This is spring in Minnesota. While we had some spectacular days near 80° in March, we had snow flurries and overnight temperatures below freezing in April. While we might think this is abnormal it’s probably because of our over anxious desire (need) to get outside and get working and planting in the garden. But the average last frost date in Minnesota is May 15 and I remember times when it snowed at the end of April and the beginning of May! Other than cool weather vegetables such as broccoli, cauliflower, peas and radish seeds, I recommend holding off planting any vegetable or annual flower seedlings until after May 15 and then only when the soil is sufficiently warmed. By mid to late May we should be ready to start planting all kinds of things and I am going to plant some summer flowering bulbs.
Summer flowering bulbs, also known as tender bulbs, include flowers that grow from bulb or bulb-like structures such as tubers, tuberous roots, rhizomes or corms. A tuber (dahlia) has a leathery skin and ‘eyes’ that grow into buds; rhizomes (iris) are an underground stem that grows at or near the surface; and a corm (gladiola) is a compressed stem that has a bud on top and contains stored food for the plant to grow. Unlike other bulbs (tulips hyacinths etc.) or rhizomes (irises), tender bulbs such as dahlias, tuberous begonias, gladiolas, cannas and calla lilies are not hardy in Zone 4. These bulbs are planted in the spring but they must be dug up and stored in a cool, dry place over the winter.
The best time to plant summer flowering bulbs is May 15 to June 15, but it’s dependent on conditions. The plants like warmth and bright light, so they should be planted in a sunny location once the soil has warmed. Alternatively they may be started indoors and planted outdoors once conditions are right. The ideal site would be one that receives plenty of sunlight and is sheltered from damaging winds; avoid low lying areas where standing water or frost might collect. Plant in well drained, rich soil from which all debris, such as rocks and sticks, has been removed. Add peat moss, finely shredded leaves or compost to create a good growing environment. If you do this no fertilizer is needed — our Minnesota soil contains an abundance of phosphorous which is a primary micronutrient needed to produce flowers.
Flowers are most attractive in mass plantings or planted in odd numbers. The planting depth and spacing is different for each bulb, so if you have package directions follow those. If not, the rule of thumb is to plant at a depth that is 2-3 times the diameter of the bulb; plant the base of the bulb at the appropriate depth with the point up. Depth can vary in different soil types; plant a little deeper in light, sandy soils and little more shallow in heavy clay soils.
Once you have placed the bulb(s) cover with half the soil, water, add the remaining soil and water some more. Then cover with mulch (leaf, wood or compost) to hold the moisture in and maintain an even temperature. If the spring/summer has less than normal rainfall keep the ground moist.
The bulbs can bloom any time from July through August — depending on the bulb, the cultivar and the time they are planted. If you would like to stagger the bloom times so that not all are blooming at once you could stagger your planting beginning in mid to late May and planting a few every week through mid-June. Or you could plant different cultivars which would have different bloom times. Smaller bulbs also bloom later than the large ones so you could plant various sizes to stagger the bloom times.
Once all the blooms are done cut off the stems only, leaving the leaves to produce energy (food) through photosynthesis to store in the bulb for next year’s flowers. Dig up the bulbs only after the foliage has dried up or been killed by frost. Dig several inches away from the base to avoid cutting roots or into the fleshy bulbs. Dig up the bulbs in clumps of soil, and then carefully clean off the bulb. Some bulbs like dahlias can be washed off gently with a hose, while other smaller more delicate bulbs or corms, like gladiolas, should be brushed off and left to dry. You should remove the ‘old’ corm and any little cormels. (These can be planted separately next spring although they may take several years to bloom.)
The bulbs should then be ‘cured ‘before storing: Set them in a dry, well ventilated place away from direct sunlight and drying winds; indoors if temperatures outside fall below 60°. One to three days is sufficient for most bulbs but gladiolas can be cured for as long as three weeks. Smaller plants can be stored in labeled paper bags. You can label larger bulbs (dahlias, cannas, etc.) by writing directly on the bulb. All should be stored in a cool (35°-45°) dry place –not in a refrigerator. Check the bulbs occasionally over the winter and remove any damaged or rotting material. This may sounds like a lot of work but you will be rewarded by some spectacular blooms in the years ahead.
“The amen of Nature is always a flower” – Oliver Wendell Holmes