Pinus strobiformis seed
Botanical Name: Pinus strobiformis
Subspecies: SOUTHWESTERN WHITE PINE
Common Name: Pinus strobiformis, SOUTHWESTERN WHITE PINE, Mexican white pine, Chihuahua white pine
Minimum Hardiness Zone: 5
Pinus Strobiformis (southwestern white pine)
Pinus Strobiformis seeds have a deep dormancy within them, this requires a degree of patience to overcome and it is usually quite easy to get high levels of germination if the correct procedures are followed.
First prepare a free draining substrate into which the seeds are to be mixed, this can be a 50/50 mixture of compost and sharp sand, or perlite, vermiculite or even just pure sharp sand. The chosen substrate needs to be moist (but not wet), if you can squeeze water out of it with your hand it is too wet and your seeds may drown and die.
Mix the seeds into the substrate, making sure that their is enough volume of material to keep the seeds separated. Place themixture into a clear plastic bag (freezer bags, especially zip lock bags are very useful for this -provided a little gap is left in the seal for air exchange) If it is not a zip-lock type bag it needs to be loosely tied.
Write the date on the bag so that you know when the pre-treatment was started.
The seeds first require a period of warm pre-treatment and need to be kept in temperatures of 20 Celsius (68F) for a period of at least 8 weeks During this time make sure that the pre-treatment medium does not dry out at any stage or it will be ineffective!
For the final part of the breaking of the dormancy the mixed seeds need to be kept in the fridge for around 12 weeks.
One this is complete the seeds are ready to be sown.
Fill your chosen container with a good quality general potting compost. Suitable containers could be plant pots, seed trays or plug trays or even improvised containers with drainage holes. Firm the compost gently and sow the seeds on the surface. If you are sowing in plug trays, sow 1 or 2 seed per cell.
Cover the seeds with a couple of millimetres of vermiculite or failing that a fine layer of sieved compost. Follow with a gentle watering and keep them at room temperature. Germination will begin a few weeks from sowing.
The seedlings are reasonably robust and trouble free and usually grow to a height of between 5 and 12 cm in the first growing season depending on the sowing date and cultural techniques. Densely sown seedlings are at risk from fungal diseases such as “damping off” which can cause rapid loss of many seedlings.
Developing seedlings should be fine in full sun, keep them well watered and free of competing weeds. Growth will accelerate in the second and subsequent years and the developing young trees should be re-potted as necessary preferably during the dormant season. After 2 or 3 years they are ready to be planted in their permanent position.