What to do with Native Seedlings after Winter Sowing

So, you’ve sown native plant seeds, but you aren’t sure what to do next. Follow along with this guide to learn how to care for your plants before moving them out to your garden! Planting native plant seeds either outdoors or indoors in winter is a great way to get a head start on the growing season and grow stunning plants to add to your native wildflower garden. But after sowing seeds over the winter to grow plants like milkweed, columbine and turtlehead, how exactly do you maintain your plants until they’re ready for transplanting? In the guide below, we’ll walk you through everything you need to know to maintain wildflower seedlings indoors until they’re ready to be planted in your garden in spring!

Starting Seeds Outdoors

Most native plant seeds can be started in pots or milk jugs (click here for more information about this method) and put outdoors for the duration. If you use the outdoor method, the fluctuations of winter temperatures will condition—or stratify—the seeds, letting Mother Nature take charge. Make sure your pots are in a place where they can get rain (and snow), are out of the full sun, and are protected from rodents with window screening or hardware cloth if not sown in the jugs. Start checking on your seedlings at the end of April or beginning of May. If you are using milk jugs, you may want to open them up when temperatures hit the mid 50s so they don’t get too hot when they get some sun, but close them at night to protect from frost and keep moisture in. Once you see signs of germination you will need to be more vigilant about watering when rain is lacking.

Caring for Wildflower Seedlings Indoors

(appropriate for seeds that do not need conditioning, such as swamp milkweed)

After sowing, you’ll need to provide regular water and bright light to encourage germination. Some seeds may also germinate better with the addition of a heat mat. You can use a humidity dome to help seeds sprout faster, but this should be removed after germination occurs. Then follow the steps below to support wildflower seeds while they grow indoors.

Light

After sowing wildflower seeds, it’s important to provide them with plenty of bright light to prevent leggy growth. Legginess is a common problem with plants started inside and it can result in plants with weak stems and poor growth...and you definitely don’t want that! If you added a grow light to your planting setup and have it on a timer to provide 18 hours per day, you’re probably providing enough light to seedlings to prevent legginess, but you may need to adjust the height of your grow light as seedlings develop. Grow lights should be about 2 to 4” above your plants at all times, but fast-growing seedlings can rapidly become too tall for lights. That’s why many grow lights are hung on chains, which can be easily raised to accommodate taller seedlings. If you notice seedlings are beginning to get leggy, you’ll want to act quickly and move your seedlings closer to a light source. When legginess is caught early, it is often reversible!

Water

Beyond light, seedlings will need regular watering to grow properly. While you can water seedlings with different methods, bottom watering is usually the best choice, since it’s less likely to result in overwatering. To bottom water seedlings, add about 1” of water to a seedling tray and then place seedling pots into the tray and let them sit in the water for about 15 to 20 minutes. After this time, remove the plant pots from the water and allow the pots to drip dry before returning them to your grow room or seedling setup. This allows seedlings to absorb the amount of water that they need and keeps seeds from sitting in too much water, which can result in root rot. Bottom watering also allows you to easily apply fertilizer to seedlings. Simply add the diluted liquid fertilizer of your choice to the seedling tray when watering and let your plants do the rest!

Fertilizer

Seeds contain nutrients that support the initial growth of seedlings, so it’s not necessary to add any extra fertilizer when planting wildflower seeds. However, after sprouting, plants can benefit from additional fertilizer to keep them growing strong and to prevent any potential nutrient deficiencies. If you used a seed starting mix with added fertilizer, you may not need to fertilize your seedlings while they’re growing indoors. But if you used a standard seed starting mix, fertilizer can be a good idea. However, you’ll want to wait until seedlings are about 3” tall and have several sets of “true leaves” before adding any fertilizer. When you’re ready to fertilize seedlings, opt for natural products, like kelp meal or fish emulsion, and select liquid fertilizers, which are easier for seedlings to absorb. To apply, simply dilute the fertilizer to the recommended strength and then apply it once a week or so as part of your regular watering regimen.

