Gadenin日本語Get the appBasal cuttings: the method that gives you the same plant
Spring thinning and propagation are the same operation. When you reduce a clump from a dozen shoots to five or six, the shoots you remove are the cutting material, and they root more readily than almost anything else in the border. This is the standard way to increase a delphinium, and it is the only method that gives you a plant identical to the one you took it from.
Take them when the shoots are three to four inches (8-10 cm) tall and still solid right through. That last point is the whole trick: a delphinium stem becomes hollow as it lengthens, and a hollow cutting rots off at the base instead of rooting. Snap a shoot and look at the cut end. If you can see a pith cavity, it is too late for that shoot.
Scrape the soil away from the base of the shoot and take it off with a sliver of the woody crown attached, using a sharp knife rather than pulling. That small heel of firm tissue is where the roots come from and a cutting taken without it is much less reliable. Firm the soil back around the parent crown afterwards.
Expect roots in three to five weeks in a cool bright place. Kept growing on through the summer, a cutting taken in spring makes a plant strong enough to go into the border in autumn and to flower properly the following season.
- Choose solid shoots three to four inches (8-10 cm) tall Take the fat, short, firm ones. Anything taller than about four inches (10 cm) is likely to be hollow at the base already and will rot rather than root. Wear gloves; the sap is an irritant.
- Cut with a heel of the crown Draw the soil back, slide a sharp knife down beside the shoot and cut so a thin sliver of the firm crown comes away attached. Trim any ragged edge cleanly with the knife.
- Trim and insert Remove the lowest leaves so no foliage will sit on the compost, then push the cutting an inch to an inch and a half (2.5-4 cm) into a pot of gritty, free-draining cuttings compost. Two or three to a four-inch (10 cm) pot is fine.
- Keep cool, bright and barely moist Stand the pot somewhere bright, out of direct midday sun, at around 60F (15C). Cover loosely to hold humidity but ventilate daily. Wet compost is what loses delphinium cuttings; damp is enough.
- Pot up once rooted In three to five weeks resistance to a gentle tug means roots. Move each one to its own pot of ordinary potting mix, grow it on outdoors through summer, and plant it in autumn.
Dividing a congested clump
Division is the job for a clump four or five years old that has gone woody in the middle. The symptom is a plant that throws up plenty of shoots but cannot support any of them, with the vigor visibly concentrated in a ring around the outside and a dead or feeble center. Splitting it restores the plant and gives you several more.
Do it in spring as growth is starting, when you can see where the live buds are and the plant is going into a period of active growth rather than sitting wet all winter. Lift the whole clump with a fork, working well outside the root spread, and wash or shake enough soil off the crown to see what you are cutting.
Cut the crown apart with a knife, not by tearing. Each division needs at least two or three healthy buds and a decent share of the fleshy roots below them. Throw the woody center away; it has nothing left to give. Aim for pieces about the size of a fist rather than the smallest viable fragments, because small divisions take an extra year to catch up.
Replant immediately at the same depth the clump was growing, with the buds at soil level, firm the soil and water in. Then remove the flower buds from a division in its first summer. It cannot build roots, crown and a spike at once, and letting it flower is why so many divisions sulk for two years afterwards.
Seed: plenty of plants, but not the plant you had
Delphiniums set seed freely and it germinates well, so raising them from seed is easy and cheap. What it will not do is reproduce the plant you collected from. Seedlings from a garden clump vary in height, in spike density and above all in color, and the range includes plenty that are noticeably poorer than the parent. If you want more of a particular plant, take cuttings; if you want a lot of delphiniums and are happy with variation, sow seed.
Freshness matters more with delphinium than with most perennials. Seed loses viability quickly at room temperature, so sow it as soon as it is ripe or keep it cold and dry until you do. Old seed from a warm drawer germinates thinly and unevenly, and that is usually the explanation when a sowing fails.
The seed itself is among the most poisonous parts of the plant. Keep packets labeled and out of reach, and wash your hands after handling. The full detail on temperature, depth and getting a seedling through to flowering size is on the sowing page.
One practical use for seedlings even when you do not want variation: grow a batch on, flower them, then take basal cuttings in spring from the one or two you actually like. That turns a random batch into a stock of a plant you chose.
| Method | When to do it | Comes true? | Time to a flowering plant |
|---|---|---|---|
| Basal cuttings | Spring, shoots three to four inches (8-10 cm) and solid | Yes, identical to the parent | Flowers properly in its second season |
| Division | Spring, as growth starts | Yes, identical to the parent | Flowers the season after division; disbud in year one |
| Seed | As soon as ripe, or from cold-stored seed | No. Height, density and color all vary | First modest spikes in the second year |
Aftercare, and what to write down
The commonest way to lose a rooted cutting or a fresh division is to overwater it. A delphinium root is fleshy and it rots in cold wet compost, so keep young plants just damp, in a free-draining mix, and stand them where air moves around the pots. Cuttings under a cover need ventilating every day or the foliage molds.
Slugs treat a young delphinium in a pot exactly the way they treat the spring shoots in the border. Stand pots up off the ground on a bench, keep the area around them clear, and check them at night in mild damp weather. Losing a rooted cutting to a slug in late summer, after four months of care, is a needless way to end the exercise.
Plant out in autumn into ground that does not lie wet in winter, spacing plants eighteen inches to two feet (45-60 cm) apart so air moves between the clumps once they are grown. Set the crown at soil level, not below it, and mulch the root area while keeping the mulch clear of the crown itself.
Keep a written note of which parent clump each cutting or division came from, the date you took it, and where it went in the border. Delphinium seedlings and cuttings look identical for their first year, and by the time they flower and you can tell them apart, memory has failed. A row of labels and a line in a notebook is the difference between deliberately building up a plant you like and ending up with an anonymous mixture.
Wear gloves for every stage of propagation. Every part of a delphinium is poisonous if eaten and the seed most of all, while the sap irritates some people's skin. Keep cuttings, divisions and seed packets away from children, pets and anywhere livestock graze.