Figuring out when to plant vegetable seeds indoors isn’t rocket science, but can be a little mind bending. It involves counting backwards. To determine when to plant seeds of a particular vegetable or flower indoors, first find out when it should be planted in the garden. Visit https://bookstore.ksre.ksu.edu/pubs/s51.pdf to see our Kansas Garden Guide which has a nice planting calendar to use for this purpose. Then you’ll need to find out how many weeks each crop should be grown indoors and count backwards from the actual planting date to learn when to start seeds indoors.
To simplify, here are some suggestions. Broccoli, cabbage, Brussel sprouts, cauliflower, kale and collards should generally be started indoors around mid-February. These cool season plants are grown indoors for about 6 weeks and then planted out in the garden in late March or early April before the final frost date occurs. Other cool season crops like peas, lettuce, or spinach are often direct seeded into the garden around mid to late March depending on temperatures.
Tomatoes, peppers, and eggplant are all started indoors in mid to late March and usually planted in the garden in early May.
Melons, muskmelon, cucumbers, squash, and pumpkins should be started indoors in late April and planted in the garden in mid to late May when soil temperatures are warm. These crops can also be direct seeded into the garden if desired.
Tips for growing transplants
Sowing Seed: Do not use garden soil to germinate seed as it is too heavy and may contain disease organisms. Use a media made especially for seed germination. Seed must be kept moist in order to germinate. Water often enough that the media never dries. Using a clear plastic wrap over the top of the container until the new plants emerge can reduce the amount of watering needed.
Light: Most plants will germinate in either darkness or light but some require darkness, so read the package to make sure. All plants require adequate amounts of light once emergence occurs. South facing windows may not provide adequate amounts and so fluorescent light fixtures are often used. Suspend the lights 2 to 4 inches above the top of the plants and leave them on for 16 hours each day.
Temperature: The temperature best for germination is often higher than what we may find in our homes especially since evaporating moisture can cool the germination media. Moving the container closer to the ceiling (top of a refrigerator) can help but a heating mat is best for consistent germination. After plants have germinated, they can be grown at a cooler temperature (65 to 70 degrees during the day and 55 to 60 degrees at night). This will help prevent tall, spindly transplants.
Plant Movement: Plants react to movement. Brushing over the plants with your hand stimulates them to become stockier and less leggy. Try 20 brushing strokes per day. However, brushing will not compensate for lack of light or over-crowding. Plants grown under inadequate light will be spindly regardless of any other treatment.
Hardening Transplants: Plants grown inside will often undergo transplant shock if not hardened off. Plants should be hardened off by moving them outside and exposing them to sun and wind before transplanting occurs. Start about two weeks before transplanting into the garden and gradually expose the plants to outside conditions.