CMG GardenNotes #245 Mulching with Wood/Bark Chips, Grass Clippings, and Rock

Transcription

1 CMG GardenNtes #245 Mulching with Wd/Bark Chips, Grass Clippings, and Rck Outline: Terms: mulch and sil amendments, page 1 Benefits f mulching, page 1 Edging and sil grade, page 2 Wd/bark chip mulch, page 2 Benefits, page 2 Prduct selectin, page 3 Cedar mulch, page 3 General use, page 4 Depth, page 4 Arund trees, page 4 Windy areas, page 4 Chips ver landscape fabric r newspapers, page 5 Cnverting lawn t a mulch area, page 5 Cultivating chips int the sil, page 5 Grass clipping mulch, page 5 Newspaper under mulch, page 6 Rck mulch, page 7 Summary: cnsideratins in selecting mulch, page 8 Terms: Mulch and Sil Amendments The term mulch refers t a material placed n the sil surface. By cntrast, a sil amendment refers t any material mixed int a sil. Benefits f Mulching Depending n materials used, mulches have many benefits, including the fllwing: Reduces evapratin frm sil surface, cutting water use by 25-50% Organic mulches prmte sil micrrganism activity, which in turn, imprves sil tilth and helps lessen sil cmpactin. Fr additinal details, refer the CMG GardenNtes #211, The Living Sil. Stabilizes sil misture Prevents sil cmpactin Cntrls weeds, which rb sil misture Mderates sil temperature extremes 245-1

2 Cntrls ersin Gives a finished lk, imprving aesthetic quality Edging and Sil Grade It is a cmmn practice t add mulch abve grade level. Withut a defined edge, the mulch can spread ff the bed nt lawns r sidewalks, creating a mwing r trip hazard. [Figure 1] Figure 1. Mulch added abve grade spills ut nt the lawn r sidewalk. An effective alternative is t drp the sil level n the mulch bed 3 inches s the tp f the mulch is at grade level. Hwever, ensure that the mulched bed des nt fill with water draining frm higher areas. [Figure 2] Figure 2. T keep mulch in place, drp the sil level in the mulch bed s the tp f the mulch is at the grass r sidewalk level. An effective alternative is t rund dwn the sil level alng the edge f the bed. This gives a nice finished edge at grade level and creates a raised bed effect fr the flwerbed. [Figure 3] Figure 3. An alternative is t taper the sil level alng the edge f the bed. Wd/Bark Chip Mulch Benefits Wd r bark chip mulch is great arund trees, shrubs, perennials, and small fruits. [Figure 4] A wd/bark chip mulch creates a favrable envirnment fr earthwrms and sil micrrganisms. Over time, this helps reduce sil cmpactin. Fr additinal details, refer t the CMG GardenNtes #211, The Living Sil, and #218, Earthwrms. In perennial and shrub beds, wd/bark chips can reduce the need fr irrigatin by as much as 50%. Mulching materials that mesh tgether are mre effective at reducing water evapratin frm the sil. When placed n the sil surface as mulch, wd/bark chips d nt tie-up sil nitrgen. Hwever, incrprating wd/bark chips int a sil can create a nitrgen 245-2

3 deficiency due t a carbn-t-nitrgen imbalance, and can interfere with seedbed preparatin. It takes ten r mre years fr chips t decmpse in a typical sil. The use f fine chips r sawdust as mulch can tie-up sil nitrgen and can decrease sil xygen levels. Wd/bark chips are nt recmmended in vegetable r annual flwerbeds where the sil is rutinely cultivated t prepare a seedbed. Figure 4. Wd/bark chip mulch in the perennial and shrub bed greatly enhances sil tilth ver time. Prduct Selectin There is a wide variety f wd and bark chip prducts available fr mulching. Wd chips have the advantage that they decmpse faster, enriching the sil. Bark chips decmpse slwer, requiring less frequent replenishment. Primary selectin is based n desired appearance and cst. Sme can be clred t match the paint clr f the hme r landscape features. Cedar mulch A number f references discuss the phyttxicity f cedar when used as mulch arund yung plants. Mst f the infrmatin, hwever, refers t the use f cedar sawdust (smaller particles with mre expsure t the surrunding plants and their rts) rather than chips that are typically used as mulch. The ther issue, and prbably the mre relevant questin, is what plant is actually referred t as cedar. In Clrad, we have very few true cedars (the genus f true cedar is Cedrus). What mst peple call red cedar is either a juniper (i.e., eastern red cedar, Juniperus virginiana) r arbrvitae, (i.e., western red cedar, Thuja spp.). Neither f these have txic qualities fr yung plants when used as a mulch. Mst cedar mulch in Clrad (unless they are bagged and shipped frm anther part f the cuntry) will nt be the true cedar. They will mst likely be either the juniper r arbrvitae, which are nt txic when used as mulch. If yu are buying mulch in bulk frm a lcal surce it likely des nt cntain wd frm true cedars

