Plant division and propagation

I am wondering if the following plants can be divided or propagated successfully: Heuchera, Donkey Tail Spurge (Euphorbia), Corsican Hellebore, and Helianthemum.

I consulted The American Horticultural Society Plant Propagation book,
edited by Alan Toogood (DK Publishing, 1999), and it says the following:

Heuchera: by division or by seed in spring. Since cultivars may not
come true from seed, I would recommend dividing your plants. Once spring
growth has begun, lift the plant from the ground and remove small
sections from around the edge (look for good roots, and 2-3 shoots).
Euphorbia myrsinites: (Just a note: based on the USDA information that
this plant is invasive in Oregon and banned in Colorado, I would think twice before propagating it. This species does a fine job of propagating itself, apparently. In general, the genus Euphorbia can be propagated by division in early
spring, or from spring to summer, by seeds in fall or spring, and by cuttings in summer or fall, but if you were to propagate by cuttings, you would need to protect your skin from the sap.
Helleborus argutifolius can be propagated by division after flowering,
or by seeds in summer. Test seed capsules for readiness by gently
squeezing. If the seed capsule splits to reveal dark seeds, it is ready
for harvest. Wear gloves! H. argutifolius (Corsican hellebore) often
self-seeds. Check around the base of the plant in spring. When each
seedling has at least one true leaf, gently lift and transplant to moist,
fertile soil in light shade.
Helianthemum can be started from greenwood cuttings rooted in summer
and fall, and by seeds sown in spring in a frost-free location.

If you would like further information on the relative ease or difficulty
of each of these methods for each of these plants, I recommend coming to
the Miller Library and looking at our books and other resources on
propagation. Here is a link to a booklist.

Euphorbia, Helianthemum, Helleborus, Heuchera, Invasive plants, Propagation

resetting and dividing Heucheras

Why does my Heuchera lift out of the ground while growing? Should I replant it back down into the soil? If so, when and how do I do this?

I have observed this in my own garden and wondered why those heucheras keep heaving themselves out of the soil. According to Heucheras and Heucherellas by Dan Heims and Grahame Ware (Timber Press, 2005), most heucheras “require resetting or mounding every two years. A heuchera is in need of such a treatment when its rhizomes’ stems exceed three inches in length. […] Remove stem tips with a sharp knife or razor and plunge them into the ground or into potting soil to make more plants; lateral buds will emerge the following spring. Resetting a plant involves ‘popping’ the rootball out of the ground, digging a deeper hole in the same spot or elsewhere, and resetting the plant with 3 inches of soil mulch. It is important not to cover the crown tips, as this may cause rot or death. Some people think it is easier simply to mound 3 inches of mulch over the plant, but we prefer resetting–which is also a good opportunity for dividing the plant.[…] Early spring, when the ground thaws, is our preferred time for this operation. Without this treatment, many heucheras show less vigor, less flowers, and less foliage.”

on managing weevils in the garden

What is the pest that eats little notches around my Bergenia
and Heuchera? What can I do to prevent this?

It is possible your Bergenia and Heuchera are being nibbled by black vine
weevils or strawberry root weevils. Usually you would begin to notice the
damage in mid-spring. The notches won’t kill your plants, but if you have
a lot of black vine weevils and plants appear to be wilting, you may want
to attempt to control the larvae. Spraying beneficial nematodes
(Steinernema) on the surrounding soil may also help.

Below are links to information about weevils:

Black Vine Weevil from UMass Extension

Black Vine Weevils from University of California’s Integrated Pest Management site

Strawberry Root Weevil from the Pacific Northwest Insect Management Handbook

A document about Black Vine Weevil (and other root weevils) from Ohio State University Extension

Excerpt:

“Adults that feed along leaf margins produce typical crescent shaped
notches. Careful searches should be made to try and locate specimens
since several other weevils and some caterpillars can produce this same
type of notching. Moderate to light notching seems to have little effect
on plant health.

“Black vine weevils are oblong oval in shape, about 1/2-inch long and have
a short, broad snout with elbowed antennae. The body is slate grey to
blackish brown and the wing covers have numerous small pits and short
hairs. This pest is difficult to distinguish from other Otiorhynchus
weevils. The strawberry root weevil is usually half the size of the black
vine weevil, and more brown in color. The rough strawberry root weevil is
only slightly smaller than the black vine weevil but the collar just
behind the head, the pronotum, is heavily pitted.

“Female weevils emerge from soil pupation chambers late May to early July.
These weevils must feed on plant material for 21 to 45 days before they
are ready to lay eggs. After the preoviposition period has passed, the
females place several eggs each day into the soil or leaf litter nearby
suitable host plants. The weevils hide during the daytime at the base of
plants or in mulch and leaf litter near food plants. Adults may live 90
to 100 days and usually lay 200 eggs during this time. The eggs hatch in
two to three weeks and the small C-shaped, legless larvae feed on plant
rootlets. The larvae grow slowly over the summer, molting five to six
times. By late fall the larvae have matured and are about 5/8-inch long.
The mature larvae enter a quiescent prepupal stage in an earthen cell and
pupate the following spring. A single generation occurs each year.

“Strategy 1: Habitat Modification – Egg and larval survival is helped when
soil moisture is moderate to high in July and August. Heavy mulches also
help maintain critical moisture levels. Remove excessive mulch layers and
do not water plants unless necessary. Excessively damp soils in the fall
also force larvae to move up the base of the plant where girdling can
occur. Properly maintain rain down spouts and provide for adequate
drainage of soil around plants.

“Strategy 2: Biological Control Using Parasitic Nematodes – The
entomopathogenic nematodes, Steinernema and Heterorhabditis spp., have
been effective for controlling black vine weevil larvae, especially in
potted plants. Sufficient water must be used during application to wash
the infective nematodes into the soil and root zone. If the nematodes are
to be used in landscape plantings, remove a much of the mulch as possible
and thoroughly wet the remaining thatch and soil before and after the
nematode application. Applications of the nematodes in landscapes has
produced variable results.”