Starting Seeds Indoors
By Sarah Holdner
UNH Master Gardener Volunteer
Although it may seem daunting at first, successfully starting your own seeds is a rewarding and attainable goal for any gardener. With a few supplies, determination and a little bit of creativity, you are just steps away from making your home and garden a little greener.
For budding gardeners, or those who have yet to delve into this exciting horticultural activity, here are some guidelines for successfully starting seeds indoors:
Timing is Everything
Although it may be tempting to start all your seeds as soon as cabin fever starts to set in, it’s important to time seeding with your transplant date in mind. Look at the information on the seed packet to determine the ideal transplant time and then use that date to calculate when the seeds should be started.
In New Hampshire, it’s usually safe to transplant tender seedlings after Memorial Day; however, frost can still occur after this date. For example, tomato seedlings should be sown five to eight weeks (depending on variety) before the desired transplant date. Therefore, a cautious gardener who wishes to transplant on June 1 shouldn’t seed tomatoes before April 1.
Plants that are seeded too early may become root-bound or flower before transplanting, which may weaken them in the long run. Some cold-tolerant vegetables such as kale, spinach, broccoli, carrots and peas can be planted in the garden earlier, so you have more flexibility on when you start them.
Starting your own seeds doesn’t have to be expensive. In fact, it can be one of the most economical ways to garden. All you need are the following materials:
Clean containers with good drainage: You can purchase these or get creative with your recycling. For example, a yogurt cup with holes punched in the bottom is an excellent option.
Sterile potting medium: Avoid using old potting or garden soil, as either may contain pathogens or pests that can harm delicate seedlings. It’s best to use a mix specifically formulated for seedlings.
Consistent light source: Setting up in proximity to a south-facing window or under a shop light is ideal. Plants without enough light tend to stretch and become “leggy” and weak. If you choose to use artificial light, 40-watt cool-white or full-spectrum fluorescent lights are an excellent option.
Warm place: Most seeds require temperatures between 65-75 degrees Fahrenheit for germination. A heating mat can help you achieve this.
Water: Keep the soil moist but be careful not to water too deeply as overwatering may induce rotting. You may find the use of a handheld sprayer on the “mist” setting is a useful tool for watering your seeds and seedlings.
Seeds: Seeds that are less than a year old will germinate most reliably, though older seed can still be used, albeit with lower germination rates. Older seeds can be tested to determine whether the germination rate will be suitable.
First and foremost, choose seeds for plants that you will enjoy. One major benefit of starting your own seeds is that you have access to a wide selection of new and unusual varieties that would not be available to you as starts.
It’s advisable to buy seeds from reputable companies based in the Northeast, as these plants will most likely be adapted to the climate in New Hampshire. If you plant seeds you’ve saved yourself, be prepared for surprises. Cross-pollinated seeds, or seeds from hybrid plants, may not be the same as their parents.
Some seeds do very well when directly sown in the garden, such as peas, beans and root vegetables like carrots or radishes. It may be best to put your effort of starting seeds indoors into other kinds of plants such as tomatoes, cole crops (broccoli, Brussels sprouts, cabbage, cauliflower), annual flowers, herbs, lettuce and even onions. Squash and cucumbers can be started indoors, though it is best to use biodegradable pots so that their roots are undisturbed during transplanting.
Once you’ve organized all of your supplies and the timing is right, start by wetting your potting mix. Make sure it is evenly moistened before adding it to your containers.
Next, plant your seeds in the amount and to the depth specified on the package. Some seeds require light or darkness to germinate — check for this information on the package to determine whether to cover the seed with medium or not. A general rule is that seeds can be planted twice as deep as they are wide if you do not have clear directions.
Label seeded containers as you go. Many seedlings are difficult to tell apart, especially if you choose to grow multiple varieties of the same kind of plant.
Make sure to water regularly so that the soil is evenly moist, but not wet. A misting spray bottle is a great way to gently water. Stronger streams may disturb the soil and seeds. Many gardeners choose to cover their seeds (leaving room for growth) with plastic wrap to help keep moisture in.
Put your pots in a warm place in the light of a window or under artificial lights. If using artificial lights, leave 6 to 12 inches of space between the seeds and the artificial lights, and continue moving the light up as the plants grow.
After the plants develop their true leaves, fertilize with quarter- to half-strength balanced fertilizer that contains nitrogen, phosphorus and potassium. Too much fertilizer may burn the roots, so measure carefully.
Hardening Off and Transplanting
About a week before transplanting, seedlings must be hardened off. This means slowly introducing plants to the outdoor environment so that they won’t be damaged by the wind, changes in temperature, or burned by the sun.
Place the seedlings outside in a protected area for a few hours each day, increasing the time spent outdoors each successive day. A structure with shade cloth makes this process easier, so that instead of moving the plants to a shady area or back indoors you can simply cover the plants when the exposure time for that day is complete.
Decrease watering, but don’t allow the plants to wilt. Do not put seedlings outside when the temperature is below 45 degrees or if it is very windy.
Once the plants have acclimated to being outdoors, it’s time to plant. Dig a hole to about the same depth as your seedling container and carefully remove the plant (unless you are using a biodegradable pot), placing it in the hole.
Brush soil around the new plant but be sure that you do not cover the growth point (where leaves begin to first grow on the stem). Water deeply.
Finally, congratulate yourself on a job well done.