4 General Use Depth The desired depth f wd/bark chips depends n chip size. Smaller size chips shuld nt exceed a ne t tw inch depth. Larger chips are typically applied at three t fur inches deep. Thicker layers may reduce sil xygen. Additinal mulch needs t be added every few years t bring the mulch depth back t the desired amunt. With the larger chips frm the tree pruning industry, three t fur inches are needed fr effective weed cntrl and t eliminate the cmpactin frces f ft traffic. It is cmmn t see where the mulch is t thin and des nt prvide fr weed cntrl and cmpactin management. On cmpacted and/r clayey sil, three t fur inches f wd/bark chips may reduce water evapratin frm the sil surface s much that susceptible plants develp rt rts in wet years r under frequent irrigatin. In wet sil situatins, mulching may be undesirable as it may help hld excessive water leading t rt rts. Arund Trees Wd/bark chip mulch is great fr trees and shrubs, prtecting trees frm lawnmwer damage. Hwever, d nt make mulch vlcanes arund tree trunks by applying chips up against a tree s trunk. Wet chips piled up against the trunk can cause bark prblems and interfere with the natural trunk taper, making the tree mre prne t wind thrw. Keep the mulch back at least 6 frm the trunk. [Figure 5] Figure 5. Never make a mulch vlcan. It leads t decay f the bark and interferes with trunk taper. Keep mulch back six inches frm the trunk. Windy Areas Wd/bark chips mve in strng winds. It is reprted that the shredded type chips are smewhat mre wind resistant. Basically, wd chip mulch des nt wrk in pen windy area, like n the high plains. In subdivisins, the wd fence arund yards may adequately blck the wind. Wd/bark chips als flat, and are nt suited t areas with standing water r heavy surface runff during heavy rainfall

5 Chips Over Landscape Fabric r Newspapers It is a cmmn prcedure t apply mulch ver a landscape fabric t reduce weed grwth. Hwever, the chips will give a greater imprvement n sil tilth where they can breakdwn int the sil withut the fabric layer in between. Weed grwth in a mulch bed is a prblem when the mulch is nt at an adequate depth. As an alternative t the weed fabric, maintain a prper mulch depth t manage weeds cming fr seed. Weed seeds that germinate abve the fabric layer will be difficult t pull. Cnverting Lawn t a Mulch Area In situatins where a lawn is being cnverted t mulched beds, spray the lawn ut first with glyphsate (the active ingredient in Rund-up and ther prducts). Apply the mulch after the lawn has died. D nt put mulch ver a grwing lawn. Cultivating Chips int the Sil D nt cultivate wd/bark chips int the sil. The high carbn cntent f the wd prduct ties up sil nitrgen. Chips create sil texture interfaces that interfere with air and water mvement and rt spread. Chips decmpse nly slwly, taking apprximately ten years. Wd/bark chips n the surface d nt tieup sil nitrgen. Hwever, d nt use sawdust fr mulch as it may tie up sil nitrgen. Wd prducts need t be cmpsted befre use as a sil amendment. Grass Clipping Mulch Grass clippings make gd mulch when applied in thin layers and allwed t dry between applicatins. Add additinal layers each week as the lawn is mwed. With a few layers, weed seed germinatin will be checked. Grass clippings decmpse rapidly, requiring additinal layers during the grwing seasn. A grass clipping mulch recycles its nutrients int the garden bed. D nt apply fresh grass in thick layers as it will mat, prduce ful drs, reduce air and water infiltratin, and even becme hydrphbic. D nt use clippings frm lawns that have been treated with herbicides, r ther pesticides, fr at least 4 weeks after applicatin. Grass clippings are a gd chice in vegetable and annual flwer beds that receive annual cultivatin t prepare a seedbed. Arund leafy vegetables (such as lettuce, spinach, chard) carefully place the mulch at the base f the plant, t avid getting dry grass clippings stuck t the lettuce leaf. [Figure 6] 245-5

