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How To Plant Seedlings To Encourage Maximum Root Growth

By David Clatterbuck (Dsclatt) - June 2001

This article deals primarily with the planting of seedlings, and more specifically with how deep they should be planted. I have seen many questions regarding “proper” planting depth of seedlings and would like to share the results of experiments I have conducted over the past 3 growing seasons. While I cannot guarantee that my methods will work for you, I can confidently state that these methods have allowed me to grow significantly larger root systems each year.

One of the most enjoyable aspects of Giant Pumpkin growing (for me) is investigating the results of my experiments each year in the fall. I carefully dig up my plants and inspect their root systems to see how big they grew. My results have taught me many things, like the importance of soil compaction and the use of walk boards, and also the importance of burying vines to extend the root systems. Here are my recommendations and reasons for proper planting depth:

Question:...How deep should I plant my seedlings?
Answer:...As deep as possible, right up to the bottom of the cotyledons (the seed leaves).
Why?...Because new roots will grow out of the sides of the seedling stem along the entire length of the buried section.

Now let’s take that thought one step further...

If the seedling were taller (had a longer stem), it would mean that the potential would exist for more roots to be able to develop along the shaft. So the next logical question would be: How do I make the seedling longer / taller? The answer is rather simple: Light depravation.

I have noticed for many years that each spring, when my wife starts all of her flower seedlings indoors, some of them always seem to get very long and “leggy”, and eventually fall over because they are too tall to support themselves. The ones that seem to always do this, are the ones that are furthest away from the light source (fluorescent grow lights). This gave me the idea of experimenting with planting depths of pumpkins seedlings. It may sound a little controversial, but here’s what I do.

First of all, forget the peat pots. Use large coffee cans with both ends cut off and the plastic lid as a bottom. If you don’t have coffee cans, use 1 gallon or 2 gallon plastic pots (from shrub seedlings, or any deep container) lined with saran wrap (to allow for easy removal of the seedling later, allow the saran wrap to extend a few inches beyond the pot/can on each side). Fill the container only 1/3 of the way with seed starting mix, and plant your seed approximately 1 inch deep (after filing and soaking).

Put a light source over the container (I use the standard “shop light” with a built in clamp) keeping it close enough to the container to provide heat, but far enough away so that you don’t cook your seed, and then wait for the seedling to sprout (3 to 5 days).

When the seedling pops through the surface and the cotyledons emerge, raise the light up about two feet. Wait 24 to 36 hours (keeping the light on the whole time) and then add more potting soil to your container, filling it up to the bottom of the cotyledons. Water the new soil, and then repeat the process over again, raising the light up another foot, and then waiting 24 to 36 hours, then add more potting soil and water it again. The light should stay on through this entire process.

You will keep repeating this process until the soil is close to or even with the top of the container. Once you reach the top of the container, your seedling should be about a week old or so, with it’s first true leaf formed (and maybe the second) and should be ready for planting in about a week. Wait until the seedling is about two weeks old before you plant it to allow the “extended root system” time to get established.

When you plant the seedling outside it should again be buried to a depth of soil that is just below and/or touching the bottom of the cotyledons. If you were to remove all of the dirt from the seedling at this time, you would discover new roots emerging from the sides of the extended stem along it’s entire length.

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