broadleaved weeds get too big and after the June sun has warmed the soil in the beds where the tomatoes are planted. Leaves are tucked around each tomato plant (about 3,000) just before the plant is ready to fall over. The mulch suppresses weeds, retains soil moisture, keeps the rain from splashing soil onto the plants or fruit. The leaves do support small populations of mice and slugs, which sometimes generate a slight damage. After frost, vines and leaves are turned under with a disk harrow. There is such a mass of organic matter that it requires several passes over a two week period. Then we plant . . .
Garlic: 17,000 sq. ft. Shredded leaves or pine needles are spread 3-4 inches deep on top of the beds after garlic is planted in October. These will not mat down during the winter as whole leaves would, thus suppressing garlic emergence. Whole leaves are used in aisles between beds to suppress weed growth; the fact that these do mat down over the winter helps suppress weeds. Both retain soil moisture and are left on the entire season. After garlic harvest in early August, fall crops of broccoli, cabbage, and lettuce are transplanted directly thru the remaining mulch. Since broccoli harvest lasts late into the fall, the whole patch is disked under in the spring. At that time the mulch is 18 months old and decomposes quickly.
Onions: 17,000 sq. ft. Onions are started in mid February, then transplanted to the field in mid to late April. Plants are allowed to grow several weeks until they are 6-8 inches high. The beds are then mulched by hand with shredded leaves or leaf mold (when we have it). Shredded leaves fit in between the delicate onion plants more easily than any of the other materials we could use, and they pack down well eliminating light from the soil surface. Once the beds are mulched, we mulch the aisles with whole leaves (if we have enough) or newly cut hay. Newly cut hay comes from about three acres of fields around our gardens that we mow with a string trimmer, getting several cuttings a year of young seedless hay 6-12 inches long. Newly cut hay will shrink down to about half thickness within two weeks, so it is put on rather thick to start with.
Kale, leeks, celery, celeriac, Brussels sprouts, Swiss chard: 10,000 sq.ft. We group these crops together because they are in the same spot all season long, are upright in nature, and benefit from mulching. We usually have to hoe and hand weed at least once until we have enough mulch generated to use on them. For all these we use newly cut hay. Celery and celeriac always get first crack at the mulch since they require a good moist soil.
Winter squash: 20,000 sq. ft. Winter squashes get planted in early June and each variety is mulched before it begins to run with old hay and with hay cut by our flail mower. This delay between planting and mulching allows time for the soil in the beds to warm before applying the mulch. Plants in the beds are mulched first, then we go back and mulch the aisles with more of the hay.
PERENNIALS: total 4,600 sq ft.
Rhubarb: 2,500 sq. ft. Rhubarb loves moisture, so as soon as rhubarb has emerged in the spring (wait until emergence so you can tell where the plants are but before the perennial weeds have grown) we mulch them with 1/4” of newspaper overlapped by at least 6 inches. Wetting the newspaper first allows it to conform better to ground irregularities, to bond at the overlaps, and to keep from blowing away if the day is breezy. We tuck the newspaper right up to the plants. Over the newspaper we apply leaves, hay or wood chips to hold the paper in place. The weeds we are combating are morning glory and witch grass. Some years we also apply a thin layer of compost before the newspaper. In sections where the weeds are especially vigorous, we may need to do this annually for two or three years until the perennial weeds are knocked back enough not to be a problem. After only one year, the newspaper is impossible to find and thus no longer provides a barrier to weed emergence. Although rhubarb is a tremendous competitor in May and June, after July it offers little competition to any weeds for the rest of the season.
Grapes: 700 sq. ft. and Blackberries: 500 sq. ft. With both Grapes and Blackberries we add a thin layer of compost, then newspapers or cardboard, then hay or wood chips or pine needles on top. This provides fertility for the season or two as well as weed suppression and water retention. Part of the fertility is from the continually rotting mulch that represents a slow release fertilizer. We usually have to repeat this procedure about every two years, or annually in those spots where the witch grass is extra vigorous.
Perennials Herbs: 900 sq. ft. We grow sage, thyme, oregano, winter savory and tarragon together in their own garden, which we annually mulch with new-cut hay. We mulch both the aisles and between the plants in the row as we work our way down the aisles. Only a few dandelions seem to survive this technique, at least for the first five years.
GREENHOUSES: total 6100 sq. ft.
