Trees need reg­u­lar main­te­nance to ensure their long-term health and safe­ty in our land­scapes. The urban envi­ron­ment is the source of many stres­sors on trees; from asphalt reflect­ing excess heat, to the salt we put down in the win­ter time. Trees do not usu­al­ly encounter these stress­es in their nat­ur­al envi­ron­ment and they can often lead to poor growth or even death of the tree if they aren’t prop­er­ly addressed. There are lots of things we can do to help our urban trees grow large and live long, pro­duc­tive lives.

Keep your trees healthy with these practices.


The sin­gle most ben­e­fi­cial thing you can do for any tree
is to mulch it properly.

Mulching is the appli­ca­tion of mate­r­i­al on the ground in an area where plants are grow­ing. Var­i­ous mate­ri­als can be used accord­ing to the desired outcome.

In nat­ur­al set­tings, trees drop their leaves and branch­es right around them­selves and then re-absorb these nutri­ents as they are bro­ken down by microbes, ani­mals and oth­er organ­isms and turned into soil.

In the city, we plant trees in what are fre­quent­ly com­pact­ed, unnat­ur­al soils and we rake away all of the leaf mate­r­i­al before it has a chance to break down and improve the soil. Mulch improves the tree’s liv­ing con­di­tions in the city. It breaks down to pro­vide nutri­ents for the tree, while also yield­ing a host of oth­er ben­e­fits includ­ing pro­tec­tion from weed-wack­ers and lawn­mow­ers and retain­ing mois­ture in the soil.

How much should I mulch? 

The more space you are able to mulch, the bet­ter for your tree. Some land­scape stan­dards call for mulching to the ‘drip line’ of the tree, or to the edge of the tree’s leaf canopy. This may be imprac­ti­cal if you have a large tree in your yard whose canopy spans the entire lawn, so a small­er cir­cle of mulch around your tree may be more appro­pri­ate. The larg­er your mulch area, the greater long-term improve­ment in tree health and growth.

Street trees plant­ed in 3‑by-10-foot tree pits (stan­dard Pitts­burgh tree pits) receive the most ben­e­fit from mulching the entire 30 square foot area.

How thick of a mulch lay­er should I apply? 

Mulch wide, not deep, and do not allow mulch to touch the trunk of the tree.
Tree roots need oxy­gen, and if the mulch lay­er is too thick it can lim­it the amount of oxy­gen avail­able to the roots below. There­fore, lim­it the thick­ness of mulch around trees to a max­i­mum of 3 inches.

It is extreme­ly impor­tant NOT to pile any mulch up against the trunk of the tree. Even though this mis­guid­ed prac­tice is wide­spread in the land­scape indus­try, it will cause decay in the bark of your tree and can kill a young tree after only a few years.

What kind of mate­r­i­al should I use? 

Tree Pitts­burgh uses strict­ly hard­wood mulch. This is a local prod­uct made up of old trees, wood pal­lets, saw mill waste, and oth­er recy­cled wood that has been chipped up into small pieces. This mate­r­i­al breaks down at a good pace and stays put when applied in tree pits. Pine bark mulch is okay, but tends to wash out of tree pits too easily.

We do not rec­om­mend cypress or rub­ber mulch.

Cypress mulch is not a sus­tain­able prod­uct and should be avoid­ed. Cypress trees are removed from around the Gulf of Mex­i­co, and hur­ri­cane-prone areas suf­fer greater dam­age in storms as each one is removed.

Rub­ber mulch does not pro­vide many of the ben­e­fits men­tioned above. It will not decom­pose and will remain mixed with the soil for many, many years. There is spec­u­la­tion that rub­ber mulch may absorb heat and cause dam­age to the tree.

Plants for the Shade
(Good for Newly Established Trees)

Annu­als (plants that last one year and must be plant­ed annually) 
  • Bego­nia (Ele­gant flow­ers that come in a large variety)
  • Coleus (Var­ie­gat­ed foliage, pur­ple flowers)
  • Lobelia (Small edg­ing plant)
  • Pan­sy (Some are win­ter hardy)
  • Vio­la Tore­nia (Looks like a small pansy)
  • Impa­tiens (Pop­u­lar col­or­ful flow­ers that will do well in your tree pit, sun or shade)
  • Mon­key Flower Mimu­lus (A vari­ety of col­or­ful flowers)
  • Browal­lia (Fab­u­lous blue color)
  • Fuch­sia (Vari­ety of species, most annu­als bear a red tubu­lar flower)
Peren­ni­als (plants that come back year after year) 
  • Elephant’s ears Berge­nia cordi­fo­lia (Holds good win­ter color)
  • Coral Bells Heuchera
  • Spot­ted Dead­net­tle Lami­um mac­u­la­tum (Excel­lent groundcover)
  • Lily­turf Liri­ope mus­cari (ever­green)
  • Foam Flower Tiarel­la cordi­fo­lia (Vig­or­ous ground­cov­er with white upright flow­ers)Plant sug­ges­tions for tree pit gar­dens came from the New York City Parks & Recre­ation Web­site.

