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I spoke with Jo-Ann van den Berg-Ohms from Van Engelen Bulb Company the other day. Her family has been in the Dutch bulb business for five generations, so I trust her advice when it comes to bulbs.
She noted that bulbs are best planted once soil temperatures cool to about 55 degrees, so she tells people to wait and plant bulbs until we have had at least two weeks of sweater weather. If it is too cool outside without a jacket then it's just right for planting bulbs.
So what do our spring and summer bulbs need in a year's worth of growth and care? Well, at planting time we want a site that is rich and well drained, so the bulbs have soil where roots can easily develop and where water will not stand and cause rot. And at planting time we want cool soil.
Cool soil at planting time and an adequate chilling time before bloom is necessary for the hardy bulbs that most of us will choose for Kentuckiana gardens. Cool soil in fall allows the bulb to stay sleepy while developing some roots before the weather turns cold.
Once the roots have anchored the bulb in the ground then it rests. Often a restful chilling period of at least 10 weeks is necessary for some bulbs to bloom. Reputable bulb companies send you premium-sized bulbs that are rested and chilled; cheap bulb companies do not always set you up so well.
When the soil begins to warm in the spring, the bulbs responds by putting out more roots and top growth. Some bulbs need warmer soils then others, but the fact remains the same: Once growth starts the stored energy from the previous season is now being expended at a rather brisk rate.
Once the bulb blooms we sometimes lose interest, but it is extremely important to leave the plant to its own devices. The growth of foliage and the photosynthesis that occurs after blooming is the only way the bulb can store enough energy for the following year.
Do not braid, fold or cut away the foliage. Learn to love it, or your bulb display will decline over the years by your own hand, not natures!
Some bulbs are known for their ability to persist for years; others are not. Daffodils, species tulips, scilla, galanthus, chiondoxa, leucojum, hyacinthoides, crocus, camassia, and Asiatic lilies are all garden staples that, if planted in the right location, will return year after year.
Some can be a bit more finicky. Most fancy tulips should be considered annuals: Enjoy the dramatic display the first year then rip them out or lower your expectation for the future.
Allium persist well for me in the garden but only if the soil is extremely well-drained. The Darwin hybrid tulips are reliable for several years; Fritillaria can be disappointing but F. meleagris (also known has Guinea hen flower or snake's head fritillary) proves the more reliable species for Kentuckiana;
I was always in the habit of sprinkling a little fertilizer concoction made from cottonseed meal, bone meal and alfalfa meal around my bulbs after they finish blooming in the spring or summer. To get the most from your bulbs, van den berg-Ohms suggests that we fertilize with a top dressing at planting time and then follow up with another round when the foliage begins to emerge, than again when the flowers fade.
If old bulbs seem too slow in their performance, then a little digging and dividing may be in order. As baby bulbs form, they crowd and compete for nutrients and moisture, so dig later in the summer ,once all bulbs have gone dormant. Sort them, reserving the healthiest, and replant after you have worn your sweater outside for about two weeks.