6 Figure 6. Grass clipping are great fr the vegetable garden and arund annual flwers. Directly frm the bag, place them arund the plants in thin layers, allwing each layer t dry befre adding mre. Newspaper Under Mulch Newspapers make a gd underlayment fr a wd/bark chips r grass mulch. The newspaper shuts ut light, giving a quick stp t germinating weed seeds that were brught t the sil surface during cultivatin fr seedbed preparatin. Newspaper shades ut many, but nt all, grwing weeds. Apply newspapers nly ne t tw sheets thick and tp with wd/bark chips r grass t hld it in place. As newspapers blw away with the slightest breeze, apply it just befre cvering with chips r grass. D nt use thick layers f newspaper; the high carbn cntent can tie-up sil nitrgen. [Figure 7] Figure 7. Use newspaper under the grass r wd/bark chip mulch t shut ut light and stp weed seed germinatin. Apply it nly in thin layers t prevent a carbn t nitrgen imbalance. In situatins where the newspaper is wet frm rains r sprinkler irrigatin, it rapidly decmpses. Where it remains dry (like ver a drip irrigatin system) it may still be intact at the end f the grwing seasn. Any remaining newspaper may be cultivated int the sil in the fall. Newspapers are printed with sy-based inks and are safe fr use. D nt use glssy magazines as their inks may cntain heavy metals r ther sil cntaminants

7 Rck Mulch Rck ver landscape fabric is a cmmn mulching material ften cnsidered as lw maintenance. It is the preferred material fr nn-plant areas. Rck mulch has the advantage ver wd/bark chips that it des nt blw, flat, r require additinal amunts every few years as it decmpses. [Figure 8] Pea gravel ver a weed mat helps reduce evapratin frm the sil surface. The use f small size rck, such as pea gravel, has been reprted t encurage plant grwth due t warmer sil temperatures in the springtime. Hwever, in Clrad s climate this may encurage early grwth that is sensitive t late spring frsts. Figure 8. Rck mulch is great fr nn-crp areas Rck mulch may be desirable in sme specialty gardens, like a cacti garden, rck garden, r alpine garden. Rck mulch can becme a heat sink, creating a significantly warmer afternn, evening, and nighttime micrclimate. Outdr peple space adjacent t rck mulch will be warmer and less cmfrtable fr summertime afternn and evening use. In planting beds, rck mulch increases temperatures and may increase water requirements. Rck mulch may interfere with shrub rejuvenatin. Refer t CMG GardenNtes #619, Pruning Flwering Shrubs, fr details n shrub pruning. Because shrubs in rck mulch cannt be effectively renewed by rejuvenatin pruning, they are replaced when the shrubs becme vergrwn and wdy. In this situatin, it wuld be better t cnsider the rck mulch as deferred maintenance rather than lw maintenance. [Figure 9] Figure 9. Rck mulch interferes with shrub rejuvenatin pruning. Here a wd/bark chip mulch will help enhance sil tilth

8 Avid using rck mulch beds adjacent t lawn areas. Rcks in the lawn are a safety issue with lawn mwers and ruin mwer blades. Fr safety, avid using rck mulch in children s play areas. Rck ver black plastic is very undesirable fr planting areas. The plastic will reduce air infiltratin int the sil and create sil misture prblems. The sil is ften very dry r very wet under plastic. Summary: Cnsideratins in Selecting Mulch Gardeners ften inquire abut the best mulching material fr their situatin. There really is nt a best. What is practical and available varies frm gardener t gardener and within different cmmunities. The fllwing summarizes cnsideratins in selecting mulches: Site Cntinual plant cver: trees, shrubs, perennials, and small fruit Annual sil preparatin: annual flwers and vegetables Nn-crp areas Specialty crps (rck garden, cacti garden, alpine garden Functin Sil imprvement ptential Frequency f reapplicatin Depth needed fr weed management Depth needed t minimize sil cmpactin Appearance Heat sink Off-site mvement by wind, water and gravity Safety (children, lawn mwers) Cst Lcal availability Cst f prduct Appearance Size f area t be treated (quantity needed) Depth f applicatin (quantity needed) Transprtatin csts Authrs: David Whiting (CSU Extensin, retired) with Carl Wilsn (CSU Extensin, retired), Catherine Mravec, and Jean Reeder, Ph.D. (USDA-ARS, retired). Revised by Eric Hammnd (CSU Extensin). Artwrk by David Whiting; used by permissin. Clrad Master Gardener GardenNtes are available nline at Clrad State University, U.S. Department f Agriculture and Clrad cunties cperating. Extensin prgrams are available t all withut discriminatin. N endrsement f prducts mentined is intended nr is criticism implied f prducts nt mentined. Cpyright Clrad State University Extensin. All Rights Reserved. CMG GardenNtes may be reprduced, withut change r additins, fr nnprfit educatinal use. Revised Octber 2014, December