Milkweeds can be grown from seed, cuttings, or even root divisions in some situations. A brief discussion on milkweed seed propagation from cuttings will also be included in this account.
There are two ways to start milkweed seeds indoors: in a flat or in a prepared bed outside. Since germination rates are often higher inside and it is easier to establish your milkweeds with transplanted seedlings that are well-rooted and consequently more resistant to weather extremes and pests, we prefer the latter technique.
Growing, Transplanting, and Germinating
After the average date of the last frost, milkweed seedlings can be started indoors in a greenhouse or under artificial lighting. Prior to transplantation, germinate seeds inside for four to eight weeks. Seedlings can be started in plastic flats. Flats should be filled with an appropriate potting soil mixture and watered thoroughly so that excess water may be drained away. Seeds should be scattered on the soil surface at a distance of 1/4-1/2 inch apart, and then covered with about 1/4 inch of more soil mix. Apply a light mist of water to the soil surface to wet the newly-added soil mix. Seed packets constructed from paper towels and soaked in warm water for 24 hours are commonly used by many gardeners in an effort to increase germination rates. Seeds of species that need stratification appear to benefit most from this strategy.
A clear plastic cover or plastic bag can be used to keep the seeds from drying out as they germinate in the flats. Finally, put the flat in a greenhouse or under grow lights. If the temperature in the flats is kept at 75 °F, most seeds will germinate in 7 to 10 days. Remove the plastic covering from the flats once the seeds have germinated. Soil moisture should be maintained after seedlings have sprouted by watering the flats from the bottom. A sink or larger container with 2 inches of water can be used to water the soil from the bottom until moisture develops on the soil surface. Moisture should be maintained in the soil, but seedlings should not be overly wet, as this promotes fungal growth, which can lead to the death of immature seedlings (“damping off”). Damping-off can be reduced by thinning (see below).
When the plants reach a height of 3-6 inches, they are ready to be transferred. Place the plants in a covered spot during the day and bring them indoors at night for a few days before transplanting. Depending on the species, seedlings should be spaced anywhere from 6 inches apart to 24 inches apart (check the back of your seed packets for information). Regular watering is necessary for newly transplanted plants. The seedlings should be mulched as soon as possible after planting. As a result, the mulch acts as a barrier to keep out competing weeds. Fertilizing the seedlings 2-3 times a year with a water-soluble fertilizer or once a season with granulated time-release fertilizer is recommended for seedlings.
Thinning
It is common practice to mix small seeds with sand or fine soil before they are sowed in order to improve seed dispersal. However, thinning seedlings will still be essential, as this strategy does not totally eliminate seedling crowding. Plants get greater light and air circulation because to thinning, which creates more space between them. After germination, seedlings may need to be trimmed multiple times. You’ll wind up with weaker plants if you don’t thin out your crops.
When Should I Plant My Seeds?
After the risk of frost has passed, milkweed seeds can be sown outside. See the seed packs for specific sowing instructions. As a reminder, keep in mind that seeds can germinate in a wide variety of soil temperatures. Consider the fact that in sunny weather, soil temperatures can be substantially greater than the air temperatures you experience throughout the afternoon. The high temperatures of the season may prevent seeds planted later in the season from germinating. Late plantings, in particular, might cause young seedlings to “dry off” before anyone notices them. Swamp milkweed and common milkweed both germinate poorly at hot temperatures (>85°F). The temperatures are ideal for the germination of tropical milkweed (A. curassavica) and blue vine (Cynanchum leave). If soil moisture and temperature are not ideal, it could take several weeks for a seed to germinate outside.
Seedbed Preparation
As a first-time gardener, it is a good idea to check with your county extension agent to determine whether your soil needs to be improved before you plant the seeds.
Seed germination and seedling establishment are almost assured if the seedbed is smooth, clump-free, and free of weeds. A tiller or a hoe can be used to remove any vegetation that may be present in the area where the new habitat will be built. Avoid working the soil when it’s damp to minimize clumping. To promote optimal soil-to-seed contact, the soil should be churned down to a fine consistency.
Until the seeds germinate, make sure the seedbed is wet. It’s critical to prevent overwatering or underwatering the seedlings as they grow. Until the roots are fully established, a gentle watering once a day, preferably in the morning, should be plenty.
Milkweed Cuttings Growing
Perennial milkweeds can be propagated from cuttings. Cuttings are a quick and easy way to grow new plants without having to deal with the challenges of beginning them from seed. To begin cuttings, dip the stems in a strong rooting hormone before cutting them underwater. Keep the stems moist, whether in the sand, vermiculite, or potting soil. Six to ten weeks is the typical time frame for transplanting cuttings. Survival rates are higher when cuttings are taken from plants fertilized two weeks earlier and taken from green stems (1/3 inch diameter).
