Edibles Grow Sheets

Walnut

• Scientific Name

  English/Persian: Juglans regia; Northern California Black: Juglans hindsii; ‘Paradox’: J.hindsii x J. regia
• General Information

  

  Photo: Roman Odintsov, pexels

  Large, fast-growing, deciduous tree 40 to 80 feet tall. Called English/Persian, or Northern California Black or the hybrid ‘Paradox’. The delicious, nutritious walnut we eat is actually the seed of a drupe, a fleshy fruit with thin skin and center stone containing a seed. Good choice for Marin’s hottest micro-climates. Can live for centuries.

• When to Plant

  Most commonly planted as bare root trees grafted on rootstock, typically available in nurseries mid-December to mid-January. Plant immediately or keep moist in sand or sawdust outside until it's planted. 

  To grow from seed:

  1. Collect walnuts after they fall to the ground.
  2. Remove husks and place in water. Good, usable nuts will sink to the bottom.
  3. Discard any nuts that float. 
  4. Plant one to two inches deep in the ground in fall. (Walnuts must be exposed to cold temperatures and moist conditions to germinate.)
  5. The cold-moist requirement can also be achieved through a process called stratification. For this, keep the nuts moist in a coffee can or food storage container. Keep just above freezing for 90 to 120 days by placing in the refrigerator. Once the walnuts have been stratified, they can be planted.
• Planting

  Choose the sunniest spot in your garden that is relatively sheltered from the wind and has 30 to 60 feet of spacing to allow room for the tree to grow. 

  Dig a hole at least twice the diameter of the container (use two feet as a guide if bare root tree did not come in a container), with a depth of two inches less than the distance between the crown and the root ball. The two inch depth difference will ensure the plant sits slightly higher than the soil line. Shape the hole with slightly sloping sides. Gently untangle the roots, removing any shoots within six inches of soil, and place the root ball on firm soil to avoid settling, and spread out the roots. Fill with original soil and create a water basin away from the trunk. Apply a thin layer of organic matter/mulch three inches away from the trunk.

  Important: do not plant near other plants. Walnuts produce a growth inhibitor that can negatively affect plants growing nearby.

• Soil Requirements

  Plant in deep, well-drained, permeable soil (at least five to six feet) with pH between 6-7.

• Water Requirements

  After planting in winter/spring and watering initially, use rainfall as a guide to keep the soil moist. Young small trees need four to 12 gallons of water per day; larger trees require approximately 20 to 40 gallons per day. Water deeply and slowly, away from the trunk, every three to four weeks through the summer months; or drip irrigate daily May to October using a drip line set away from the trunk for more frequent watering. Avoid wetting the leaves. Walnut trees require regular irrigation for a quality nut crop, but once established can tolerate periods of drought.

   

• Fertilizing

  When first planting a bare root tree, just add a little top dressing compost. The second year, a healthy dose of compost around the base of the tree (away from the trunk) in the spring will meet the tree's nitrogen needs. Fertilize three plus year-old trees in early spring with five to seven pounds of urea or 90 to 150 pounds of manure. Sprinkle beneath the canopy, one and a half feet away from the trunk.

• Pollination

  Pollinated by wind. Walnuts are monoecious (separate male and female flowers on one tree) and dichogamous (pollen is shed when female flowers are not receptive). Thus, two different varieties must be planted to ensure overlapping bloom periods, fertilization, and fruit set. Pollen from a different variety of the same type of tree – a pollinizer - increases pollination, and therefore, improves production.

   

• Harvesting

  When the outer green fleshy layer of the nut (hull) begins to break away from the shell, normally from mid-September to early November, nuts are fully mature. Harvest nuts by poling (literally using a long stick or pole to knock nuts off the tree onto the ground) or picking up the ones that have fallen on the ground as soon as possible to avoid pests infiltrating the nuts. Hull walnuts as soon as possible after harvesting and wash the nuts after hulling. Wear gloves when hulling as walnuts contain phenols that stain and irritate hands. Dry the hulled, in-shell walnuts in a shady area with air circulation and warm summer temperatures. Walnuts will dry in three to four days.

   

• Storage

  Store shelled or un-shelled walnuts in an airtight container in a cool, dry place. For longer-term storage, place shelled walnuts in plastic freezer bags in the refrigerator for up to three months (away from smelly foods), or in the freezer for up to a year. If fall weather has been wet, ensure walnuts are dry before storing. Nuts can be put on a tray in the sun for a day or two to release extra moisture. (Conventionally, walnuts are dried in gas dryers for 24 hours or less, until the nuts reach eight percent moisture content.)

• Good Varieties for Marin

  'Chandler': a UC-patented cultivar and most widely planted commercial cultivar. Pollinizer is 'Franquette'. 

  'Pedro': smaller-sized variety

  'Robert Livermore': dark red walnut skin

  'Howard': pollinizer is 'Mayette'
  
  'Tehama': pollinizer is 'Mayette'

• Helpful Tips

  Wear gloves when removing the green hulls as they can stain your hands. Keep the tree area free from weeds while becoming established. Young trees are intolerant of competition, especially from grass or lawn. Keep tree base dry to reduce crown rot problems. Do not plant near other plants, as walnuts produce a growth inhibitor. Consider spraying tree with dormant oil (a petroleum/water product that suffocates pests) if scale (a sucking insect) is an issue. 

  Prune to keep a more manageable size or choose a smaller variety.

  Winter – prune trees by thinning out crowded areas to let light into tree.  Spray trees with dormant oil to control scale insects, if needed.

  Spring – remove all weeds from the tree base to reduce competition and pest problems.  Fertilize.

  Summer – Keep tree base dry to reduce crown rot problems, ensuring drip line or watering is away from the trunk.

  Fall – Harvest, and if nuts fall on their own, pick up as soon as possible.

• Common Problems

  Poor harvest – walnut trees need regular water, hot temperatures, and, optimally, a pollinator nearby

  Crown gall – caused by a soil bacteria that causes large, irregular growths at the base of the tree. These galls reduce the flow of water and nutrients.

  Walnut blight – a bacterial disease that causes black lesions on catkins (flowers), side of nuts, leaves or shoots.  Most common in wet and humid spring conditions

  Frost damage -- Young trees are susceptible.  Prune off damage in summer.

• Pests- Diseases & More

  Learn more.

  Learn more about growing walnuts.