Determining when to move Plumeria seedlings outdoors involves assessing several factors to ensure they are ready for the transition and that outdoor conditions are suitable. Here are key indicators and considerations to help you make this decision:

1. Seedling Maturity: Plumeria seedlings should be well-established before they are moved outside. This typically means they have several sets of true leaves (not just the initial sprout leaves) and have developed a sturdy stem. This process usually takes a few months after germination.
2. Size of the Seedlings: Generally, Plumeria seedlings should be at least 6-8 inches tall and have a robust root system. This size indicates that they are strong enough to handle outdoor conditions.
3. Outdoor Temperature: Plumeria is a tropical plant and sensitive to cold. Ensure that outdoor temperatures are consistently above 50°F (10°C), both day and night. The ideal time is often late spring or early summer, after the last frost date in your area.
4. Hardening Off: Before permanently moving them outdoors, Plumeria seedlings need to be gradually acclimatized to outdoor conditions, a process known as “hardening off.” Start by placing the seedlings outside in a shaded, protected area for a few hours each day, gradually increasing their exposure to sunlight and outdoor temperatures over a week or two. This process reduces transplant shock.
5. Weather Conditions: Avoid moving seedlings outside on windy days or when extreme weather is expected. Choose a mild, calm day for the transition.
6. Preparation of Outdoor Site: Prepare the area where the seedlings will be placed. If they will be in pots, ensure the pots have good drainage. If they are to be planted in the ground, choose a spot with well-draining soil and adequate sunlight.
7. Overall Health: The seedlings should be healthy and free from pests and diseases. Weak or sickly plants may not survive the transition.
8. Sunlight Exposure: Plumeria plants love sunlight. Ensure the area where you plan to move them gets plenty of sunlight, at least 6 hours of direct sunlight per day.
9. Soil Readiness: Whether planting in pots or the ground, ensure the soil is well-draining. Plumeria does not like ‘wet feet’ and can suffer from root rot in soggy soil.
10. Wind Protection: If possible, choose a location that is protected from strong winds, as Plumeria seedlings can be quite delicate.

By carefully assessing these factors and preparing both the seedlings and the outdoor environment, you can successfully transition your Plumeria seedlings outdoors, setting them up for continued growth and eventual blooming.