In our five greenhouses, we grow crops in the ground, and that ground is mulched with new cut hay, and sometimes shredded leaves. Our greenhouse cropping system has cukes, cherry tomatoes and peppers growing during the summer months. In the fall, the vines are added to the compost pile and the mulch is removed and used at the edges outside the greenhouses for grass suppression. Compost is then added to the beds and they are planted to spinach, lettuce, spicy greens and beet greens for spring harvest. During their harvest, we transplant peppers, cukes and cherry tomatoes right into the beds of growing greens. Once the greens harvest is completed, the beds are mulched, often without removing the leftover greens crop, or pulling it to add to the mulch.
Where do we get our mulching materials?
Old Hay: People who bank their houses for the winter, local farmers who want to clear old hay bales from a field or who have quantities of spoiled hay. New Cut Hay: Small, irregular patches we mow with a Stihl string trimmer, hand rake into piles for pickup with a hay fork. Large smooth fields we mow with a flail mower, rake with a side delivery rake, hand pitch into a wagon and haul to the crops. Leaves and Pine Needles: We have an arrangement with the Town of Pittsfield that sends all residents with leaves and pine needles to us instead of to the transfer station. We are open any daylight hour, seven days a week, so the residents actually find it easier than going to the dump, and many appreciate that we are recycling the product of their hard work. The Town estimates we annually recycle around 55 tons of materials and save the town’s taxpayers thousands of dollars each year in Transfer Station costs. Shredded Leaves: Some people in town gather their leaves with their bagging lawn mower, and some lawn care companies will vacuum up leaves into an enclosed trailer. Both methods nicely shred the leaves. The commercial outfits are delighted they don’t have to pay tipping fees at the transfer station. Wood Chips: Sometimes residents grind a stump that was in their way. Some years a tree trimming company is trimming brush from under and around the power lines, and when their truck is full, they need to dump it. Whenever we see them in town, we stop to remind them that we will take as many loads as they will deliver to us. We also have a Finnish PATU Model 40 pto driven brush chipper we occasionally use on our own brush. We especially like making alder chips, since they easy to chip and rot down so nicely, plus the alders re-grow for chipping again every eight or ten years. We do not use chipped demolition debris!
Mulch Application Notes
Cost: We save considerable money in not having to annually buy plastic mulches, and we save labor by not having to annually apply, remove and dispose of plastic mulches. However we do have to provide space to store our bulky organic mulches and then to transport them to the field, which generally means dozens of trips with tractor and wagon. We then have to apply our mulches by hand, and as a result we have a crew of three or four “mulch application specialists” engaged in moving, harvesting hay, and applying mulches for at least two months straight from mid-May to mid July and again in October, so the labor costs are far higher than with plastic mulches. However, the money is now going to local farm-working folks rather than to global petrochemical companies. And that seems more like old style organic to me.
Placement: In existing plantings, the mulch goes right up to the plant, being sure to leave no “light holes” where a weed seedlings would find encouragement. In beds of a crop that is to emerge thru the mulch, the mulch should completely and evenly cover the bed, and should be of a nature that the emerging crop can pierce easily, such as shredded leaves or pine needles.
Pine Needles: Many folks are afraid to use pine needles as a mulch or in compost because of the fear that they will create acidic conditions. Occasionally a town resident will even apologetically ask us if we take them. A few years back, the University of Connecticut at Storrs conducted a five-year mulching experiment to see if pine needles did indeed acidify the soil. They found that they did not, and that their affect as a mulch was greatly beneficial. They do need to be placed thicker than, say, shredded leaves, since they pack so loosely and allow light through more easily. When incorporated into the soil, they add organic matter, and adding organic matter results in the production of huge and complex humic acid molecules which tend to buffer any pH change that might have occurred.
Applying the mulch: Mulch is usually stored at each end of a field and perhaps along the edge, then it is brought in for placement in bulb crates and/or a wheel barrow. The single wheel of a wheelbarrow negotiates the narrow aisles better than any two wheeled cart ever could. Since the beds are usually too wide to mulch all from one side, two “mulch placement specialists” move along each side of a bed, meanwhile keeping each other company. In areas where plants won’t be damaged by rapid mulch placement, mulch can be dumped into piles then spread around, or poured and shaken from a crate to just the right depth.
Miscellaneous Tips:
- Dry leaves need to be applied thicker than wet leaves. They are also more prone to blowing away in high winds.
- Shredded leaves are denser than whole leaves and do not create an impenetrable mat like whole leaves do.
- People are amazed when you thank them for bringing you a “waste” product that to you is valuable but to them is worthless.
- Care must be taken if the plants need to be moved to assure complete ground coverage. Peppers are especially brittle.
- Incorporation of mulches into the soil is usually done in the fall to allow time for the residue to rot enough so as not interfere with spring seeding.
- Organic mulches keep the ground cooler—an advantage in the hot summer—but may result in slightly later emergence of perennials and garlic in the spring.
