New Millennium Delphiniums (NMDs) are grown successfully as perennials in all except the hottest and most humid areas of the USA, but even there enthusiasts grow them as annuals.
Much emphasis is placed on mulching. This should be quite thick, maybe three or four inches deep or greater if very loose (like straw). The mulch helps to keep the roots moist and cool (most desirable)
People who grow delphinium successfully where summers get very hot (95degF+) all use some sort of shading to protect the plants from the worst heat of the day. This shading usually takes the form of trees which cast a shadow over the plants. The tree could be quite loose leafed. Adjacent trees help cool the ground too. If growing as annuals plant at the end of summer and flower before the heat of the following summer.
General agreement here too. Most folk water deeply every two or three days during hot weather (some even daily) and maybe once a week at other times. The key is to water deeply. I would add a cautionary couple of notes here. 1) Never let delphiniums get either bogged or dried out, particularly when growing well. 2) Keep only barely moist immediately after cutting down after the first summer flowering (July) or they may rot. Increase water as the plants grow back. Be sure the soil is moist going into a hot spell.
New Millennium Delphiniums (NMDs) are very hardy. They are grown without trouble in Alberta, temperature range –40degC to +30degC. Winter mulching benefits here and folk often use pine branches to provide a loose protection from severe frosts. We have a report of them going rampant in South East Alaska, growing to two stories high and being tended through the upper level bedroom window. This is unusual however. Incidentally, they grow magnificently throughout Russia too.
NMDs normally grow between three and six feet tall according to methods and varieties used. Those gardeners who give the plants plenty of space and water lightly restrict their height to between three and four feet. Gardeners who plant more closely together, water, feed and mulch well get taller plants.
Gardeners all agree – the more you feed them the better the plant. Animal manures seem to give the best results but people often use a general fertiliser from the local garden store. We receive regular comments about how strong stems are and how green the foliage is – much more so than Pacific Giants
The most common type of delphinium grown is "Pacific Giants" as this is the most readily available. General consensus is that New Millennium Delphiniums are far more robust and last much longer in the garden as well as giving a much better show. This is why the famous Butchart Gardens in Victoria on Vancouver Island BC, Canada and Walters Gardens, the largest wholesale specialist supplier of perennial garden plants in the USA, now grow and stock only New Millennium Delphiniums.
Probably the best reward for us, as a plant breeder, is receiving reports from people who are blown away with the results from plants that we have bred. When these reports come from gardeners, commercial growers, open to public gardens, the public generally, garden writers and critics, not just from our home country of New Zealand but from the USA, Canada, England, Russia, indeed from all over the world (except the tropical lowlands) it is especially gratifying. And they do.
From Carol Madsen C&C Nursery Vancouver Island, BC
".... Also my old customers tell me that THEIR customers come back to tell them how amazing these plants are in their 2nd and 3rd year
NM's are amazing--seriously we may have lost--less than 10 plants out of thousands."
Allan Becker Gardenguru
"I had a love-hate relationship with Delphiniums for as long as I have been gardening. I stopped growing them many years ago. That was due to never having the time to give these awesome plants the attention they deserve. Now, I am ready to reconsider, but not for using the good old favorite, Pacific Giant Hybrids, which are not good, not my favorite, just old. I wish to experiment with a new robust strain called New Millennium. Word is out that this new collection has an extended life. That is hard to believe, but it’s an incentive to try growing Delphinium, again."
And a comment to Allan's blog post:
"Allan, I've been growing New Milleneum delphinium for several years (you're looking at them in my blog header photo); I'm lucky to have a local nursery that grows them from seed. I have been very happy with them and have found them much easier and longer lasting than older varieties. In my garden, they usually bloom twice in the season. They are still delphinium, though, and some years I will just lose some of them. I will reiterate your point about feeding them; I've found I need to feed them early in the season and then again after the first blooming."
March 2, 2010
See full article here
From Master Gardener Magazine Winter 2010 –
“New Millenniums have proven to be far more robust and vigorous plants (than Pacific Giants)” – Wendy Tweten, Garden writer.
“It became clear that these palnts were excellent performers and they were vigorous and healthy and produced an abundance of long lasting blooms” – Rick Los Director of Horticulture for Butchart Gardens
From The Royal Horticultural Society Blog
Graham Rice - "Ter28-Apr-2014ng away producing superb new varieties. He's the finest delphinium breeder in the world and we saw some of his plants in last year's trial of delphiniums from seed at Wisley.
By diligent hand pollination of specifically chosen parent plants he produces a wide range of varieties in a fantastic range of colours ensuring that variations in colour and quality are eliminated so you can really depend on the results. One of his varieties was awarded an Award of Garden Merit at last year's trial and seed is now becoming easy to buy."
After a couple of years of trying, I think that I have worked out how to grow delphiniums in Virginia. I have been able to grow the seedlings (I use crushed sponge rock and ground sphagnum moss to cover the seeds and there is no problem with damping off), but I was not able to get most of the plants to grow on in the hot, humid Virginia summers.
Now I no longer plant the seeds (indoors) in the late winter for Spring planting. I start the seeds in the summer and plant them out in the garden in early Fall, to become established before going dormant in the winter. The plants are now up and growing and will bloom this Spring/early summer. I will treat them as an annual and not expect them to last through the summer. If they make it through the summer ( a few do) then it is a bonus.
Hi Janice, I sent you a letter and some pictures last year of the beautiful delphiniums I purchased from you and raised. This year, they outdid themselves and were spectacular. Some of the deep blue and purple ones reached 8 feet tall! I'll send some pictures so you can see them. My granddaughter is in one of the pictures so you can see how tall they are! Many people drive by and look at them, and some people stop and ask for a closer look. They marvel at the sheer size and brilliant color. The flower create quite a sensation. Thank you for much for making this possible!
From Susan in Seattle
"You can see how much pleasure your beautiful plants bring me and my neighbors. The health and color of these plants is incomparable to anything people can buy or grow from US seed around here."
Another Susan reports her delight in successful delphinium raising:
"Last year, I ordered seed from you, planted, and achieved flowers on some of my plants. I e-mailed you, mainly to share my pleasure. This is a follow up, and I couldn't be happier. I am the envy of the neighborhood, and if they only knew it, the rest of Pennsylvania, USA. All of my plants survived a very mild winter, not much snow cover. The lack of cold has caused me problems in the past. I did mulch well so that frost heave wouldn't be a problem. This spring I fertilized with Osmocote, once. I haven’t had a chance to get to it again. I have many white and shades of pink delphs towering over 8 feet. A lovely lavender that I transplanted in the late spring that is around 4 feet. Same with some lovely blues. The side branching on all of the plants is plentiful enough to ensure bloom for some time to come. I just cut a lot of flowers to bring in. I was unprepared for the heights of these plants, and didn't do enough staking. Live and learn. I have also had no problem with a dreaded insect or worm that has done major bud damage in the past to other delphs I've tried unsuccessfully to grow. This may just be luck. Anyway, thank you and I will continue to order seed from you. God knows where I'll plant them."
Thank you, Susan Brunell
From PA., Zone 6, USA