Tree Care

Watering

Trees give us so many gifts, including summertime cooling and shade, energy savings, community beautification, and improved human health outcomes. Even in a drought, trees are long-term investment worthy of water; your young trees need your help in order to stay healthy and thrive.  

It takes at least 2 to 3 years for your “drought tolerant” tree(s) to become established. After that, your tree(s) should not need additional watering during the dry season unless it’s extremely dry or hot. Follow the steps below to make sure your young tree(s) get the water they need. If you want to save water, try saving the warm-up water before you shower and giving it to the tree each week.  

RAINY SEASON (NOVEMBER TO APRIL):   

If we got at least 1/2" of rain in the past week, you can skip watering that week. If it has been more than a week since the last rain and the soil feels dry to you, give up to 15 gallons this week following the instructions below (see “Dry Season”).  

DRY SEASON (MAY TO OCTOBER):  

  • Watering bags: One option is to install a 15-gallon watering bag around the tree. During the dry season, find the hole near the handle and fill your watering bag to the top one time per week for the first 3 years. Mark your calendar for the same day each week, so you don't forget. The bag will slow-drip 15 gallons of water to the roots. The watering bags are meant to help your tree get established; for the health of the tree, please make sure to remove the watering bag after the first 2-3 years.  
  • Drip system: If you are using an existing drip system to water your trees, make sure the system is set to deliver 15 gallons once a week during the dry season (May-October), or as needed based on the “finger-test” described below. For example, if you have three 5 GPH emitters around your tree, you will need to run your irrigation for one hour once a week to deliver 15 gallons.  
  • “Finger Test” for overwatering: Before you are thinking of watering again, stick your finger 2" into the ground near the tree, and don't water if it feels wet. Too much water can be as bad as too little. When a tree is overwatered, the leaves will turn brown and fall off, which might make you think you're not giving enough water, and the problem will get worse if you give it even more.   
  • Clay soil: If you have clay soil, you may be able to water every 10-14 days instead of every week—it’s important to check with your fingers when you first start watering to figure out how quickly the water drains through your soil. Deep, infrequent watering will help your trees establish strong, deep root systems. Avoid giving a little water every day; it is not good for your tree.      

Mulch and fertilizer

  • Mulch: Put a layer of mulch (wood chips) over the rootball, like the leaf-litter in a natural forest. This layer insulates the roots from heat and cold, reduces evaporation of water, smothers weeds, and provides the ingredients for healthy soil. If you see that the mulch has been disturbed, just move it neatly back into place. Don't let mulch or soil touch the base of the trunk (“root crown”), because wet bark can rot and eventually kill the tree. Just brush it away from the trunk.  
  • Fertilizer: Do not use fertilizer, potting soil, or chemicals on your newly planted trees. These products can kill your young trees.  

Weeds and other plants 

Weeds: Please pull grass or other weeds growing inside the watering-ring (berm).  They take water and nutrients away from the tree. Pull by hand or with simple tools if you can, since weed-whackers can accidentally cut the tree's bark and hurt it.  

Additional Plants: It’s okay to plant flowers, perennials, or small shrubs around your new tree, but outside the watering-berm (ring), not within 2 feet of the trunk. These extra plants will be especially valuable if the soil has been under pavement for a long time. 

Stakes

Installed stakes protect your tree(s) against wind and accidental damage. The rubber or plastic strap should loosely encircle the trunk so that the tree can move in the wind without falling over.  Leave the stakes on for 3 years or until the trunk of the tree is at least 3" in diameter.   

Pruning

Most landscape trees will need corrective pruning eventually, but usually not in the first year or two. It’s best to get an expert’s advice before doing any pruning or removing any large branches. If you know proper pruning techniques, you may remove suckers, small broken branches, or small branches that interfere with walkways. Do not remove every leaf or small branch sprouting from the trunk.  

Free advice  

If you have tree health questions, you can contact the free Help Desk provided by the UC Master Gardener Program of Alameda County. This year-round resource can help you by researching tree issues and providing advice on all aspects of home gardening. Please note that the UC Master Gardener Program is not associated with the City and cannot answer City tree program specific questions.

UC Master Gardener Program of Alameda County website

Help Desk hours: M, W, TH, 10am-1pm 

Help Desk contact: 510-670-5645, [email protected]