Indoor Seed Starting Basics

Starting plants from seed indoors can be a great way to give ourselves a head start in condensed Montana growing seasons. We can customize plant varieties to broaden the possibilities of our gardens with some flexibility.

Before starting seeds indoors, it is important to note that not all plants respond well to being transplanted. Root crops and plants with larger seeds (generally larger than ¼ inch) usually perform best when they are directly seeded into the landscape. Broccoli, Cabbage, Kale, Pepper, and Tomato are examples of plants with smaller seeds that transplant well.

Seed packets can contain helpful information, including cultivar, days to germination, spacing, planting depth, thinning, etc. These packets can also be retained for growth or success records. Some seeds can remain viable for multiple years, but for the best chance of successful germination, purchase and use seeds within a year of the packing date. To see if seeds are still viable, do a ragdoll test by wetting a paper towel, placing 10 seeds on the paper towel, and placing it in a plastic bag in a warm location to assess germination rates. If only one or two out of 10 seeds germinate, the germination rate would be 10-20 percent. Account for the germination rate when sowing seeds (consider sowing seeds at a higher density than recommended on the seed packet).

Indoor seeds should be placed in a sterile, soilless medium or potting mix (without any fertilizer). These sterile soilless media are lightweight and free from disease-causing organisms and weed seeds (which allow for healthy seedling growth free from competition). A good soilless seed-starting media should retain moisture, allow for successful drainage, and have a uniform texture for good seed contact. Purchase pre-made mixes, or rehydrated seed starting pellets, or create a mix using a variety of materials, including sand, vermiculite, perlite and shredded coconut coir or peat moss. There are several recipes available (a good starting point is three parts peat moss or coir to one part perlite), but a good rule of thumb is to ensure the mix allows adequate moisture, good drainage, space for oxygen (pore space), and structure to support plant growth (imagine the texture of a light potting mix).

There are countless containers available for seed starting, but make sure they are clean and sterilized, have good drainage, and are deep enough to accommodate seedling roots during the time they will grow indoors before transplanting. Containers with individual cells for seedlings or rehydrated seed starting pellets can help reduce the amount of root damage during transplanting as opposed to larger containers, which require more root handling to separate seedlings for transplanting.

GERMINATION

Seed germination depends on a variety of factors, including water, oxygen, light, and temperature. Getting a good balance of these factors is critical to successful germination and healthy seedlings. Water is the key to germination, and maintaining enough moisture can be a balancing act. Seeds need constant contact with water (either through moist growing media or regular misting).

Maintaining a high humidity in the growing environment is also important for germination. Create a miniature high-humidity environment by using clear plastic dome-like lids or bags to cover seeds until they germinate. Anything that restricts oxygen should be removed after germination. Once seedlings emerge, oxygen becomes very important. Make sure seedlings have access to oxygen by maintaining good drainage (preventing over-saturation). Light requirements of individual seeds should also be considered during germination. While some seeds require light to germinate, some may require darkness, and others may have no preference. Carefully read the seed packet to determine if the seed has a light preference and treat it accordingly. Seeds that require light to germinate should be placed on the surface of the growing media, whereas seeds that require darkness should be covered with a very light layer of the media (no more than twice the diameter of the seed). The temperature range of the growing media can also impact the success rate. Some seeds have specific temperature requirements, but for many seeds, aiming for a growing media temperature of 65-75 F is sufficient. To maintain this temperature, use waterproof heating mats or a warmer location in the home. Use a thermometer to track the temperature and adjust accordingly.

SEEDLINGS AND TRANSPLANTS

Once germinated, seedlings require supplemental lighting (such as fluorescent or LED lights) to grow. Aim for 16 hours of light per day to prevent weak seedlings. Seedlings also need nutrients for optimal growth, so fertilizing is necessary during this time. Once seedlings begin to grow past 1-2 inches, use a diluted soluble fertilizer at a half-label rate, and adjust accordingly as seedlings grow.

Harden off all seedlings by reducing watering frequency and slowly transitioning them to outdoor conditions for a few hours a day, then increasing the outdoor time over 1-2 weeks. Once seedlings are hardy, they can be safely transplanted with a reduced likelihood of transplant shock. Transplant healthy and vigorous seedlings into the garden based on their cold hardiness. Warm-season seedlings (like tomatoes and peppers) should be transplanted after the threat of frost has passed.

Starting seeds indoors can be a rewarding activity for gardeners of all experience levels. Experiment with a variety of techniques and reach out to local Extension resources for assistance.

Abiya (Abi) Saeed is the MSU Extension Horticulture Specialist.