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Setting up a wildlife garden

Plants for butterflies

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Asclepias sp. (Milkweeds)
Milkweed with swallowtails

Zone: 3 to 8

Soil: sand to clay - see notes

Light: Full sun to part sun

Bloom colour: White, purple or orange

Bloom period: June-August

Height: 2 to 5 feet

Moisture:Dry or moist - see notes

Attracts: Many butterflies and bees.

Notes: Milkweeds are fascinating plants that are well known for being a host plant for Monarchs. There are actually quite a few insects that specifically use these plants for food. There are also many butterflies and bees for which milkweeds are a major nectar source. These plants produce a milky sap that may contain significant concentrations of cardiac glycosides. The Monarch butterfly ingests these chemicals and consequently becomes toxic as well. All stages of the Monarch's life cycle are toxic including the eggs and this is rather unusual. When a Monarch is eaten by a bird, the bird throws up and is put out of action for a while when it could be building up fat supplies for its migration or to survive the winter. The long-term decline of the Monarch butterfly populations east of the rockies is thought to be connected to the declining milkweed population in the mid-western United States. Additional milkweed in Canada and stronger enforcement of logging in the overwintering areas in Mexico would also certainly help.

The individual flowers look different to a regular flower because the stamens are fused together to form the central part of the flower. Around this, you can see five cup-like structures that are called hoods. Insects have to reach into the hoods to get access to the nectar and in so doing, they may place their feet onto the reproductive parts and effect pollination. While most plants produce individual pollen grains that attach to the insect, milkweeds produce a pair of pollinia, which are sacs containing the pollen. The pairs of pollinia are often visible on a pollinator's leg.

Most species are great wildlife plants attracting a range of bees and beneficial wasps. In general, they are slow to emerge after the winter and could well be the last plant you see starting to grow in your garden. They grow quickly and typically flower in the early part of the summer. Milkweed reseed quite easily; just pat the seeds into the ground in the fall. All the species that I have grown require some sunshine in order to start growing. Do not plant any in total shade.

The members of this genus are often subject to attack by Milkweed Aphids. You can clean them off or if you are more patient, then you can wait for ladybird and hoverfly larvae to clean them off for you. This latter option is better for ecological reasons and the plants will still do fairly well.

The most commonly seen member of this species in open areas is Asclepias syriaca. This is the common milkweed that you see growing in fields. It is not really suitable for gardens because it has a rhizomatous root system that allows it to outcompete other plants. What may look like a bunch of separate plants growing together is more than likely to be a single individual. If you have a larger garden and can dedicate some space to these plants combined with some grasses like Little Bluestem, then you will get to enjoy all the wildlife that these plants attract.

In confined gardens with plenty of sun, you could try Purple Milkweed in dry sandy soils or Sullivant's Milkweed in mesic/dry clay soils. Purple milkweed grows to about 3 ft high and is one of the most fragrant milkweeds in Ontario. It takes three years to flower from seed and three weeks to finish blooming, so be patient. In Ontario, it is a rare plant.

For dry sandy soils, grow Asclepias tuberosa - butterfly weed. It develops a long taproot that helps it survive drought, but this also makes it difficult (but not impossible) to transplant. Do not be fooled by the name. The other species of milkweed mentioned here are just as effective at attracting butterflies. Butterflyweed is commonly available in nurseries. If you do not see it on sale, try asking for a common cultivar called Hello Yellow. It makes a lovely flower combination with regular orange butterfly weed. This species makes a good companion plant in front of purple milkweed. The unusually strong colour of this flower and the coverage of the bloom makes this one of the most striking plants available, but it will not look its best if grown in clay.

Swamp milkweed (Asclepias incarnata) is a fantastic plant for either informal or formal gardens. Its profuse pink flowers come out in mid-June before many others appear and remain for a good six weeks. Their stems are strong and their leaves are ornamental in looks. These plants are covered in bees and beneficial wasps; they deserve to be planted a lot more often. This plant grows to around 48 inches whereas Asclepias tuberosa is typically two feet in height. This species grows well in ordinary garden soil or clay and tolerates some drought despite its name. If you only have room for one species of milkweed, then choose this one. It is also the most popular species of milkweed in my garden for Monarch butterflies that are laying eggs.

Whorled milkweed is sometimes available. It is a little less showy than other species and seems to attract less wildlife. However, its fine leaves and smaller stature makes it a nice addition to a wildlife garden. It flowers a little later than other milkweeds in August. It does well in dry sandy soil and is best grown en masse. It grows about 2 feet high.

In Canada, Bloodroot (or Tropical Milkweed) can be grown as an annual that is about 3 - 4 feet high. It will grow in average garden soil with a decent amount of sunshine. The flowers are notable because of the red/yellow bicolouration. This is not a plant that should be grown anywhere in the southern US as research has shown that the plant becomes a vector of parasites that affect migrating Monarchs if it can overwinter.

The Canadian species include:

Asclepias exaltata - Poke milkweed

Asclepias incarnata - Swamp milkweed

Asclepias ovalifolia - Dwarf milkweed

Asclepias purpurascens - Purple milkweed

Asclepias speciosa* - Showy milkweed

Asclepias sullivantii - Prairie milkweed

Asclepias syriaca - Common milkweed

Asclepias tuberosa - Butterfly milkweed

Asclepias varigata - White milkweed

Asclepias verticillata - Whorled milkweed

Asclepias viridiflora - Green milkweed

Milkweeds attract a range of insects
Milkweed with  Monarch butterfly
Butterfly weed with monarch
Monarch butterfly caterpillar
Monarch butterfly caterpillar on butterfly weed.
Milkweed flower structure
5 hoods surround the central part of the flower
Mason bee with pollinia attached
Many pairs of orange pollinia have become hooked onto this grass-carrying wasp's legs. They are irritating and wasps may try to remove them.
Milkweed aphids
Yellow milkweed aphids are common and can be tolerated quite well. Predators will usually control these aphids before the plant suffers any significant damage.
common milkweed
Asclepias syriaca - Common milkweed
Purple milkweed
Asclepias purpurascens has flowers with a saturated purple colour. It blooms for three weeks.
Swamp milkweed
Asclepias incarnata - Swamp milkweed
Milkweed attracts many bees
Swamp milkweed with a leafcutter bee
Whorled milkweed
Asclepias verticillata
Asclepias verticillata foliage
Foliage of Asclepias verticillata
Asclepias curassavica
Asclepias curassavica
Large milkweed bugs Milkweed beetle
Red Milkweed beetles eat the leaves of these plants. Some of these beetles are specific to a single species of milkweed.
Milkweed tussock moth caterpillars
Large Milkweed Bugs eat the seeds of these plants.. Milkweed tussock moths have aposematic colouration and the hairs make it more difficult to eat either by increasing the bulkiness or by being irritating.
Butterfly weed
A stunning patch of butterfly milkweed