Plants are rooted in a simple bulb structure. They flower in mid- to late spring (April through June) and go dormant by summer. Bulbs should be planted in autumn. As a member of the Fritillaria genus that includes species classified as toxic to humans and animals, F. imperialis should be planted out of the reach of children, dogs, and cats. Crown imperial plants are pretty much impervious to any issues but the bulbs have a tricky shape that needs some special attention. The top of each bulb has a notch from where the plant eventually emerges. This notch can easily collect water and cause the bulb to rot, so although it needs to be planted upwards in the soil, it should be done so on a slight angle to avoid the problem. Once you buy your bulbs in the early autumn, plant them immediately, as they do not like to be out in the air for long and easily dry out and/or rot. Bulbs should be planted 6 to 8 inches deep. If you want, you can incorporate bonemeal and a 10-10-10 fertilizer into the soil to give the bulbs their best chance of success, although this isn’t strictly necessary. Bulbs should be planted between 9 and 12 inches apart in groups of between 6 to 12. Cover your bulbs with a thick layer of mulch after they are planted and backfilled with soil.
Light
Crown imperial prefers full sun (6 to 8 hours of sun per day) and will also grow in semi-shade, woodland conditions.
Soil
Overall, the crown imperial is flexible in its ability to grow in a variety of soils from medium (loamy) to heavy (clay) that range from a pH of acid, neutral, or alkaline. Native to locations such as the Himalayas and Turkey, it is most happy grown on cliffs and rocky slopes in well-drained soil.
Water
Water only when plants are actively growing in the spring. Give them about one inch of water per week if it does not rain. Take care to keep only the top six inches of soil moderately moist as the crown imperial does not need an excessive amount of water and can tolerate drought.
Temperature and Humidity
Crown imperials are tough plants and can survive in a range of humidity levels and temperatures. The bulbs, in fact, are tolerant to temperatures as low as -30 degrees Fahrenheit.
Fertilizer
You’ll want to give your crown imperials an organic fertilizer in the spring, and then a diluted liquid fertilizer in the fall. For the amount to use, follow the product label instructions. In autumn, add one inch of compost on top of the bed and two inches of mulch to insulate the bulbs and keep weeds down.
Types of Crown Imperial
There are many varieties of this showy plant, with names that are almost as striking as the flowers they produce—including several that honor famous composers. Fritillaria imperialis ‘Maxima Lutea’ is perhaps the most popular variety. Its flowers are yellow, creating a crown distinctively dramatic in form. Fritillaria imperialis ‘Aurora’ has orange-red flowers. It grows 2 to 3 feet tall and is hardy from USA zones 5a to 8b. Fritillaria imperialis ‘The Premier’ has flowers of a softer orange akin to the shade of a tangerine, with light-purple veins. It grows between 24 and 36 inches tall. Fritillaria imperialis ‘Aureomarginata’ displays an even softer shade of orange blooms and dual-colored green-golden foliage similar to a spider plant. It grows up to 36 inches tall. Fritillaria imperialis ‘Rubra Maxima’ offers a distinct orange-red that looks caramelized and nearly burnt. Flowers are shaped like human eyes, covered with long pistils and stamen. This plant grows between 40 to 44 inches. Fritillaria imperialis ‘Brahms’ has salmon-pink flowers, and unlike other varieties, it does not have the scent to deter rodents and voles. Fritillaria imperialis ‘Beethoven’ is a dwarf variety growing about 2 feet tall. It has creamy orange flowers that grow atop a purple base and is especially sensitive to water-retentive soil. Fritillaria Imperialis ‘Bach’ is another dwarf variety growing only an average of 2 feet tall. Flowers are red with nuanced shades of orange. In addition to the usual ability to deter deer and rodents, the Bach attracts bees like many other bee-friendly flowers you can welcome into the garden.
Pruning
In summer, the foliage will go dormant. Trim off spent flowers but leave the foliage on the plant so that it can send energy to the bulb for the next season’s growth.
Propagating Crown Imperial
Every three to five years in the late summer or early fall depending on your climate zone (August in the lower end of the zone spectrum), dig up all the mature bulbs, separate, and replant them. This not only produces new plants, it also helps the plants continue to thrive and put on a flower-rich show season after season.
Growing Crown Imperial From Seeds
Growing crown imperial from seeds that you collected from your own plant requires quite a bit of effort yet it will likely have disappointing results, as germination is erratic, and most crown imperials are cultivars whose seeds do not produce plants that are true to the parent. Cultivar seeds are not widely available. If you would like to propagate the plant, it is best to start with bulbs from the division of an existing mature plant.
Potting and Repotting
Crown imperials don’t do well in containers; they should be grown in garden soil or raised beds that provide the necessary depth and allows them to grow undisturbed for a long period of time.
Overwintering
The plants do not need any winter protection, as their foliage has already died back during the summer. If you live in a very mild climate, dig up the bulbs in the early winter and bring them inside. After they are thoroughly dried, store them in the refrigerator for 4 to 6 weeks before replanting them in the ground in early spring. This mimics the natural period of cold temperatures that the bulbs need to spur them into another cycle of growth.
Common Pests and Plant Diseases
This plant is truly resistant to most common diseases and pesky invaders. One thing to watch out for is invasion by scarlet lily beetles which will eat holes in the leaves. Unfortunately, the same insecticides that work on these beetles also harm the plant, so a better strategy is to remove the bugs by hand and/or to set up glue traps around the plant.
How to Get Crown Imperial to Bloom
The striking bell-shaped flowers of this plant reach their full size and color display when situated in full sun. The plant can grow in partial shade as well, but this will lead to duller and smaller blooms. If the plant is not flowering in the first year, it could be that the soil needs a bloom-boosting fertilizer that is high in phosphorus and potassium.