Plants for the Sun
(Good for Newly Planted Trees)

Annu­als (plants that live only one year and need to plant­ed annually) 
  • Sweet Alyssum (Mat form­ing, small yel­low or white flowers)
  • Dusty Miller – Senecio cinerara (Beau­ti­ful snow white and shiny sil­ver color)
  • Licorice Plant Helichrysum
  • Marigold
  • Nas­tur­tium
  • Por­tu­la­ca-Rock Rose, Moss Rose (Good drought-tol­er­ant plant)
  • Ver­be­na
  • Gera­ni­um (An old stand­by that requires lit­tle water)
  • Scent­ed Gera­ni­um (For leaf form, col­or and small flowers)
  • Salvia
  • Snap­drag­on
  • Heliotrope (Beau­ti­ful scent)
  • Cos­mos (Dwarf – height 24”)
  • Ager­a­tum (Low grow­ing with small pur­ple flowers)
  • Blue Mar­guerite Daisy
  • Lan­tana (A vari­ety of unique flowers)
  • New Guinea Impatiens
Peren­ni­als (plants that live for more than one year) 
  • Ox-eye Daisy chrysan­th­num leu­can­the­mum (Beau­ti­ful white flowers)
  • Bugle­weed Aju­ga reptans
  • Snow in Sum­mer Cerastium tomemtosum
  • Lily­turf Liri­ope muscari
  • Sedum Sedum albuonor acre (Only low growing)
  • Thyme Thy­mus ser­pi­phyl­lu­ur or pseudolanugip­sus (Mat form­ing varieties)

Tree Pit Gardening

When a new tree is plant­ed in front of a home or busi­ness, 30 square feet of new plant­i­ng space comes with it in the tree pit. Peren­ni­als, annu­als, and bulbs are beau­ti­ful addi­tions to a tree pit, as long as you remem­ber that the tree’s health comes first. Well-main­tained tree pit gar­dens bright­en up the pub­lic right of way along your block, through­out the neigh­bor­hood and in busi­ness districts.

(Dis­claimer: the City of Pitts­burgh requires an encroach­ment per­mit for any­thing plant­ed or installed in the right-of-way. While this rule has not been enforced for gar­dens, Tree Pitts­burgh wants you to be aware of it. Every tree plant­ed in the right-of-way has an encroach­ment per­mit already.)

Tree Pit Gardens 
  • Can dis­suade dog own­ers from let­ting dogs relieve them­selves in a tree pit.
  • Serve as reminders to own­ers to water the plants and the tree that was recent­ly planted.
  • Pre­vent cyclists from lock­ing bikes to a new­ly plant­ed tree.
  • Look great!

Guide­lines for Tree Pit Gardening:

  • Do not plant vines or plants that will creep up the tree trunk or onto branches.
  • Plant at least one foot away from the tree’s trunk to avoid dis­turb­ing the roots.
  • Plant shal­low root­ed plants that won’t com­pete with the tree’s nutrients.
  • Remem­ber to water the tree pit enough so that both the plants and the tree get water!
  • Con­sid­er the needs of pedes­tri­ans and peo­ple exit­ing parked cars. If your tree pit is next to a park­ing space that is not exclu­sive to you, do not plant large items that would act as obsta­cles to those exit­ing vehi­cles. Also con­sid­er plac­ing pavers or oth­er flat stones in the tree pit. Not only does this give peo­ple a com­fort­able place to step across, but it reduces the amount of com­paction that the soil will expe­ri­ence by being fre­quent­ly stepped on.

Tree Pit Approved Plants

  • Choose plants that require lit­tle water­ing. Key words to look for are “drought tol­er­ant” and “xeric conditions.”
  • Use small plants and bulbs – large plants require large plant­i­ng holes, which dam­age tree roots. In addi­tion, plants with large root sys­tems com­pete with the tree for water and nutrients.
  • Do not add more soil to your tree pit. Rais­ing the soil lev­el will harm the tree.
  • Mulching a tree pit is always good for your tree and plants. Mulch keeps the soil moist and pre­vents weeds from sprout­ing in tree pits.
  • NEVER PLANT: Bam­boo, Ivy, Vines, Woody Shrubs, Ever­greens or Inva­sives! They are all major com­peti­tors for water and nutri­ents and can stunt or kill a tree. See a list of inva­sives in Penn­syl­va­nia here (


Bulbs are a nice addi­tion to tree pits, and neigh­bor­hoods often plant them in the fall dur­ing tree plant­i­ngs. Many bulbs will return each spring, bring­ing col­or to your neigh­bor­hood. They are both afford­able and easy to plant.


