Thursday, February 3, 2011

Which Potting Medium is Best for Starting Tomato Seeds?

Choosing a potting medium wisely is an important step to take when growing tomatoes from seeds. The potting medium you select will be home to your tomato seedlings while they sprout and during their first few weeks of life.

A potting medium’s main jobs are to get the seeds to sprout and to keep new plants disease-free. There are three kinds to choose from: garden soil, potting soil, and potting mix.

Garden Soil
When it comes to starting tomato seeds, garden soil (dug up from your outdoor patch) has three drawbacks: extra seeds, texture, and undesirable organisms.

First, garden soil is full of weed seeds. Good sprouting conditions mean weed seeds will compete with tomato seeds for space, light, nutrients, and water. Moreover, garden soil’s texture is heavy. It compacts easily in small containers, which prevents good circulation and can choke seedlings. Worst of all, garden soil is crammed with bacteria and fungi, which are the main culprits in damping off disease. Damping off has claimed many tomato crops as soon as they sprout – or even before, by killing off the seeds.

The best thing that can be said about garden soil as a seed starting medium is that it’s free.

Potting Soil
Check labels carefully when shopping for potting mediums at your local nursery or home improvement center. Note some are labeled “potting soil” and others are “potting mix” – a subtle difference on packaging, but a huge difference in content. In general, potting soil is heavier than potting mix. Content listings reveal additives like clay, sand, and compost. While these combinations are excellent for established plants, they are a less helpful environment for seeds and newly-sprouted seedlings. When potting soil compresses with planting and watering, there are fewer air pockets, which make it harder for seeds to sprout.

In addition, most potting soils have a higher percentage of fertilizer than potting mixes. Tomato seedlings don’t need to be overfed. They acquire their initial nutrients from the seed. In fact, too many nutrients for brand-new seedlings can cause them to grow too tall and thin too fast.

Potting Mix
Potting mix is the best choice for starting tomato seeds. It is sterile, lightweight, holds water, and is low in fertilizer. Purchase commercially-prepared potting mix or make your own. A good prepared potting mix contains ingredients like sphagnum peat moss, vermiculite, and perlite. Sphagnum peat moss has anti-fungal properties that help keep seeds and seedlings disease-free. Vermiculite and perlite provide air pockets to keep the mixture light and allow circulation, while still retaining moisture.

Whichever potting medium you choose, prepare it before planting seeds by adding warm water and stirring until the mixture is evenly damp. Press it lightly into your seed starting containers, plant tomato seeds, and get ready for a wonderful tomato crop.

About the Author
Kathy Widenhouse is a contributing writer for Mike the Gardener Enterprises and owner of Tomato Dirt (, a leading source for information on growing tomatoes and using them.

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