Growing an oak tree from an acorn is a rewarding project that begins long before the seed reaches the soil. Acorns are classified as recalcitrant seeds, meaning they cannot tolerate drying out and must be kept moist until germination. The survival of the potential sapling depends entirely on managing the acorn’s moisture content and temperature during the period between collection and planting. This careful management ensures the seed is ready to sprout when spring arrives.
Initial Selection and Cleaning
Acorns should be collected in early to mid-autumn, shortly after they naturally fall from the tree, as these nuts have reached full maturity. Inspecting for physical damage is the first step; discard any acorns with visible holes, which indicate a weevil infestation, or those that appear cracked, shriveled, or moldy. Weevil larvae feed inside the acorn, creating a cavity that makes the seed non-viable.
A simple and effective way to test viability is the float test, where acorns are submerged in a container of water. Healthy, dense, and viable acorns will absorb water and sink to the bottom. Acorns that float are usually non-viable because they are either dried out, undeveloped, or contain internal air pockets from pest damage. Since some viable acorns may float initially due to slight dehydration, soaking them for up to 24 hours can help them rehydrate and sink. After selection, the acorns should be surface-dried for an hour or two to remove excess moisture before being placed into storage.
Understanding Dormancy and Stratification
Acorn species fall into two main groups, which dictates their storage and planting requirements: the white oak group and the red oak group. White oak acorns lack a natural dormancy period and are ready to germinate almost immediately after falling in the autumn. If not planted right away, white oak acorns will often begin to sprout in storage and must be handled with care.
In contrast, red oak acorns require a period of cold, moist conditions to break their internal dormancy. This process, called stratification, mimics the natural cold of winter and is necessary to trigger germination readiness in the spring. Without this chilling period, red oak acorns will not sprout when planted.
Practical Cold Storage Methods
The goal of cold storage is to provide the necessary cool, moist environment for red oak stratification and to maintain the viability of both red and white oak acorns until spring planting. The ideal storage temperature range is just above freezing, between 34 and 40 degrees Fahrenheit (1 to 5 degrees Celsius), typically achieved in a standard refrigerator. Temperatures that are too high will encourage premature germination and mold, while temperatures that are too low may cause damage.
To maintain the required moisture, acorns are stored in a medium that holds water without becoming waterlogged. Suitable materials include damp peat moss, sand, or a mixture of the two. The medium should be moist enough that a squeezed handful releases only a few drops of water. This prevents the acorns from drying out, which is a common cause of seed death.
The acorns and medium should be placed inside a container that allows for some air exchange to prevent the buildup of mold and excessive moisture, such as a sturdy plastic bag with small ventilation holes or a container with an open top. For red oak acorns, the stratification period generally requires a minimum of 30 to 90 days. Check the stored acorns periodically for any signs of mold or premature sprouting, removing any affected nuts to prevent contamination.
Planting the Stored Acorns
Acorns are ready for planting when they show signs of successful stratification, most notably the emergence of the radicle, which is the embryonic root. This small, delicate root is the first part of the seedling to emerge, and it should be handled with care to avoid breaking the tip. The optimal time to transition the stratified acorns from cold storage to their final location is in the early spring, coinciding with the end of the natural frost period.
When planting, the acorn should be placed no deeper than one to two inches below the soil surface. The proper orientation involves placing the acorn on its side, or with the radicle pointing downward if one has emerged. Planting the nut sideways allows the emerging root to grow naturally downward and the shoot to grow upward. Immediate protection is necessary following planting, as squirrels, mice, and other animals are attracted to the freshly buried acorns. Covering the area with a physical barrier, such as a wire mesh or hardware cloth cage, can prevent the seed from being dug up.