Freezing Milkweed Leaves for Emergency Use

What do you do when you run out of milkweed? There are several options that can save the life of a caterpillar in such an emergency situation.

Many people are able to keep feeding caterpillars milkweed, even when they don’t have any growing outside. They have planned ahead for such an emergency. Frozen common milkweed leaves work adequately for older Monarch caterpillars.  Fresh is always better but frozen can mean the difference between life and death.  Frozen milkweed provides the nutrients that they need.Please understand that frozen milkweed leaves are not the best food for caterpillars. Old tough leaves that have not been frozen are better than frozen leaves.  Frozen leaves are mushy and have a different consistency, easily torn, and messy to handle once it has thawed.

If you know you will need leaves in two weeks and are afraid that the field will be mowed or there will be a freeze, prepare some and freeze some, yes. At the same times, wash and refrigerate leaves to use. Store the washed and dried leaves in a plastic bag in the refrigerator as you would store lettuce. Use the frozen leaves only if the refrigerated leaves are not edible. Frozen leaves are almost a last resort but better than non-milkweed food. (Human food can be frozen, thawed, and eaten without problem. Caterpillar food is different. Think frozen lettuce compared to older refrigerated lettuce. In an emergency, frozen is better than nothing but older refrigerated lettuce is better than frozen.)

People who raise Monarch caterpillars indoors often run out of milkweed in the early spring. During other times of the year, emergencies arise. The county may unexpectedly spray for mosquitoes, the neighbor may spray his lawn (with over-spray coating milkweed in the wrong yard), an unexpected number of caterpillars may decimate the number of leaves available, or someone may become too helpful with the lawn mower. Whatever the cause, a milkweed emergency can mean death to dozens of caterpillars one is raising indoors.


To prepare for such a situation, you can pick nice healthy common milkweed leaves and place them in a plastic bag. Remove all the air from the bag and seal it. Place it in an ice chest or refrigerator until you are able to clean and freeze the leaves.


Old, pest eaten, aphid infested, nasty leaves should not be saved. Nice mature or nearly-mature leaves are great for this purpose. Wash the leaves, pat them dry, and layer them between paper towels.

The layers of leaves and towels should be placed in a plastic bag, labeled with the contents and date. Because the package is going into a home freezer, contents labeling is important. We don’t want them mixed up with our food and added to the family meal. Because we should be doing this twice a year, labeling the package with the date is important. We need to know which package holds the leaves that were processed LAST and use those leaves first. The leaves that were processed first should be thrown out as soon as we have enough new leaves to replace those that were processed earlier in the year or the year before.

Leaves may be used over a year after they are frozen. For best quality leaves for your caterpillars, replace every six months.

IMPORTANT! If you are gathering leaves from along a road, be aware that mosquito spray could be on the leaves and sicken or kill your caterpillars. You should freeze leaves that you are positive are not contaminated with any type of pesticide/insecticide.

We recommend that you clean and freeze leaves as soon as there are enough to spare from your garden, field, or roadside. Label your packages with the contents and date. Later in the year, before all the leaves growing outdoors are old and nasty, process and freeze more leaves. Once you have frozen enough to replace the first batch, throw out your first batch.

By processing two batches a year, you are creating extra work, yes. You are also ensuring that the leaves you thaw are not older freezer-burned leaves. They would have been in the freezer for six months or less.

For extra protection, wrap the package in aluminum foil before it is labeled. This provides an extra layer to protect the leaves against freezer-burn and dehydration.


Remove frozen leaves from the freezer and take out the number of leaves you need for your caterpillars. Carefully seal the remaining leaves and return them to the freezer before they thaw.

Place the frozen leaves into a habitat with your caterpillars. If possible, place the leaf against an object that will hold it above the bottom of the habitat or rearing container. As the leaf wilts, it may trap a caterpillar underneath it, suffocating it. A coffee cup or similar object will work well with larger leaves.

TIP FROM RICK MIKULA, butterfly expert:
“If your caterpillar’s frass turns bright green your leaves are too moist.”  Please note that a caterpillar’s frass color often depends on what it is eating.  If the leaves are nice and green, frass is usually nice and green.  “Bright green” indicates a new color, unlike a normal frass color.  Unusual frass color (not related to the color of what they are eating) can indicate problems.

In the photo below, you see colors ranging from dark green (dark green leaves) to light green (pale giant milkweed leaves) to lavender and burgundy, depending on the color of blooms they were eating.  All of these are normal frass colors when the caterpillars’ diet is considered.

frass colored .6