The purpose of grafting is for controlled consolidation and pollination of specimens. This allows the genetics of LSAs to be replicated in home or group orchards for easier maintenance, pollination and controlled crossing.
There are many grafting techniques, but we have mainly utilized the epicotyl method. A sprouted seed’s main shoot is clipped off just above the nut. The stem is split lengthwise, creating a slot for the scion to be matched. The scion is shaved down, slid into the slot, matching the cambium layers (vascular tissues).
The wound is wrapped tightly with parafilm (grafting tape), which maintains contact between the tissue and also reduces water loss. The seedling is placed in a plastic bag, where the roots provide energy and nutrients for the scion to mate and grow. If all goes well a new set of leaves emerge and the above ground portion of the plant is an exact clone as the tree the scion was collected from. The seedling is nurtured in the bag, with high humidity over several weeks, before hardening off and transferred to a pot or bed.
Video of grafting technique.
Post Grafting Steps
Success rate varies depending on scion source. Last year I had some sources with 10% success rate and others were 75%, but average was about 50%. I lost an additional 10% of grafts during the hardening off process, so when in doubt err on the side of patience. The below guidelines and timelines and not hard and fast rules as all conditions and environments vary.
- Keep bags nearly fully sealed to maintain 100% humidity. A small amount of air circulation is ideal to hold off mold. Maintain temperature at 65-75 degrees. Chestnut grafts are sensitive to cold and the graft will not take. A germination heat mat can be used to provide bottom heat if desired.
- Successful grafts should push buds and leaf out in 2-4 weeks.
- Keep bags under grow lights or in partial indoor sunshine as they grow and humidity is adjusted. They need light for photosynthesis, but are sensitive and can burn.
- About a week after leaves have emerged, begin hardening off with humidity changes. Day 1: open bag for 15 min, then close. Day 2: 30 min, Day 3: 1hr, Day 4: 2hrs, Day 5: 4hrs. Day 6: leave the bag zipper slightly open without closing. Day 7: quarter open. Day 8-9: half way. Days 10-14: fully open.
- After the two weeks a successful graft should be calloused over, however it is still fragile. It is time to remove the seedlings from the bag and transplant them into pots. The nut has provided energy to the growing seedling and can be carefully removed with scissors, without cutting the root or stem. This will reduce predation from squirrels. Don’t underestimate them. If you have labeled your seedlings be sure to transfer the labels so you can keep track of the source genetics. Parafilm will degrade with UV exposure, however I typically will gently remove it during this stage. Other film types will not degrade and can girdle the tree if not removed.
- For growing tips check out the growing techniques tab on the ACofM website. Do not use standard potting soil without modification and try to pick a deep pot to allow tap root development.
- Your baby tree is very sensitive to sunlight and wind and should be hardened off very slowly. I’ve found they actually grow better their first year under shade cloth vs full sun.
“How Can I Get Involved Further?”
1)Dougherty Mission House/Tree Volunteer List-Contact Tom twdalluge@gmail.com
2)Join The American Chestnut Foundation (TACF.org)
3)Join American Chestnut Restoration (americanchestnut.org)
5) If you’re curious and want to participate in the LSA breeding program contact Ben below.
If you have any questions please reach out at americanchestnutsofmichigan@gmail.com
Thank you for participating and caring about the American Chestnut.
American Chestnuts of Michigan 