Answer: After six years you should have seen an increase! In my experience, the larger and better quality of the bulb you start with, the faster they multiply.
The better the planting site, the faster they multiply -- this would be good rich soil that is evenly moist yet well drained while they are actively growing but dry in the summer and also well drained in the winter. Excess moisture in winter is probably the biggest factor in losing them or not seeing the increase you should. The other main factor is which varieties you are growing, some are less adaptable than others.
Here are some things I have learned about them through trial and error. The site really needs to be nice and sunny in the spring when the foliage is growing, too. Allowing the foliage to grow is also critical because this is how the plant restores its energy to keep growing. Fertilizing when they are active in the fall to help them root and then again in very early spring can help. I would also top dress with a good quality compost and if they are in planted beds, top with aa few inches of an organic mulch year round. This will also help feed the soil on an ongoing basis as it rots down.
I have many naturalized daffodils at home and one thing I discovered is that it can be worth the trouble to deadhead them so that they direct their energy back to the bulbs rather than to seed production. This will cause the original bulbs to muiltiply by splitting so that you have more blooms at the site where you originally planted each bulb.
On the other hand, allowing them to set seed results in seedlings, assuming the weather that year was favorable. This approach really increases the number of plants in a hurry -- you will have scads of baby plants all around each original where the seeds fell. These babies will need several years to reach blooming size however, and under less than ideal conditions it seems to take forever. They may also be crowded and need transplanting so they have enough space to grow, mature and thrive.
The other important factor is which varieties you are growing. Some simply seem to thrive year in and year out and mulitply happily while others fade away. When you shop for them, look for those that include "multiply freely" or "good naturalizer" or similar wording in the variety description. For me, Ice Follies, Tete a Tete, King Alfred and Carlton plus a no-name box of transplants dug from a neighbor have done especially well. Mount Hood is said to be a good one for this but it has not increased as much, nor has Barret Browning. To some extent this may reflect the native soil and growing conditions where they are planted so some may do better for you and worse for me for example. I have found that dividing clumps of the ones that really thrive will continue to yield generously more of the same for me if replanted in a similar location.
I know you have already researched this but The American Daffodil Society includes some great tips on naturalizing at their web site and suggests additional varieties at
I hope this helps you trouble shoot.
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