Types of Soil
In general, light soils are preferable to heavy clay ones. Swamp milkweed (A. incarnate) and A. sullivantii, for example, perform well in waterlogged soils, despite the overall preference for well-drained soils.
Choosing a Location
In order to thrive, milkweed should be placed in the sunniest parts of your garden where it may get plenty of direct sunshine. The partial shade appears to be required by some species, such as A. purpurascens.
Obtaining and preserving Milkweed Seeds
It is vital to collect milkweed pods or seeds at the right time of year. Pods that are close to opening are considered mature. If the pods don’t open easily when you squeeze them, they’re probably not full of mature brown seeds. They will germinate the following year if they are mature enough to do so. Seeds that are light in colors, such as white or ivory, should not be gathered. A well-ventilated place is ideal for drying freshly harvested pods. By hand, the seeds can be extracted from the coma, or silk-like inflating substance, once the pods have dried out completely. Alternatively, the seeds and coma can be removed from the pods and placed in a paper bag. Cut a small hole at the bottom of the bag and shake out the seeds after rapidly shaking the contents to separate the seeds from the debris. The refrigerator is a good place to keep dried seeds because it is cool, dry, and free of mice and insects.
Stratification
It’s a fancy way of explaining that seeds of most temperate plants need to be stratified, which means that they need cold treatment. You can stratify seeds by placing them for several weeks or months in cold, damp potting soil (preferably sterilized), in a dark environment. The seeds can be stored in a plastic bag between damp paper towels instead of potting soil, which is more common. One reason this method is effective is that fewer pathogens are present to harm the seeds. Seeds can be planted after a stratification period of three to six weeks in soil that is 70 degrees Fahrenheit and wet. Seed germination rates are typically low when stratification is not used. Asclepias curassavica (and other tropical milkweed species) seeds don’t need to be treated in this way. A method of “shocking” seeds that have been in the refrigerator for 24 hours by immersing them in warm water appears to increase germination rates.
Astonishing Temperatures
You can use cold treatment to boost germination rates of milkweed seeds, but if you’re short on time, heat shock is an alternative (albeit less accurate) option. Using hot (120-130F) tap water, soak the seeds for 12 hours before draining and repeating three (3) times. For 24 hours, place the seeds in a plastic bag with a moist paper towel inside.
Scarification
There are several plant species whose seeds will not germinate, even after stratification. In these instances, it appears that seed coatings must be broken down or abraded using physical or chemical means. Some sort of physical abrasions, such as planting seeds in a container of coarse sand, and shaking it vigorously for 30 seconds, is usually all that is needed to “scarify.” Some milkweeds (e.g., A. viridiflora and A. latifolia) may necessitate scarification, while scarification may boost the germination rates of other species.
Perennial milkweeds can be propagated from cuttings. Native milkweed cuttings are best taken in the summer because of several convincing reasons:
- The stems of native milkweed plants are still alive and herbaceous.
- In time for fall planting, mid-summer cuttings will have established roots.
- Indoor or outdoor storage is permitted for containerized clippings.
Cuttings are a quick and easy way to grow new plants without having to deal with the challenges of beginning them from seed. Six to ten weeks is the typical time frame for transplanting cuttings. When cuttings are taken from green stems with a diameter of one-third of an inch, the plants are more likely to survive.
Native Milkweed Cuttings: How to Do It
- Equipment and set for milkweed cuttings In pots, go with organic peat or all-purpose potting soil. Cuttings can be placed in 2-liter soda bottles to create a mini-greenhouse for each cutting to thrive in.
- Adding perlite or gritty sand can help the freshly formed roots get more air.
- The soil should be adequately hydrated.
- Make holes for cuts with a chopstick or pencil inserted into the soil.
- Take cuttings and cut the stems underwater with a sharp hand pruner.
- Take a cutting with 3 to 5 leaf nodes (or a length of roughly 4 inches).
- Remove all except the top two sets of leaves from your cuttings to prevent water from evaporating through the foliage.
- Using a sharp knife, remove the bottom third of the cutting.
- Take rooting hormone and coat the base of the stem.
- Make holes in the ground and bury the cuttings.
- Cuts should be stored in a spot with some light, but no direct sunlight.
- Soak the soil and the leaves every day.
Cut-and-Pick Soil
This is a more conventional method of initiating stem cuttings than starting them in the soil. Perlite and peat moss make up an 80/20 combination. Milkweed cuttings may be more successful if you mix in sand or vermiculite. Alternatively, you can use rooting hormone powder to directly plant your cuttings in standard garden soil.
