Plants from Seed

    Before describing the methods I use to grow native plants from seed, I should describe myself. I am an impatient person. Perhaps, this is why I only became interested in plants later in life. I was a zoologist by education and training; a person more interested in moving things than stationary ones. I have the greatest admiration and amazement for people like my friend, Anna Palomino, and others who can wait month after month for a tray of seeds to sprout. I cannot. This is why I so frequently use techniques such as scarification to induce germination. And, while these methods are frequently effective, one should not begin to assume they are natural. In fact, the research of Carol & Jerry Baskin (https://bio.as.uky.edu/users/ccbask0) and others suggest scarification and other shortcuts are not the natural means of germination for many of the seeds that respond to these methods. So, why use germination shortcuts? I’m impatient.

Why grow from seed? 

There are three reasons to prefer growing your native plants from seed. First, only seedlings, not cuttings or air-layers, develop a taproot. A taproot can be important for firmly securing the plant in the ground and for accessing deep moisture sources. Tree species, in particular, are far less likely to topple if they are grown from seed than from cuttings. Out in Kalaeloa where it is very dry and the water table is about ten feet below the ground, I discovered that naio and naupaka grown from seed survived much better than those grown from cuttings if they were not watered after their initial planting; cutting-derived plants required several months of supplemental irrigation to match the seed-derived plant survival percentage. Second, only with seed is each plant a unique genetic individual. In a garden setting this may not be important, maybe, not even desirable. But, for a field restoration project, genetic diversity is all-important in order to maximize the chances of the new colony surviving the myriad of environmental variables. You can use cuttings from many genetically distinct parent plants – if you have them. But, often you don’t. You may have only a handful of parent plants to start the new colony. Growing from seed (along with the cuttings from the parent plants you do have) will yield the greatest genetic diversity possible. Third, in Hawai‘i, most native plants naturally propagate themselves via seed. By propagating your own native plants from seed, you can learn about this natural process. Perhaps, even learning something that will prove crucial to understanding why the plant is becoming rare in nature or how we can maximize our success in germinating a limited seed supply from a now-dead plant or extinct colony.

There is more than one correct way to grow native plants from seed.

Nearly every native plant horticulturist has his or her favorite techniques for growing native Hawaiian plants. Some prefer to place the seeds in a tray of media under a mist system. Others prefer agar-filled petri-dishes. Still others plant each seed in its own individual pot and hand-water until germination. Below, I describe how I prepare seeds prior to planting, my three preferred methods of sowing seeds, and the germination shortcut treatments I often use.

Preparing seeds for sowing 

Depending upon the plant, I may have to wash away the fleshy fruit from a seed(s) or extract the seed(s) from a dry fruit capsule or chamber. Regardless, I never sow fruits, with two exceptions: (1) plants with a stony endocarp like naio, in which case, I treat the endocarp as a seed, and (2) plants like Achyranthes and hinahina kū kahakai with very small seeds that are very difficult to separate from a surrounding thin dry fruit. After cleaning the seeds with water, I sterilize their outer surface by soaking the seeds in a 10% bleach solution for approximately 15 minutes. (Be certain to stir the solution several times so all the seeds’ surfaces are exposed to the bleach.) I then rinse the seeds several times in water to remove the bleach and allow the seeds to air dry. If I plan on storing the seeds, I place them in a labeled (i.e., species, date, collection site, number of parent plants, number of seeds) paper envelope and place the envelope in a refrigerator. If I intend to sow them, I use a variety of methods to speed or enhance their germination (see below). Which method I use is based on previous experience or readings, or is the beginning of an experiment. For specific species, you should go to that species webpage to discover which method I prefer.

Soaking 

Prior to sowing any seed, I soak it in tapwater for at least a day. The water should just cover the seed in order to maximize gas exchange with the air above; submerging the seed in several inches of static water could potentially suffocate the embryo. Lately, I’ve been soaking seeds for periods longer than a day, sometimes, with surprising results. For example, the four ‘akoko species I’ve grown (Chamaesyce celastroides, C. degeneri, C. kuwaleana, C. skottsbergii) all begin to germinate in the shallow water after a few days (see ‘Ewa Plains ‘Akoko for photograph of germinating seeds). Similarly, species such as maua (Xylosma hawaiiense) germinate quicker and in greater synchrony if I soak them for about one week before sowing. If you decide to soak your seeds for longer than a day, be sure to gently wash the seeds and change the water at least once every day. This will deter the growth of water-loving fungi that might harm the seeds. The longest I’ve ever soaked seeds before sowing is two weeks.

Gibberellic Acid

Today there’s lots of information readily available about gibberellic acid (GA) on the Internet so I will not go into details of its discovery, history in research and horticulture, etc. Suffice to say, GA is a naturally-occurring chemical (actually, many different types of gibberellins have been discovered) found in plants that, in low concentrations, promotes seed germination in some species. 

    My interest in using GA began with experiments to quicken and synchronize the germination of ‘iliahi (sandalwood). Later, I discovered it was also effective on Scaevola species (naupaka). Based on earlier studies by others and my experiments, I settled on treating seeds with a 0.05% - 0.1% solution of GA (i.e., 50 - 100 mg per 100 mL). I normally soak the seeds in a shallow GA solution in the same manner as I soak seeds in tapwater (see above) for five or more days. After 1-3 days of soaking, I discard the old solution, gently wash the seeds, and place the seeds back in a fresh GA solution. Since GA affects embryo metabolism, you want to make sure the GA is actually getting to the embryo. Therefore, for seeds with a thick seedcoat or surrounding endocarp such as ‘iliahi, I scar the seeds before soaking. 

    You can buy GA online from several suppliers. I generally buy a small amount (i.e., 1-10 g) of highly concentrated powder (e.g., 90%) and store it in my freezer rather than buying premade solutions that have a limited shelf-life. Because GA is effective at very low concentrations, making GA solutions requires a sensitive scale to accurately weigh out the GA. Fortunately, metric scales accurate to 1 mg (0.001 g) are much cheaper today ($100 or less) than they were back when I started my GA experiments. Unfortunately, this decrease in price is most likely due to the illegal drug market. (It’s probably best to just smile and laugh when visitors to your home or nursery see the scale and think you might be supplementing your income by selling drugs.) The GA normally takes some time and stirring to dissolve completely. You can hasten this by first dissolving the GA in a very small volume of alcohol before adding water to achieve the correct concentration of solution.