Starting Seeds Without Dirt

Winter is a time of rest for the gardener, and midwinter is the time for dreaming. With seed catalogs arriving in the mail almost daily, the dream of this year’s garden begins to take shape. The newest tomato variety or flower color pictured on the cover will catch my eye, and I have to work hard to limit my selections. I usually choose a few of the more unusual varieties that may not yet be available from the local garden centers and start them from seed. If you only want a few flowers, a garden center is the best choice for plants in the spring, as well as for new ideas for gardens. But if you would like to see an ocean of impatiens or petunias in your yard or on your patio, you should consider starting from seed.

Starting seeds without dirt by using OasisĀ® Rootcubes will make seed starting easier. Oasis Rootcubes are similar to the familiar floral foam that is used in cut-flower arrangements. A sheet of 104 pre-punched Oasis Rootcubes fits into a standard black tray (10″x 20″). Oasis Rootcubes are a sterile, pH-balanced media, with a high water-holding capacity as well as excellent aeration and drainage properties. Additionally, a two-week supply of starter fertilizer is incorporated into the cubes, making them an ideal medium for seed starting.

Oasis Horticubes have no starter fertilizer and have a looser structure which makes it ideal for starting seeds.

OASIS Rootcubes or Horticubes

Step 1 – Planting the Seeds

Thoroughly saturate the sheet of Oasis with plain water prior to planting. Drain off any excess water by tilting the tray. Plant two seeds per cube, and cover lightly with perlite or small pieces of oasis (from an extra cube). However, it is not always necessary to cover seeds planted in the pre-punched Oasis cubes. The most notable exception would be lettuce seed which requires light to germinate. Pelletized seeds work well but may need to be pressed into each hole. Remember to stick a plant label into the beginning of the row of each new variety that you plant as you go along.

Step 2 – Keep Seeds Moist and Warm

Keeping the seeds evenly moist and warm is important for good seed germination. Oasis soaks up water easily from the bottom of the tray, and watering from the bottom will not dislodge or disturb the seeds or seedlings. A plastic humidity dome may be placed over the tray until the seeds begin to germinate. Remove the dome at least twice a day to allow fresh air to circulate around the seedlings. As soon as the seeds begin to sprout, remove the dome.

The best temperature for seed starting is between 70 and 85 degrees. Most seeds will germinate at temperatures a bit lower, however, they will germinate faster with warmer temperatures. Many types of seeds, such as tomatoes and peppers, require warm root zone temperatures to germinate. This may be achieved by the use of a propagation heat mat. Heat mats are available with or without a thermostat. The newer types of heat mats are less expensive and are calibrated to raise the temperature approximately 10-15 degrees above room temperature. This works well. However, be sure to check periodically to be sure that your seedlings do not get too warm. Also, adding heat will cause the water in your Rootcubes to evaporate faster, so check the water level more often as well. If you feel that your seedlings are getting too warm, create an air space between the tray and heat mat. Be sure that the temperature does not exceed 90 degrees. Larger heat mats with external thermostats are another option.

Step 3 – Provide Adequate Lighting

Lighting for seedlings is extremely important. If you have a greenhouse, conditions are ideal for seed starting. Indoors, fluorescent grow lights may be used. You will need to keep fluorescent lighting directly over each flat no more than 6 inches above the trays. Once the seedlings are between 4 inches and 6 inches tall they will require more light. An HID Metal Halide Growlight is a worthwhile investment that will pay for itself in a few years of starting your own seeds. A 250-watt Metal Halide System will give you enough light for six or more flats of 104 cubes. You will probably find that one 250-watt Metal Halide light will work better and be more cost-efficient than a multitude of fluorescent lights. Seedlings can be maintained under a HID grow light until you are ready to move them outdoors.

Step 4 – Care of the Seedlings

After the first true leaves appear, remove the less vigorous of the two seedlings in each rootcube with scissors. Begin to fertilize the seedlings with quarter strength fertilizer. I prefer to use fertilizer every other time that I add water to the Oasis. Any general purpose, complete fertilizer will work. I use nutrients that have trace elements such as Dyna-Grow or the General Hydroponics Flora Series. Organic fertilizers, such as seaweed or fish emulsion, may also be used.

Step 5 – Harden Off Seedlings

Seedlings need to adjust to outdoor growing conditions gradually. Full sun, excessive wind, and hard rain can do damage to young seedlings. Move them outside to a protected area and gradually increase their exposure to the elements. Move them indoors at night until the nighttime temperatures are above 45-50 degrees.

Step 6 – Transplant Seedlings

Once your plants have been hardened off in the Oasis cubes, simply break them apart before transplanting them in your garden, container, or hydroponic system. When transplanting, keep in mind the size of the mature plants to avoid overcrowding. To reduce transplant shock, water plants well with a solution of Superthrive. I am sure you will agree that using Oasis cubes will make the messy chore of seed starting much easier.

Scroll to Top