How deep bulbs should be planted – and why they go deeper – Daily Press

Q I read your advice on planting amaryllis bulbs outdoors (March 5) and I disagree with one point. As someone who has grown and crossed them outdoors for about 25 years in Hampton, I plant mature bulbs outdoors here below or at ground level. If necks are exposed to hard frost, most will die. It is best to cover the necks with peat moss or leaves each fall. I dig and replant about every five years or so for overcrowding, and because they tend to pop out of the ground.

Now a question. Daffodils do something evolutionarily bizarre. Every year they sink deeper into the ground. Eventually, they cannot flower or divide. I found them alone and over 18 inches deep in a friend’s yard! From an evolutionary perspective, that doesn’t make a good trait to pass on. What is happening here? —C. Heightes, Hampton

A. Thank you for writing with your experience and question. If you have found that planting your amaryllis at this depth is best for you, in your area and in your conditions, I certainly wouldn’t try to argue with that. However, the consensus in most horticultural circles is that amaryllis should be planted with the nose slightly out. I think your tips for mulching them are spot on. In colder regions, this makes good sense. No need to deviate from a method that has been proven for over 25 years.

For all bulbs, the general rule is that they should be planted two to three times their length or height. But the optimum planting depth is known to vary somewhat by species. Additionally, the optimal depth may vary within a species, depending on environmental conditions such as humidity. It has long been observed that bulbs can move vertically over time, as you mentioned.

In 2007, Mordecai Jaffe and Carl Leopold of Cornell University noted in the Journal of the American Society for Horticultural Science that bulbs such as tulips and lilies, when planted too shallow, “sink “deeper into the ground. Gardeners like you have known for a long time. But for years, the couple had been studying the physiology of the bulb’s contractile roots, which are responsible for movement. The bulb they chose to study was the Easter lily, variety Nellie White, which I grew for many years in the greenhouses of Tidewater Community College for Easter. The researchers concluded that the bulbs received their cues from light – the blue wavelengths of the spectrum, which stimulated the formation of contractile roots, causing the bulbs to move downward.

Other wavelengths in the spectrum were not effective. This suggested the presence of a blue light absorbing pigment in the bulb or leaves involved. Interestingly, the researchers also observed that the blue light did not affect the roots and the response decreased with age and with deeper planted bulbs.

So why all this? The researchers postulated that this adaptation allowed the bulbs to descend to a protected depth, where conditions would tend to be more constant. Leopold said he had lily bulbs that over the course of a decade had sunk an entire foot. As you noted, at greater depths they eventually stop blooming and dividing. Another reader recently wrote that over the past 50 years his daffodils have multiplied many times over. There aren’t many blooming anymore, and she’s tired of dividing them.

It sounds like a particular evolutionary strategy that would leave a person without the ability to procreate. But it may be one of many strategies that work simultaneously. The “go deep” strategy would provide a constant and favorable environment. It might also provide some protection from predators, such as squirrels. The “strength in numbers” strategy is similar to trees that produce prodigious pollen, seeds and fruit. That’s what’s happening right now: check your car’s windshield. It is intended to overcome all the obstacles that exist. Daffodils, however, produce annual waves of vegetative offsets. Alas, as with tree seedlings, there are only a small fraction of resources to support. Only the strong survive.

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