The entire Garden (buildings and grounds) is temporarily closed from Wednesday, March 25 through 9 am on Friday, April 24 in accordance with Wisconsin Governor Tony Evers' Safer at Home order. All Garden events, classes and programs throughout the rest of March and April have been canceled. See updates below.

Seed Starting 101: Everything You Need to Know to Sprout Plants Indoors This Winter

By Lindsay Hendricks, Assistant Director of Horticulture

Although the thought of starting your own veggies from seed for the first time may give you some anxiety, it’s not as difficult as you may think. All you need are a few basic ingredients and you’ll have green sprouts in no time!

seedlings in containers PC Markus Spiske on Unsplash

While most vegetable plants are readily available at your local nursery or greenhouse in the early spring months, they typically carry a limited selection of varieties. By purchasing your own seeds, you have control over which varieties you grow. Not only can you extend the season of cool season crops, but you can also get a head start on growing warm season crops. Here’s what you need to start your seeds:

Growing Medium

Use a soilless media, a potting mix that doesn’t include soil, but has a variety of organic and inorganic materials, as it’s the best option for growing in containers. Plants grown in soilless mixes are also less likely to be bothered by pests or be affected by soil-borne diseases. At the Garden, we use a product called Fafard® 3B mixed with a slow-release fertilizer, Osmocote®.


Get pre-made growing kits or reuse containers (old flowerpots, sour cream containers, paper cups, egg cartons, etc.). Make sure they are clean (sterilize with a 10% bleach solution) and have drainage holes.


For optimal light, a sunroom or south-facing window is your best bet. Seedlings need 6-8 hours of direct sunlight or 12-15 hours of supplemental lighting (ex: an overhead shop light). Not enough light leads to tall, leggy plants that won’t do well when you finally plant them outside in your garden.

garden greenhouse


Starting seeds means you also need some amount of heat to germinate them. Use heat mats, a warm windowsill or the top of the fridge.


A no-brainer, but water helps seedlings germinate (sprout) and grow.


Fill your container with moistened soilless media.

Plant the seeds according to the directions on the packet they came in. Most seeds like to be planted 1-2 times as deep as they are wide and small seeds should be covered with a dusting of fine grade vermiculite. Don’t forget to label which plant is growing in which container with craft sticks or small plastic label stakes.

Water your seeds with a fine mist and keep the soilless media evenly moist until they germinate. Cover the container with a clear plastic lid or plastic wrap to keep the growing environment humid. Once seedlings have popped up, remove the cover. Remember to place your planted containers on a warm growing surface at the start. Once seedlings have emerged, remove them from heat and move into a cooler room. The cooler room should have at least 6-8 hours of direct or 12-15 hours of supplemental light per day.


There are so many vegetables, both cool and warm season, and hardiness zones. Use a calendar like the one found on the Old Farmer’s Almanac website and search by zip code to find accurate start dates for your region.

Cool Season Vegetables

Based on our USDA Hardiness zone of 5a, most cool season veggies such as lettuce, cabbage, kale or onions can be started indoors in March. Peas, carrots, radish, beets, lettuce or spinach can be directly sown outdoors in late April to early May while the soil is still cool.

cucumbers on vine PC Kelly Neil on Unsplash

Warm Season Vegetables

Most warm season veggies like peppers, tomatoes, cucumbers, herbs, squash or pumpkins can be started indoors in April. Corn, zucchini, cucumbers, squash and pumpkins can be directly sown outdoors in late May to early June, once the soil is warm.

Warm season veggies won’t grow in cool soil and require a longer growing season to set fruit. For example, if we waited until the soil warms in late May to early June to plant tomato seeds outside at the Garden, we may get fruit to set by the end of the season but would likely have a killing frost before the fruit actually ripens. So, we start our tomato seeds early indoors to give the plants the best chance to set fruit that will ripen and be ready for harvest by the end of the season.

It’s never too early to start planning your vegetable garden for the next year! Make a list of all your favorite recipes, grow all your ingredients right at home and share with your neighbors or local food pantry.

Sign up for our upcoming Vegetable Gardening for Beginners class on Tuesday, April 7 from 6-7:30 pm for an in-depth workshop on starting your vegetable garden!

For more information on seed starting, check out our how-to video below.