Delphiniums: A Lover To Manage

In last week’s column I told you of my long love affair with delphiniums. It has not been a smoothly going affair, and before you try to establish a relationship with this plant my goal is that you do so with both an open heart and open eyes.First, keep in mind that I’m writing about the tall type of English delphiniums that are most common in our gardens and landscapes. Some buy them in large gallon or larger pots fully budded and treat them as annuals in their gardens. That’s fine but not really necessary once you learn how to manage this plant.

However, there are also other types of delphiniums that are smaller, less hardy but also find a place in many gardens, containers and pots. There is also a plant referred to as the annual delphinium or larkspur, but this short look-alike is not really a delphinium, though the flowers can look similar. There are actually 300 species of delphiniums, and while the majority of them are perennial (though many not reliably hardy here), there are also several biennials. For this reason you need to look at the variety you are buying and make sure it’s an elatum or an elatum hybrid, as those are the ones most likely to be hardy.

My relationship with this plant has been tempered by two facts of life or at least two facts of a delphinium’s life in our area. While the elatum varieties, which include all of the taller garden delphiniums and the taller hybrids, are said to be hardy to zone 4, there is a caveat with that hardiness. Remember that hardiness applies not only to how cold it gets but also how warm it gets, and when we have very warm and humid summers these plants seem to suffer. So it’s very possible for these plants to survive in our gardens for a year to several years but there is a good chance that sooner or later they may succumb not to cold, but to heat and humidity. For this reason I consider them to be somewhat short-lived perennials, though you may find otherwise.

The second fact of life for these delphiniums is that there is an insect that may be a problem. Technically it’s not an insect since it has eight legs and not the requisite six to be a true insect, but we still refer to them as insects. It’s actually quite tiny and you will never see it with your naked eye, but its damage is unmistakable. It’s called the cyclamen mite, Phytonemus pallidus, and it was first discovered in Jamaica, Queens, in 1898 on some chrysanthemums. It was thought to have been brought into the country on some cyclamen corms, and it’s been with us ever since.

This mite thrives in warm and humid conditions, so when it gets warm out here in the summer its reproduction rates skyrocket. Later in the season it overwinters in the egg stage, only to re-emerge the following spring in small numbers until the weather gets warm and humid again. But since it is a mite and not a true insect, it is not affected by many of our common insecticides and by the time we notice that it’s around, so much damage has been done that the plants often have to be destroyed. Remember that this mite is tiny, so we realize its around only if we monitor our plants (with a 10x loupe) or see the symptoms.

On a delphinium the symptoms are very classic. The foliage begins to curl and become distorted. Newly emerging foliage is distorted. Flowers that emerge can be misshapen and the mite’s feeding results in a condition that is referred to as the “blacks.” Black spots show up on the foliage or entire leaves may turn black and black splotches may show up on the stems as well.

So, what’s a gardener to do? What I’ve learned from others who love this plant is that if you want the best tall delphiniums in your garden you grow them for three years, then take a three-year hiatus. This seems to disrupt the cyclamen mite population and reproduction to a point where they can reasonably be controlled. It’s hard love and it’s been a long three years for me but there’s no other garden plant like it and this is a road I’m willing to travel.

For those wanting to try another route I have another prescription. First, when you buy your delphiniums inspect them for the mites or symptoms. This has to be done with a 10x loupe or good magnifying glass. The mites are light shy, so you’ll find them only on the undersides of the foliage. If you feel the plant is mite-free, then plant it, but during the growing season continue to monitor it for mites or symptoms. Spraying a very light horticultural oil such as Pure Spray can also be very effective, as it smothers both the eggs and adults. Oil sprays should be applied only on cool days and it’s important to cover the stems and undersides of the foliage with the spray and reapply several times during the summer.

Whatever you do, don’t use any insecticide you pick up off the self or from the garden shed or garage. There are actually some insecticides that will result in increases in the mite populations. On the other hand, there is one very effective insecticide (actually miticide) that can be used, and that’s abamectin, which is sold under the trade name Avid. It’s not cheap and will cost nearly $100 for just 8 ounces, and it has to be used with caution as the mites can quickly develop immunity to it. So, if you decide to use it please understand how it works and how to rotate it with another product like a horticultural oil.

So, that’s where I’m at and I hope you find this helpful. It should not scare you away from delphiniums. Just know the issues, how to handle them and you’ll love this plant just as much as I do, or more. Next week, how to grow them from seed, where to get the seeds and plant and how to take care of them in the garden. Keep growing.