Spring is the correct time to plant geophytes, which are plants with underground storage organs (bulbs, corms, tubers, and rhizomes). These structures hold the necessary energy for the plant to grow and flower, producing vibrant blooms throughout the summer and into the fall season. Summer-flowering varieties require the warmth of spring soil to initiate growth, unlike their cold-tolerant counterparts.
Distinguishing Spring-Planted and Fall-Planted Bulbs
Spring-planted varieties, often called “tender” bulbs, are native to tropical or subtropical regions and cannot withstand freezing temperatures in the ground. Gardeners plant them after the final spring frost has passed to capitalize on warmer soil and the extended growing season. These bulbs, like Gladiolus corms or Dahlia tubers, develop roots and foliage through the late spring and summer before producing flowers.
Fall-planted bulbs are considered “hardy” because they are adapted to survive cold soil temperatures. These include popular choices like tulips, daffodils, and hyacinths. Their successful springtime bloom depends on a mandatory, prolonged chilling period, known as vernalization, which breaks dormancy and triggers flower bud formation. They are planted in autumn to establish roots before the ground freezes, using the winter cold as the necessary biological cue for their spring display.
Top Recommendations for Summer-Blooming Bulbs
Dahlias, which grow from tuberous roots, provide one of the longest bloom seasons, typically flowering from mid-summer until the first hard frost. Their mature size is highly variable, ranging from compact 1-foot bedding varieties to towering 6-foot dinner-plate types. All varieties demand a location that receives a minimum of six to eight hours of direct sunlight daily. Most Dahlias will begin to show their first blooms approximately 90 days after planting.
Gladiolus, grown from corms, are known for their spectacular vertical flower spikes that can reach heights of two to five feet. These “sword lilies” require full sun exposure and well-drained soil. They typically bloom 70 to 100 days after the corms are placed in the ground. For a continuous supply of cut flowers, gardeners often stagger the planting of corms every two weeks throughout the spring.
Tuberous Begonias prefer partial shade or filtered light, making them perfect for containers and shaded garden beds. They grow from tubers and produce large, showy flowers, sometimes up to six inches across, from late spring until cold weather arrives. Their mature height usually stays under 18 inches. They require protection from intense afternoon sun to prevent leaf scorch.
Canna Lilies grow from rhizomes and bring a tropical feel with their large, paddle-shaped leaves and tall, vibrant flower stalks. Depending on the cultivar, these plants can range dramatically in height from a compact 1.5 feet to over 10 feet in a single season. Cannas thrive best in full sun, needing at least six to eight hours of direct light to support their foliage and ensure consistent blooming from mid-summer to fall.
Essential Steps for Successful Planting
Timing the planting correctly should only occur after the final expected frost. The soil temperature must be consistently warm, ideally reaching at least 60 degrees Fahrenheit, to prevent the underground structures from rotting. Planting in cold soil can lead to delayed emergence or complete failure, as these tender geophytes are not adapted to cool, damp conditions.
Proper soil preparation ensures the bulbs have the necessary environment for root development and growth. All summer-flowering bulbs require excellent drainage, so amending heavy clay soil with organic matter like compost or aged manure is beneficial. This aeration prevents water from pooling around the storage organs, which is a common cause of fungal disease and decay.
A general guideline for planting depth is to bury the bulb or tuber at a depth equal to two to three times its vertical height. For example, a two-inch tall Gladiolus corm should be planted four to six inches deep, with the pointed end facing upward. Adequate spacing is also necessary, as crowding restricts air circulation and encourages the spread of mildew. Larger varieties like Dahlias may need up to three feet of distance between each plant.
Ongoing Care and Maintenance Through the Growing Season
Once the geophytes have sprouted and begun to actively grow, consistent moisture is a primary requirement for robust foliage and bloom production. While newly planted bulbs should not be watered until shoots appear, established plants need deep, regular watering, especially during dry periods. The goal is to keep the soil consistently moist but never waterlogged, which is particularly true for Canna Lilies that prefer slightly wetter conditions.
Fertilization should be managed carefully to promote flowers over excessive leaf growth, especially for Dahlias. These plants benefit from a fertilizer with a lower nitrogen content, applied every three to four weeks, to encourage bud formation. Tuberous Begonias and Canna Lilies respond well to a balanced, slow-release fertilizer applied once in the spring and again mid-summer.
Taller varieties, such as many Gladiolus and larger-flowered Dahlias, require structural support to prevent heavy blooms from snapping the stems. Placing stakes or cages near the plant at the time of planting ensures the support system is in place before the foliage is too dense to work around. Providing this support early protects the plant’s vascular structure and maintains the integrity of the flower spikes.
Preparing Tender Bulbs for Winter Storage
Since most summer-blooming geophytes are not cold-hardy in temperate climates, they must be dug up and stored indoors before the ground freezes. The process should begin shortly after the first light frost, which signals the end of the growing season and causes the foliage to wither and blacken. This minor frost exposure prompts the plant to transfer remaining energy reserves back into the underground storage organ.
The foliage should be cut back to a short stub (typically one to six inches) before carefully lifting the bulbs, corms, or tubers from the ground with a garden fork. Avoid nicking or bruising the storage organs, as damaged areas are highly susceptible to rot during dormancy. Excess soil should be gently removed, but the structures should not be washed, as surface moisture increases the risk of fungal infection.
A crucial next step is curing the geophytes by allowing them to dry in a cool, dark, and well-ventilated location for several days or up to two weeks. This curing process toughens the outer skin, creating a protective barrier against moisture loss and pathogens during storage.
Once cured, the bulbs should be nested in a medium like peat moss, vermiculite, or dry sawdust within a breathable container, such as a cardboard box or mesh bag. The ideal storage location maintains a cool temperature between 40 and 50 degrees Fahrenheit and remains dry. This ensures the geophytes stay dormant and viable until they can be replanted the following spring.