Air flow

Since you need to water plants often as they develop, grow rooms can be quite humid places. But, when high humidity is combined with poor air flow, it can result in plant diseases, particularly damping off. This disease is caused by fungi that thrive in humid areas, and it can cause wildflower seedlings to wither and die en masse. To avoid issues with damping off, you may want to add a small fan to your grow room. The fan will increase air flow around your plants and the added movement from the fan will encourage seedlings to develop thicker and sturdier stems.

Thinning Out and Repotting Wildflower Seedlings

When wildflower seeds are a few inches tall and have several sets of true leaves, it’s time to think about transplanting into larger containers or into the garden. Unlike vegetable seedlings, native plants do not mind being crowded, so this is not as critical as with your garden plants. When you are ready and your seedlings have thickened stems and full-sized leaves, you can either gently tease seeds apart and repot them individually or you can snip off the weaker seedlings with scissors and just keep the seedlings with the strongest stems and best growth. Both of these tactics will work; however, you’ll need to be very gentle if you’re separating seedlings because their stems are very tender and break easily. Cutting off weak plants and just keeping the strongest seedlings can be a safer method since you won’t be disturbing the plants’ roots and you won’t accidentally break any seedlings stems with rough handling. Sometimes just breaking apart the root ball with several seedlings together is the easiest way to repot or plant out in the garden. Small clumps of the same species happen all the time in nature and do just fine.

Signs that you should repot your native plant seedlings include:

Plant roots are visible or coming out of the bottom of their pots.
Seedlings are at least twice the height of the pot they’re growing in.

Repotting will allow plants more soil space to develop healthier root systems, and it will also eliminate the chance that plants may develop deficiencies due to overcrowding. This is a great way to grow healthier plants and prepare them for eventually being transplanted into the garden.

Pots that are 3 to 4 inches in diameter are usually a good choice for repotting as they will give most plants enough room to grow until they’re ready for the garden.

Transplanting Wildflower Seedlings

After caring for plants while they are small, you can finally move your plants out into your garden. But hold that thought for a second! Wildflower and native plant seedlings that are started indoors are accustomed to a certain amount of light, water and a particular temperature. If you move plants outdoors too quickly or too early in spring, they may succumb to transplant shock, which can damage or kill them. To avoid this, you will need to harden off any seedlings started indoors to help them transition to life in the garden. Likewise, plants that you started outdoors will need to become accustomed to full sun if that is their intended location in the garden.

You should begin to transition your native plants to the garden after all danger of a hard frost has passed. In Maine, this is usually early to mid-May, but many will not be ready that soon. To acclimate seedlings raised indoors, take them outdoors on a warm day in spring and place them in a spot in your yard with dappled light. Leave them outside for about an hour or two and then bring them back inside. Over the course of the next week or two, repeat this process daily but gradually increase the amount of time your plants are outdoors. If your plants are going to be grown in a sunny area of your garden, also gradually increase the amount of sun that they’re exposed to until they can tolerate 6 to 8 hours of bright light. Once your plants can handle being outdoors for the better part of the day, they’re ready to transplant!

Tip: Moving plants indoors and outdoors can be a hassle, especially if you started a lot of seedlings inside. To make it easier, consider keeping your native plants in a wheelbarrow. This will make it much easier to wheel them outside during the day and then back into a sheltered garage in the evening!

To transplant seedlings, be sure to research how much light and moisture your particular plants need in order to select an appropriate planting location in your garden. If you used a plastic growing pot, carefully wiggle your plant free from the pot, being careful not to damage any roots or its tender stem.

When you’re ready to plant, dig a hole that is as deep as your plant’s pot and 2 to 3 times as wide. Amend the soil you removed from the hole with a bit of compost to inoculate the roots with microorganisms, then locate the plant in the planting hole so it is at the same depth that it was growing in its pot. After that, just backfill the hole with soil, firm the soil around your plant’s roots and then give your new native plant a good, deep drink of water to help it settle into your garden! Some native plants will do better if they are kept in their pots for an entire year before planting on their own in the garden. You will need to pay close attention and keep good records, so you can let others know exactly how you succeeded in growing so many beautiful native plants from seed.