Considerations for Collecting Tree Seeds for Plantings

Written by Jeff Osborne, Forest Stewardship Program Associate, James C. Finley Center for Private Forests at Penn State

Over the past two weeks, if you have been walking under oaks or hickories, you may have been struck by discarded pieces of acorns or hickory nuts as squirrels feed; and hopefully you were reminded that it is time to collect many types of seeds for planting. Collecting seeds for planting on your own property or to help benefit someone else’s planting project can be a great way to reconnect with the forest. There may even be a local conservation group that would accept seedlings that you grow from the seeds you collect. Often, they have their own nurseries to grow species that are more difficult to purchase from commercial nurseries and would benefit from the extra seedlings.

Many seeds commonly used in tree plantings are collected in late summer through fall, although some are collected from spring into summer. Many trees drop their seeds, or animals pull them off, over the course of a couple weeks, so it is important to know when to be on the lookout for target species. Some species, like those in the white oak group and some maples, begin to germinate shortly after falling, so they should be planted shortly after gathering. Many species wait until the following spring to germinate. These may require being held at a certain cold temperature for a period of time such as would occur over winter, also known as stratification. These species of seed can be planted in the ground in the fall, but they are often kept in refrigerated storage to reduce losses from animals eating them or from issues caused by too much or too little moisture that could occur from fall to spring. In the spring, late frosts can also kill seedlings that have just emerged. There are some other species that germinate only after their hard seed coat has been scarified (openings in the seed coat created) by chemical, or mechanical means, allowing the seeds to absorb water. Scarification can naturally occur as the seeds pass through the digestive system of animals or can be simulated by artificial means such as by sanding. The table below shows considerations for collecting seeds from several species, including collecting and planting season as well as whether seeds need to be stratified or scarified before they will germinate and grow.

Table 1. Seed collecting and planting times

There are many insect pests of seeds and there are climatic events that will cause seeds to not grow to maturity. As you are collecting larger seeds, like acorns, you can discard obviously damaged or malformed seeds. Several seeds, like acorns and white pine seeds, can be float tested in water. Floating seeds are likely to be unviable and should be discarded. Seeds that need to be cold stratified can be stratified in a refrigerator. If you do not have enough space there, there are other methods to stratify seeds in the ground that protect them from animals and manage the moisture to maximize germination in the spring.

Before you plant, you will want to consider where you plant the seeds and where their final planting site will be. If you are planting seeds that you are transporting for an early summer or fall planting, you may want to plant them in well-drained loamy soil in small pots, such as a 2”x2”x6-8” plastic pot. This pot will be large enough for most seedlings for one growing season. If you plan on transplanting seedlings less than 1 year old or planting seeds in their final rooting place, make sure your seed beds contain a well-drained, moist loamy soil. Seeds should be protected from small and large rodents, as they may dig up larger seeds even weeks after they have germinated in spring. Plant your seeds after the risk of frost passes. Monitor your seeds several times a week for soil moisture, evidence of pests like rodents, or microorganisms like Phytophthora. (Phytophthora is a genus of oomycetes, or water molds, that can spread quickly in wet, poorly drained soil and can quickly kill seedlings.) Many reputable sources provide in-depth species-specific collection and planting guides like this one for butternut, or results from studies, such as this one from the US Forest Service for Northern Red Oak. These references may be from around the US, and timing adjustments should be made based on local temperature.

If you are planning on collecting seeds to plant in an area more than a few miles away, you should consider the seed zone of both the collection site and the planting site. A seed zone is an area with similar topography and climate, and you can expect plants growing in the same seed zone to have similar tolerance for different environmental factors such as first and last frost, and minimum winter temperatures. It is a good idea to plant seeds in the same seed zones they were collected in, and record and keep track of where you collect the seeds in case problems arise later in the plantings. Many common garden research plantings, which contain a single species of seeds collected from all over its range, indicate that seeds collected from a seed zone that is very dissimilar from the garden zone do not perform as well as seeds collected from the same or similar zones. In some studies, the reduced competitiveness of these trees was not noticed until 20 to 30 years after they were planted. Based on the common garden findings and predictions that local climates will not be static, you may want to consider gathering seeds from the same seed zone and two similar zones for plantings. There was a recent effort, completed in 2020, to update seed zones in the US.

The map above shows the current seed zones in Pennsylvania (screen capture from the Eastern Seed Zones mapping project).                                                              There are currently nine seed zones.                                                                                                                                                                                 
Seed zone 5 is the only zone that is entirely within the borders of the state.                                                                                                                                           
The map for the US can be explored at  http://www.easternseedzones.com/map                                                                                                                                                                                                                                                                                                                                                                               
So, the next time a walnut hits you on the forehead, you should remember this article and some of the considerations you should take if you want to plant that walnut, or other seeds, on your property or elsewhere.