Before exploring how to best grow your plumeria seeds and seedlings, start with the right seed. If you intend to grow for grafting rootstock or you want to grow a new cultivar, you should use the best quality plumeria seeds. Coming soon….Plumeria Seed Choices.
What Do Plumeria Seeds Need to Germinate?
Viable plumeria seeds are living entities. They must contain living, healthy embryonic tissue in order to germinate. All fully developed seeds contain an embryo, a store of food reserves, wrapped in a seed coat. Seeds generally “wake up” and germinate when soil moisture and temperature conditions are correct for them to grow.
Seeds Need the Right Environment to Germinate
Temperature, moisture, air, and light conditions must be correct for seeds to germinate. All seeds have optimal temperature ranges for germination. The minimum temperature is the lowest temperature at which seeds can germinate effectively. The maximum is the highest temperature at which seeds can germinate. Anything above or below this temperature can damage seeds or make them go into dormancy. At optimal temperatures, germination is rapid and uniform, for plumeria seeds usually 5-10 days.
Plumeria seeds need correct moisture to initiate internal processes leading up to germination. In soil, this is generally about 50-75 percent of capacity. A fine-textured seedbed and good seed-to-soil contact are necessary for optimal germination. Aeration in the soil media allows for good gas exchange between the germinating embryo and the soil. Seeds respire just like any other living organism. They need oxygen and produce carbon dioxide (CO2). This carbon dioxide needs to be able to move away from the seed. If the soil or media is not well aerated due to overwatering or compaction, the CO2 will not dissipate and seeds can suffocate.
Not all seeds have the same light requirements. Most seeds germinate best under dark conditions and might even be inhibited by light. Don’t confuse seed light requirements with what seedlings need. All seedlings require sunlight. Seedlings will become leggy and fragile and will not grow to their potential if they do not have sufficient light.
Soil temperature conditions for plumeria seed germination, Minimum (F) 60, Optimum Range (F) 75-95, Optimum (F) 85, Maximum (F) 95. Soil temperatures should be taken by inserting a soil thermometer 3-4 inches deep into the soil surface and noting the temperature.
For plumeria seeds to come out of dormancy, we have to break their physical dormancy factors. Plumeria seeds have a thick seed coat, The most common method is some form of soaking the seed in warm water. Others use scarifying (scratching the surface) the seed, artificially weakening the outer coat of the seed. Water and warm temperatures are the two factors that break plumeria dormancy.
There are several methods used to help test viability and germination of Plumeria seeds: Pre-Soaking in warm water, Soaking between paper towels overnight, soaking between paper towels in a plastic bag, planting directly into the soil, placing in styrofoam and floating in the water, planting directly into plugs, etc. They all work, the trick is to find out which method or combination of methods works best for you. Coming soon…Plumeria Seed Viability Test
Steps of Seed Germination
- Imbibition. The seed rapidly takes up water and the seed coat swells and softens. The outer seed coat becomes soft and wrinkly with water.
- Interim or lag phase. During this phase the seed activates its internal physiology, cells respire, and the seed starts to make proteins and metabolize its stores of food.
- The radicle and root emergence. The cells start to elongate and divide, bringing the root and radicle out of the seed.
To find out whether or not your seed is viable, do a germination test. Wrap seeds in a wet paper towel, place in a warm spot, wait 4 hours or overnight, and count how many seeds absorb water and plump up. The ones that plump up will most likely germinate.
If you save your seed from the year before, think about this: the life of a plumeria seed can be cut in half by an increase of just 1 percent in seed moisture or by an increase in storage temperature of just a few degrees. A simple rule of thumb is to store your seed in a dry cool place.
A study was done by Eulas Stafford with the Plumeria Society of America. He gathered a large quantity of Slaughter Pink seeds and proceeded to plant 10 seeds a year for 10 years. The results: The first two years 100% germinated and after that, an additional 10% failed to germinate each consecutive year. In the 10th year, only 1 germinated.
Early Seedling Development
Plumeria are Dicots (Two-seed Leaves)
The primary root, called the radicle, is the first thing to emerge from the seed. The primary root anchors the plant to the ground and allows it to start absorbing water. After the root absorbs water, the shoot emerges from the seed. In dicots, the shoot has three main parts: the cotyledons (seed leaves), the section of the shoot below the cotyledons (hypocotyl), and the section of shoot above the cotyledons (epicotyl). The way the shoot emerges from soil or growing media follows two main patterns. In plumeria, the section of the shoot below the cotyledons elongates and forms a hook, pulling the cotyledons and the growing tip through the soil. Once it reaches the surface, it straightens and pulls the cotyledons and shoot the tip of the growing seedlings into the air. This is called epigeous germination.
After the shoot emerges, the seedling grows slowly while the storage tissue of the seed diminishes. Soon, the plant develops a branched root system or taproot. Then, true leaves that look like the leaves of the mature plumeria appear. These leaves, unlike cotyledons, photosynthesize light into energy, allowing the plant to grow and develop. When the true leaves start converting light into energy, the seedling needs a source of nutrients.
Managing for Optimal Germination and Seedling Development
We know that plumeria seeds need optimal amounts of water, oxygen, and temperature to germinate. If we don’t create the most optimal environment possible, then plants tend to germinate slowly and unevenly. Generally, space is limited, so we want plants to germinate as quickly as possible. Uneven germination can also cause problems. If you have ever had to transplant a flat of seedlings where half are ready to plant and the other half are too small with root balls that don’t slide easily out of their cells, you will understand why. Damage to roots can cause a setback in the growth of the seedling.
One common option to achieve optimal germination temperature in growing media is to use germination mats. These mats allow you to set the temperature according to seed requirements. For example, plumeria will germinate in 7 days at 86°F, but take more than 15 days to germinate at 65°F.
Make sure you maintain optimal temperatures for your plumeria. It is also critical to promote air circulation to mitigate fungal pathogens such as those causing damping off.
The optimal temperature for growing seedlings may be different from that for seeds. Remember, the optimal temperature will stimulate optimal growth. Cooler temperatures generally slow down growth, and warmer ones speed up growth.
Temperature and time required for growing Plumeria seedlings to transplanting size. Day (F) 70-90, Night (F) 60-70, Time (weeks) 2-4
It is still critical to maintain good air circulation and sufficient moisture. Generally, watering should be deeper to accommodate developing root systems. Remember to carefully monitor and water the plants at the edges of flats. They dry out faster than those in the middle. However, overwatering can increase the probability of plumeria developing damping off.
Over the last four years, I’ve been experimenting with different media for seeds and seedlings. I’ve determined the use of FlexiPlugs to be the best choice for my projects. They give me the ability to water as much as 3 times a day and they still provide adequate oxygen to the roots. They also hold nutrients and provide the best way I’ve found to allow transplanting with minimum root damage. More…Starting Seedlings in Plugs