Monday, May 7, 2018

Growing Swan Plant (Milkweed) for Monarchs

Monarch butterflies need milkweed for survival, and milkweed is often in short supply so things can get ugly rather quickly. The adult butterflies happily source food elsewhere from nectar-rich flowers such as your pollinator-friendly garden, but monarchs lay their eggs exclusively on milkweed and their caterpillars are milkweed dependant until metamorphosis.  In addition to nourishing the caterpillars for their weeks between hatching and pupating, the chemical compounds in milkweed sap help to make the monarch caterpillars toxic to predators.  Although many pests avoid monarch caterpillars because of the milkweed toxin, they are (in our region) vulnerable to predatory wasps.  Yes, it is nature at work, but you probably won't be happy about it. :( You can use countermeasures such as netting to protect the plants or traps to reduce wasps, but loss is part of the cycle. Our local news recently featured a hilariously written (although the subject matter itself is entirely unfunny) recount of a family's attempts at planting milkweed for monarchs, only to end up explaining a lot more about the circle of life to their kids than intended. Nature is wonderful, but it can be rather terrible, too!  

Planting milkweed can help support the local monarch population (or depending on where you live, transient monarchs).  When selecting milkweed seed or plants, a local native variety is the best option, especially if you are planting in an area where your transient monarchs should be moving on as seasons change.  In our part of the world, the swan plant is the popular species of milkweed to plant for monarchs (and other Danaus family butterflies).   Monarchs aren't native to New Zealand, but we love them all the same (here is a link to the Monarch Butterfly New Zealand Trust for fellow kiwis).  Just like the monarchs, the swan plant isn't native to New Zealand but it has been naturalised.  It is a perennial shrub, but is frost tender so often treated as an annual here. Swan plants are also known as balloonplants and the not-so-subtle bishop's balls for rather obvious reasons. Check out the seed pods! Oh my.

Swan plants prefers sandy well-drained soil and full sun, and since they can grow up to 2m tall they also benefit from wind shelter or support. Always remember that swan plants are toxic if ingested and swan plant sap can cause serious topical reactions, so take care, especially when gardening with children and pets. Wear gloves, protect your skin and eyes from sap if pruning, and wash up well after any/all handling - see the NZ National Poisons Centre for more detailed guidance.

When planting as a food source, it's essential that you purchase your plants from a reputable source (or grow your own from seed) to avoid inadvertently planting milkweed that has been pre-treated with systemic pesticides. Avoid using any pesticides on or around your swan plants in the garden as this will also harm your monarchs. Try companion planting for deterrence and/or deal with pests manually where possible. Encouraging ladybird/ladybugs and other beneficial insects to help - aphids and byproduct honeydew sooty black mold are key pest problems for swan plants around here. Protect plants from slugs and snails around the base with pet/wildlife safe countermeasures, especially during spells of cool wet weather.

Make sure your monarch milkweed buffet is well stocked!  Monarch caterpillars chew through milkweed like you wouldn't believe! Plant multiples plants in groupings. Plant multiple batches of seeds in succession every few weeks to help ensure that you have enough milkweed to sustain caterpillars through to autumn.  If space allows, you can isolate some plant groupings with protective netting so that monarchs can't reach them to lay eggs so that you can have them in reserve for later food sources when needed and/or you can net egg laid plants to curb the number of eggs to help ensure adequate food supply. If you have a lot of predators, netting some of the plants during hatching and caterpillar growth can be beneficial for reducing losses as well. Tip: In addition to in-ground planting areas, I also like having a few potted plants on hand for ease of mobility.

When planning your planting locations, look for a suitable aspect in your garden in a position where you can (if you wish) mask the milkweed with foreground plantings or position the plants discretely so that the caterpillar pillaged stems don't ruin the look of your landscaping.  Making accommodations for ugly spells in the growth/feeding cycle will help you resist the urge to ditch the dregs before regrowth and/or seed set.  If they're been thoroughly nibbled early in the season, you can prune the eaten swan plants back for another round of regrowth. Nourish nibbled and/or pruned plants with seaweed solution and/or liquid fertilisers (root feeding is best to avoid residue on the leaves) to aid regrowth.  If your plants set seed, you can allow them to self sow or save seed for replanting.

Even if you milkweed hasn't been nibbled to a stub, periodic pruning also helps reduce the spread of disease building up over multiple generations.  Pruning can also help straggly plants bush out to increase the food supply.  Tip: although seed-sowing is the usual method to propagate, I've had good success with propagation through cuttings taken during pruning. A great way to replace or increase supply for future caterpillars or to gift plats to friends and neighbours.

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