IF YOU’RE PLANNING to start seeds indoors this winter or early spring, you’ll need seed starting mix or seed starting soil to get started.
While the experts agree in principle on the list of ingredients that should be in seed starting mix, there’s no clear consensus on the optimum recipe. But just about everybody agrees that the two key points are that it should hold moisture and drain well.
Almost everyone’s recipe includes at least some of the following ingredients:
— peat moss or coir
— clean sand
— organic soil amendments or non-organic fertilizers
Worm castings or screened compost are often mentioned as organic amendments. Lime is frequently added to alter the PH and greensand to add potassium. For purposes of this blog, I won’t discuss non-organic alternatives.
Winter harvest expert Eliot Coleman, who starts a lot of vegetables in hoop houses, uses this recipe:
— Three 8-quart buckets of peat
— Three 8-quart buckets of compost
— Two cups of organic fertilizer
— One 8-quart bucket of perlite
Another area of consensus is that even the best garden soil is NOT a good media for starting seeds. The most common problem indoor seed starters face is dampening off and garden soil encourage it. It also drains badly and is difficult for young roots to penetrate because it tends to compact.
Peat and Coir
Peat moss and the more environmentally-friendly coir* are popular because they retain moisture well. Peat is often harvested un-sustainably, ruining peat bogs in the process. Coir, on the other hand, is made from coconuts, a sustainable resource.
Vermiculite also aids in moisture retention and is light weight, making it easy for young roots to move it aside. Perlite holds both water and air. Sand, which must be clean and sterile, promotes good drainage so that seeds and roots aren’t sitting in water for long periods of time. Finally, soil amendments provide nutrients for the seedling once the seed’s food supply storehouse is exhausted.
The big question
Many commercially-available starter mixes do not include nutrients. I guess that the plan is to feed the seedling liquid fertilizer until the plant is planted outside in your garden or repotted. If you plan to keep your seedlings inside for a while without repotting, this could be a problem, especially if the plants are heavy feeders.
Some experts suggest that liquid fertilizer is not enough and you must add soil amendments or chemical fertilizers for good results. But the potential problem with this is the nutrients may promote the development of problem- causing bacteria. The big question is should you use seed starter mix that includes organic soil amendments, such as screened compost or worm castings?
Last year, I started my seedlings in small pet pots filled with Ferry-Morse’s Jiffy Seed Starting Mix. Then, once the seedlings were well established, I transplanted them into larger peat pots with Winterwood Farm planting mix and added Neptune’s Harvest liquid fertilizer at one quarter strength every two weeks. This worked pretty well considering some of the tomatoes were under the lights for as much as six weeks.
One of the brandywine tomatoes from this method was exceptionally productive. I put it under the cold frame early and the tomatoes started ripening around the Fourth of July, and it kept giving until early October, which is really exceptional in New Hampshire.
But I still would like to avoid repotting my seedlings if I can help it. I’d like to keep them under the lights for less time and spare the expense and effort of repotting.
This year, I plan to use paper pots. I’ll fill the bottom quarter of the pot with planting mix fortified with a little of my worm castings. The next two thirds of the pot will be filled with Jiffy Seed Starting Mix. I’m hoping that this will allow me to avoid repotting and, at the same time, protect me from problems with damping off.
I’ll use successive plantings of each variety so that it will increase the chances that I’ll have plants ready for the outdoors that are at the optimum vigor. This will also let me make a course correction if my strategy isn’t working out. I’ll let you know how it turns out.
If you agree or disagree with my strategy, let me know by commenting below.
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