New­ly plant­ed trees have often lost much of their root sys­tem dur­ing the trans­plant­i­ng process, leav­ing them high­ly vul­ner­a­ble to dying from drought dur­ing their first few sea­sons in the ground. It is very impor­tant for us to water trees when they are young to help them become estab­lished in the land­scape. Once they are estab­lished, they will have grown new roots out into the sur­round­ing soil, enabling them to col­lect enough water on their own that sup­ple­men­tal irri­ga­tion is not nec­es­sary. How­ev­er, even estab­lished trees can suf­fer dur­ing peri­ods of pro­longed heat and drought so always keep your trees in mind when water­ing the gar­den and give them a drink if you think they might need it.

Know­ing how much water to give a tree can be tricky, so fol­low these tips in order to keep your tree hap­py and healthy:

  • Give a tree 10 gal­lons of water each week dur­ing the grow­ing sea­son for every 1 inch of truck diam­e­ter at the time of plant­i­ng. For exam­ple, if you plant a tree whose trunk is 2 inch­es in diam­e­ter at the time of plant­i­ng, you would give it 20 gal­lons of water per week dur­ing the length of the grow­ing season.
  • Water a tree for one year for every one inch of trunk diam­e­ter at the time of plant­i­ng. For exam­ple, if you plant a tree whose trunk is 2 inch­es in diam­e­ter, it will need to be watered for 2 grow­ing sea­sons after planting.
  • Water slow­ly to ensure the water per­co­lates down through the soil to where the roots need it the most.
  • Con­sid­er your tree’s loca­tion and envi­ron­men­tal con­di­tions when water­ing. For exam­ple, trees in windy loca­tions will under­go more evap­o­tran­spi­ra­tion from their leaves, caus­ing them to need more water than trees in shel­tered locations.
  • Check the soil to deter­mine your tree’s water­ing needs. By dig­ging down a few inch­es, it is pos­si­ble to see if the soil has mois­ture in it or is very dry.

Winter Maintenance

Win­ter Tree Care 

Win­ter can be a harsh sea­son for new­ly plant­ed trees. Take a lit­tle bit of care with your trees this win­ter so that they will be nice and healthy in the spring.

Give trees fresh mulch in the fall. A new lay­er of mulch, kept away from the trunk of the tree in the shape of a donut, insu­lates the tree’s roots dur­ing the cold­est months. If you missed giv­ing your trees new mulch this fall, be sure to give them fresh mulch in the spring.

Be Care­ful with De-icing Prod­ucts. Rock salt (sodi­um chlo­ride), or de-icing mix­es that con­tain rock salt, pro­hibits a tree’s fin­er roots from absorb­ing water, nutri­ents and oxy­gen. If a tree’s soil receives a lot of salt in the win­ter, the tree will like­ly suf­fer in the spring and could poten­tial­ly die. Alter­na­tive prod­ucts such as cal­ci­um or mag­ne­sium chlo­ride are less harsh on the tree’s roots but can still cause harm if used exces­sive­ly. Fol­low these tips to avoid salt dam­age to your trees:

  • Use the rec­om­mend­ed amount of prod­uct. Many peo­ple over-apply de-icing prod­ucts in hopes that it will do a bet­ter job of melt­ing ice. Often the ice is melt­ed at the same rate but the excess prod­uct finds its way into tree pits.
  • Be care­ful when spread­ing the de-icing prod­uct. When apply­ing de-icers along the side­walk, be sure to avoid spread­ing prod­uct onto the soil of a tree pit.
  • If shov­el­ing salty slush off of the side­walk, do not pile it on tree pits.
  • If you live near a busy road that is fre­quent­ly salt­ed, con­sid­er installing a tem­po­rary bar­ri­er made of burlap or plas­tic to block salt from being sprayed into your tree pit by pass­ing vehicles.

Remove hol­i­day lights when the sea­son ends, and do so care­ful­ly. Many trees set their buds for new leaves and flow­ers in the fall, so be care­ful not to knock the new buds off branch­es when putting lights up or tak­ing them off the trees. Do not leave hol­i­day lights tied around trees year-round. Lights that are left on too long can end up stran­gling or “girdling” the tree, keep­ing nutri­ents from get­ting to its branch­es and killing it.

Prune Dead and Dam­aged Branch­es. Win­ter is a great time to prune as the trees are dor­mant and their struc­ture is easy to see. If you think now is a great time to prune your young street trees, con­tact Jake to sched­ule a prun­ing work­shop (

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