ACORNS TO OAKS
How to Grow Your Own Oak Trees
The historical and economic importance of Iowa's oaks led the General Assembly to name them the state tree in 1961. But considering how desired oaks are, a landscaping trees it is surprising how infrequently they are planted for that purpose. Partly this is because oaks are slow growing and can take as long as two to three decades before they begin to provide significant shade. But mostly it's because the oaks, with their deep penetrating tap roots, do not fit into the current commercial nursery practice of supplying large caliper (trunk diameter) balled and burlaped or container grown trees for planting.
Bur oaks can send a tap root down as deep as five feet in the first year of growth. If about 95% of a tree's roots are removed when it's moved from the nursery then oaks do not make good candidates for transplanting. The best and fastest growing oaks are grown in place--starting exactly where they'll end up. This is what nature does when white oak acorns sprout after falling to the ground or when red oak acorns buried by squirrels sprout and grow the following spring.
We can also grow perfectly good oaks by directly planting acorns. Not all of these acorns will sprout however, and some may be dug up by squirrels and birds. Others might be nibbled off by rabbits and deer after sprouting. Once up they'd have to compete with existing vegetation, roots, and shade. A better way to insure success is to grow our own seedlings and give them the proper attention they need at every step of their growth cycle. The goal of this booklet is to show you how to select and store acorns and then turn them into strong and healthy trees. It's easy. It's fun. And it will cost you little or nothing to produce these valuable trees.
The oaks of Iowa can be divided into two groups: the reds (subgenus Erythrobalanus) and the whites (subgenus Leucobalanus). The red group includes red, pin, black, Hill's, blackjack, and shingle oaks. Distinct features of those in the red group include the short bristle tip on each leaf or leaf lobe, velvety inner surfaces on acorn shells, and the fact that acorns require two growing seasons to mature and do not germinate until the spring following dispersal.
The white oak group includes the white, bur, chinkapin, swamp white, and post oaks. The lobes or teeth of the white group do not have bristles and are generally round, the inner surface of acorn caps is smooth, and the acorns germinate shortly after they hit the ground in autumn.
There is also an important difference between the wood of the red and white oak groups. The pores of white oak are blocked with small plugs (tyloses> that make the wood watertight and thus valuable for use in cooperage (barrel making). Federal law requires that all domestic whiskey be aged in casks made from white oak. Red oak has open pores and white oak is not as valuable in cooperage is used extensively for finish limber, flooring, furniture, and railroad ties. All of the oaks are valuable sources of fuel wood.
The most commonly available oak at commercial nurseries is the pin oak and large numbers of these trees have been planted in recent years. But this oak is no longer recommended by most arborists because of problems with chlorosis--a condition of leaf yellowing caused by nutrient deficiencies related to soil alkalinity. We would like to see you plant white, bur, swamp white, and red oaks instead.
Choose swollen or plump-looking, mature acorns from healthy trees and pick them off the ground as soon as possible. Whites start sprouting soon after they fall--even if it has started its shoot, you can still collect it.
Put acorns in a plastic bag with an equal amount of leaf mold or peat mix and barley dampen. Close the bag loosely and store in the refrigerator at between 32 to 35 degrees (whites will continue to sprout at between 36 and 39 degrees). Check acorns throughout the winter and keep just barely damp. Acorns need about 1000 hours of low temperature dormancy. Plan to plant your acorns in late April from the 15th to the 20th. You can leave them in the refrigerator and plant as late as July, but an early start will produce stronger seedlings.
Plant Your Seed
Do not use garden dirt since it packs and may carry diseases. Use a good quality potting soil mixed with the same amount of milled sphangnum moss. You want a porous, sponge-like soil. Take an 8 ounce styrofoam cup and punch three to four pencil-sized holes in the sides next to the bottom. Fill to the top and tap to settle the soil leaving about an inch watering space. Place the acorn horizontally, barely under the surface. Water until it comes out the bottom and place cups on a southern windowsill. Never let the soil get completely dry, always prime first and water until it drains. Check moisture daily or more often if necessary.
In about three weeks the stalk will be five to six inches and the first set of leaves will have spread. About mid-May it is time to harden the plants off. Gradually increase exposure time to outside sun and air. Set the trees outside during the day and return them to house or garage at night.
Be careful off late frosts and remember that deer, rabbits, chipmunks, and ground squirrels will be more than happy to eat your tender seedlings. You may need to fence them from the sides and top to protect them from these competitors. Arrange your trays in such a way the wind won't blow over your seedlings.
Around late May you can transplant to a 16 ounce cup. Check to see if roots are curling around the bottom of the 8 ounce cups.
Remember to punch drain holes and use a mix of half potting soil and half leaf mold from the forest floor or leaf compost. Settle the mix by tapping again and leave one inch watering space after transplanting the seedling. Now your trees can be kept outside all the time, but be sure to check them for drying out in sun and wind. Keep them damp. You can use a mild solution of Miracle Grow or a similar fertilizer when watering at this stage.
Second Flush of Leaves
With the second flush of leaves your seedlings can be transplanted into a 32 ounce, tall, food container. Check the taproot and see if it is bending around the bottom of the cup before transplanting. White and healthy-looking roots are a sign of vigor. Use the same soil mix and provide drain holes. The larger container will hold moisture longer but be sure to check it regularly.
Pests and Problems
Check for aphids and wash them off or sue a paint brush to remove them. If June bugs eat the leaves, keep plants in the garage at night until July. Warm, humid, muggy days with cool nights may spawn powdery mildew. Use a commercial fungicide. If the soil becomes too dry or if you notice leaf spots or brown margins, submerge the plant completely in water until the bubbles stop. This will leach soluble salts and fertilizer from the soil, preventing the burning of root ends which can kill the plant.
Planting Your Trees
You can plant your young oaks in the fall or overwinter and plant them the following spring. To overwinter, keep them in a garage, enclosed porch or basement at temperatures between 5 to 45 degrees, with 20 to 30 degrees the best. Don't let temperatures get below zero at the root. Plants need 1000 to 15000 hours between these temperatures. Even in winter, check the moisture level and keep just barely damp.
Remember to protect young trees by caging them--even the tops if you have deer browse. Water your trees in dry weather and give them a light mulch to retain moisture and keep weeds down. Remember that oaks will eventually be big trees, so don't plant them too close to buildings, sidewalks, or driveways.
If you start planting oaks now, as a young person, you will be able to bring your children and grandchildren to sit under and enjoy these trees. As you grow and mature, your trees will be growing and maturing too. You can enjoy these trees throughout your life and know that future generations will appreciate your thoughtfulness. White oaks can live as long as 500 years!