It’s garden planning time. If planning a flower garden to attract monarch butterflies, there’s interesting research from the University of Kentucky about placement of milkweed in gardens.
The research, conducted by Adam Baker and Daniel Potter of UK, shows monarchs are much more likely to find and lay eggs on milkweed planted just outside the main flower garden, than if intermixed with nectar or non-larvae host flowers.
Of 22 gardens, nine were structured (designed) with milkweeds planted in a relatively uniform pattern, set off by mulch, and separated from nearby plants by about two feet. Thirteen gardens were non-structured with milkweeds intermixed amongst other plants.
At twice-monthly visits to each garden, total numbers of monarch eggs and larvae observed were about five-fold higher in structured gardens than non-structured gardens.
If aiding monarch butterflies by providing larval host plants is a main goal, increase their numbers and use of milkweeds by placing these plants on the perimeter of the garden rather than intermixed throughout.
Milkweeds commonly planted in gardens are butterfly, swamp and common milkweed. The genus of milkweed is Asclepias. The common name comes from the fact the plants have milky-white sap.
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The most common and best behaved milkweed for home gardens is butterfly milkweed (Asclepias tuberosa). Butterfly milkweed is native to Nebraska. It grows about two feet tall and blooms with orange flowers from June to September. There are yellow flowered cultivars such as ‘Hello Yellow’.
Butterfly milkweed is easy to grow, requires little maintenance and has few pest issues. They will attract milkweed bugs, who resemble boxelder bugs, but these do not harm the plants, monarch eggs or larvae. They only feed on milkweed seed pods.
Butterfly milkweed has a deep taproot so once established, it is heat and drought tolerant. Because of the taproot, it does not transplant well. If found in the wild, do not attempt to move these. It is best to buy new plants as transplanting is rarely successful.
Swamp milkweed (Asclepias incarnata) is also native. Some now call it rose or prairie milkweed since the name swamp is not too appealing. But this is an ornamental plant worth planting for its rosy-pink flowers and ability to attract monarchs.
It came by the name swamp milkweed because it tolerates wet soils. It is often planted in the bottoms of rain gardens now being established in landscapes to reduce stormwater runoff and conserve water. It also has a deep taproot and will not transplant well.
Swamp milkweed grows 3-4 feet tall and blooms from July through August. While swamp milkweed tolerates brief dry periods, it performs best with consistently moist soil. Improved cultivars include ‘Cinderella’, ‘Ice Ballet’ (white flowers) and ‘Soulmate’. It can attract oleander aphids which can be an issue.
Common milkweed (Asclepias syriaca) is mostly available for planting by seed. Also native, it tends to be vigorous and somewhat weedy as it is an aggressive, suckering perennial. If this is okay with you and for the site you are planting into, common milkweed is a great plant for attracting monarch butterflies.