Native nuts are highly sought after as a source of food by several species of wildlife. Examples of native nuts include acorns, hickory nuts, hazelnuts, Black walnuts, Butternuts and buckeye.
As it is very difficult to avoid loss and damage by wildlife when these are winter sown in pots outside, a cold stratification period in the fridge is a way to reduce winter losses.
Soon after collecting the nuts, remove the outer husks and discard any nuts with holes or other signs of insect or wildlife damage.
Insect damaged and dehydrated acorns and other nuts typically have some air space inside the shell and will tend to float when placed in water. So, by doing a “float test” where the nuts (with outer husks removed) are placed in a bucket of water, you can discard the nuts that float and plant only the tree nuts that sink. The ones that sink are the nuts which are less likely to be damaged or didn’t get too dry during the storage period.
Ideally, the cold period in the fridge will take you to springtime when the nuts can be taken out of the fridge, left at room temperature to sprout and then planted in pots and placed outside. If the nuts germinate before spring, they can be planted earlier but should be kept in a greenhouse, on a window sill or under grow lights until the conditions outdoors are more favourable to growth of young nut tree seedlings.
Note: Cold stratification of native nuts in the fridge should be damp and cold but not freezing (temperatures between 1-4 degrees C are recommended).
Instructions
Suggested growing steps include:
- Prepare the substrate for cold stratification of the nuts in a plastic bag (or zip lock bag). This can be damp vermiculite or a 50:50 mix of moist horticultural sand and peat moss. The substrate should be damp enough to hold its shape but not so wet that water drips out. Squeeze a handful to test the moisture; it should be the consistency of a sponge that has been wrung out.
- Place the nuts that have passed the “float test” in the bag leaving only a little air so the seeds can breathe.
- Make sure to label with the native tree name, date and where collected.
- The bag with nuts should be kept cool (but above zero) in the fridge or in a root cellar (not freezer) to mimic winter conditions for two to three months, until early spring when it can be taken out of the fridge and the nuts germinated or sprouted (at room temperature).
- To reduce moisture loss in the fridge, you can place the plastic bags with nuts in a large, sealed container (the kind used to store food in the fridge).
Check the moisture content of each bag monthly and re-dampen if necessary. According to one tree growing expert, Henry Kock (2016), finding a balance in moisture is the key. If the mix is too dry, the chemical reaction will stop. If it is too wet, the seeds will rot. Moisture should be that of a wrung-out sponge. - Once sprouted, the nuts can be planted in pots and placed outside in spring after the risk of frost has passed. Be sure to place a covering of protective screening over the pots or trays to reduce loss to digging and damage by hungry wildlife. It will be important to secure the protective cover over the pots or trays of nuts, either with rocks, bricks or clips.
- As with other young tree seedlings, they will grow best with limited sun exposure with some shade protection for the first two years.
References
Henry Kock 2016 Growing Trees from Seed : A Practical Guide to Growing Native Trees, Vines and Shrubs. Firefly Books. 288 pp.