Delphiniums, The Garden Aristocrats

This week is the last installment on delphiniums. Actually I could go on for several more weeks, but then I’d miss my 2016 new plant and catalog reviews, which I’m itching to get into. So here’s the lowdown on starting delphiniums from seed, where to buy the plants, how to maintain them and some sources for seeds and plants.There are two “ideal” times to sow delphinium seeds—now, and again in late summer. Seeds started indoors now may try to bloom late in this growing year, but I’d suggest not letting them flower. During the first year all the plant’s energies should be concentrated on root and vegetative growth and not the stress that’s related to seed production and flowering. Seeds sown in early August will result in small plants that can go into the garden or holding area in late September and will overwinter, then flower the following season.

Delphinium seeds are large enough to be easily handled with two fingers (pinching), so they are easy to plant into pots, cells or to scatter in a flat. The seeds need to be fresh and not more than a year old, and if you decide to save your seed from one year to the next keep them refrigerated in an airtight container.

When you’re ready to sow, and out here that should be from February through mid-March, first soak the seed in room-temperature water for a few hours, as this may increase germination by as much as 30 percent. Don’t allow the seed to completely dry after soaking, but they can be gently patted dry so they are easy to handle. Use a high-quality seed germinating mix to a depth of at least 2 or 3 inches. Each pot or cell should have two to three seeds on top of the soil, then cover it with about an eighth of an inch of cover soil. Make sure the soil is pre-moistened but not wet. Seeds will germinate with the soil temperature an ideal 65 degrees at night, and 75 during the day. Heat mats can be helpful but are not mandatory. A hint here is that a 2-inch-deep seed tray about 12 inches square will allow 100 to 150 seedlings to germinate with adequate space.

Keep the soil moist, but not wet, and don’t let it dry out. Germination should take 10 days or more and if you see too many seedlings emerging, thin them out with tweezers so each plant has at laest an inch of growing space. Once the seedlings have their first set of true leaves you can use a small tool or tongue depressor to tease them out of the soil. They then get moved on to 3- to 4-inch pots with one seedling per pot.

Fill the pot with a premium potting soil that has NO fertilizer in it. The soil should be pre-moistened and the pot filled to near the rim with no packing down. Use a dibble or pencil to make a hole at least 2 inches deep and drop the roots down into the hole and gently firm the soil around the plant. Never plant deeper than the seedling was when it germinated. Water lightly and keep in a bright window or under grow lights.

In two weeks you can begin to add an organic liquid fertilizer to your water and continue weekly until the next transplanting. In late April the plants can go outdoors, but keep them free from frost. They can be planted directly into the garden or in a holding area while they mature, then get moved into their final planting spots next year or at the end of the summer.

Fertilize these plants regularly with a balanced organic plant food and watch out for slugs, then later on, mites. Each plant should get a 3-foot stake next to it to prevent the main stem from snapping in strong winds. Allow the plant to grow through the growing season, and if you see signs of flower spikes developing pinch them off. It’s hard to do after all this effort but you’ll have a much stronger plant next year.

In late August or September you can transplant to the final garden location—but no more feeding after September, and if they again try to flower, pinch out the flower stem before it develops. There is no special winter care, but a very light mulch of salt hay in December will protect the plant from the freezing and thawing cycle that can lead to rotted crowns in the spring. The final planting location should have a rich but well drained soil with added compost.

Mail order plants should follow the same routine of setting them in a holding area for the first growing season then transplanting into the garden late in the season. Plants purchased at garden centers that are in 2-quart and larger pots can be planted directly into the garden and 1-gallon and larger plants can be allowed to flower, but again, discourage the second late-season flowers the first year. Inspect for mites weekly and keep slugs under control. You should expect two to three years or more from the Pacific Giants and the New Millenniums, while the shorter Magic Fountains may only go for two years.

Delphiniums like a rich but well drained soil, so for us that means our sandy soil with lots of compost. They also tend to be heavy feeders. When 1-gallon and larger plants are installed you can include a time release product like Osmocote at the time of planting. You can also use an organic liquid product with a ratio of 1-2-1 (2-4-2, 3-6-3, etc.) and dilute it so you can make weekly applications from May through September. Staking is critical and the stakes should be installed at planting time and swapped out as the plant gets taller. Tie the center stem using a soft tie and a figure 8 tying method to give support but allow some movement of the stem.

As for sources: You can get Blackmore & Langdon’s seed directly from them at www.blackmore-langdon.com, but the only way you can get B&L plants is through the White Flower Farm online, and their supply is very limited. For the New Millennium delphiniums you can order seed directly from the nursery in New Zealand at www.delphinium.co.nz. But here again you cannot buy plants from them directly (but you can buy their nursery … hint, hint). You can, however, buy the New Millenniums and their other lines through a number of U.S. suppliers, including Bluestone Perennials and gracefulgardens.com. I haven’t dealt with Graceful Gardens (yet), but they offer a full line of Pacific Giants and some of the Dowdeswell’s (New Millenniums) offerings. As they’re up in the Finger Lakes, it might make a nice drive and being that close means less shipping time.

Retail garden centers in the area may also be able to get you some of the New Millenniums, but let them know early what you’re looking for, because they don’t last once they are put out. You may also be lucky enough to find some of the new Dutch delphiniums that are being grown from tissue culture. If you’re very lucky you may find these locally as the named varieties Red Caroline, Princess Caroline and Delft Blue, but these are not the tall elatum types and while hardy they are much smaller.

So, I hope you’re tempted and I hope you’ll try some of these garden aristocrats. If you’re timid, go for the Magic Fountain series, but if you’re a risk taker and a bit more patient, go for the Pacific Giants and New Millenniums. Let me know how you do and of course … keep growing.