After extensive research and six years of using the oak mulch and leaves on top of the soil here is what the universities, extension services and forest guru's say. On top not mixed in. Living in Florida my garden has never rested for six years. Here is what I found...
(Food for thought & your garden)
Written and compiled by: James Vargas Using locally produced wood chips and leaves are a sustainable activity, keeping a useful product out of the landfill, which is both environmentally and economically beneficial. There are a lot of misconceptions and myths that create controversy. This information is intended to be just FOOD FOR THOUGHT.
- Insures a bumper crop - high yield production
a) Mother Earth’s website states vegetable yields are 50% more productive
b) Creates more uniform moisture for the plant roots. This uniformity and other organic processes as a result of mulching, creates a less stressful environment for the plant, allowing it to be more productive.
- Reduces soil erosion and crusting
a) The organic matter helps to keep the soil crumbly and easy to work. (OSU Ext Svcs)
b) Water droplets from rain or irrigation on a mulched surface can’t directly hit the soil. The soil particles are able to group together or aggregate more. This process increases soil’s air spaces and moisture holding capacity which are necessary to sustain microbial life of fungi and bacteria. This aids in the decomposition process of organic material.
c) Worms further work their magic reducing material and aggregate it even further.
- Moderates soil temperature
a. The Cornell University study reports that mulched plot’s summer soil temperatures were reduced by 8 to 13 degrees. This prevents the sun from wreaking havoc on tender vegetation by lowering soil temps.
b) Protects the plant root system in the winter.
- Conserves water = Less watering
a) The same study found the soil moisture content in mulched plots were two times as high. b) The Oregon State University Extension Svc Master Gardener program states moisture moves by capillary action to the surface and evaporates, if mulch does not cover the soil.
- Improves Soil nutrients
a) Mulch breaks down into organic soil, rich with a variety of microbes. A variety of
mulched material increases the variety of microbes increasing the variety of plants
b) Organic mulches condition the soil and furnish food for earthworms, which are
valuable in aerating the soil.
c) Organic Gardening cited a Washington State University study that found sand turned
into rich black soil full of life.
d) Our own experiments here at Temple Terrace Community Garden has proven this to
be true. Our pathways were mulched early on. Originally very sandy. I found the paths
to have better soil than the plot itself. I started using that soil once it broke down and
then re-mulch the path. Later- after attending a class put on by a local garden - Willow
Garden - I started mulching the garden.
- Less weed growth = less weeding
a) More time can be and is spent on trying to control weeds than any other home
b) Mulching with oak and other like mulches decreases the likelihood of weed seeds
germinating. Be careful – as I will mention later - some straws and hay must be aged
to rid it of the various seeds that if left in the hay or straw will lead to a marked
increase in weeds.
c) Cornell University study reports that the time required to remove weeds in a
mulched areas was reduced by two-thirds. In my opinion and experience here, a
lot less time is involved than mentioned in the study.
d) Seeds of most grasses, weeds and plants will not germinate where oak mulch meets
the soil and about one inch into the soil. A few types will germinate.
- The truth of the matter (organic mulch matter)
a) Oak leaves and mulch will lower the PH and make the soil too acidic.
i) According to Oregon State Extension Services and Horticulture magazine and
other sources – In all but the sandiest soil the PH is strongly buffered meaning
it does not fluctuate.
ii) This study as well as other sources state - PH changes very little after applying
iii) Research over the years has not demonstrated any detrimental effect of wood
chips on established plants.
iv) Although oak leaves have an acid PH (4.5 to 4.7) when they are fresh, the
breakdown products are neutral to slightly alkaline. This holds true for several
mulches like pine bark, pine needles and related materials that are considered
acidic. According to the Forest Industry Council of Australia, pines do not harm
the soil and various studies have found no evidence of soil acidification in the pine
v) I have used only oak mulch in my plot for five years or more, layer upon layer, with no seasonal breaks and recently tested my soil PH at four to six inches of depth. I found my PH to be right at 7.0 – neutral. b) Woody oak mulches, leaves, pine needles, pine bark remove nitrogen from the soil i) This only occurs where the oak and woody materials meet the soil surface. The effect is minimal. Most seedlings do great just one or two inches below the surface. (i) Put a fine layer of decomposed mulch on top of the soil, then add a layer of fresh non decomposed mulch on top. This will help alleviate that neutral zone of low nitrogen that may affect seeds. The top fresh layer will combat germination of the undesirable grasses and weeds. The top layer should be 2-3 inches thick and minimal contact with new seedlings. (ii) In addition - If you are still concerned, add a layer of high nitrogen fertilizer to the surface soil before mulching such as blood meal if you are planting seeds or small seedlings. (iii) Planting small plants that are already established – like the ones you purchase from a nursery will be planted well below the surface away from this area. (iv) Research over the years has not demonstrated any detrimental effect of wood chips on established plants. (b) In a vegetable garden do not till if you are using these woody mulches and do not use the wood chips below the surface. It will tie up some nitrogen where the plant needs it most, at the roots. Vertical tilling also disrupts the microbial community established in the soil.
ii) Over time, nitrogen increases when using woody or oak chips as mulch - states a 1971 Cornell University 15 year research study.
- What are my options other than oak chips?
a) Oak leaves
i) Breaks down to one of the best organic materials to feed your plants.
ii) When using oak leaves as mulch it is very important that:
(1) The first layer to touch the soil needs to be small particles of FINELY decomposed leaves.
(2) The layer above the decomposed layer can be whole leaves – preferred chopped. Not too thick or water will not reach the soil.
i) Breaks down into excellent nutrients.
ii) Great for starting seeds (mulch 5-6 inches thick for seeds).
iii) Retains moisture : good for seeds that you have planted – not good in constant rainy conditions – mold, mildew
iv) Choose a high quality hay – less seeds. Some hays may be a weed/seed haven and need to be aged past the seed stage or slightly composted.
v) Check your local feed stores for old bales at a substantially lower price.
We have a gardener here that used hay to mulch in her garden at the beginning of the season and reports no weed problem at all.
c) Straw i) cover only, no nutritional value
- Mulches not generally used in vegetable garden
- Mulches such as chipped hard and softwoods, cedar, cypress and
pine bark aren't used much in vegetable gardens. They will last the
longest because they are resistant to decay. Use those mulches around
- Painted /dyed mulches
- Rubber mulches
i) If you mix sawdust into your soil, nothing will grow there for a year or more. Pure wood materials like sawdust and wood shavings are super-high in carbon, and their carbon will absorb all of the plant-feeding nitrogen in your soil in its quest to decompose. Mix with other organic material.
ii) Prone to compaction
iii) Where did the saw dust come from. What wood materials? Pressure treated, hard woods, cedar?