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I had a planter full of a nice soil mixture but let it go dormant and dry out for a year or two. Recently I have kept it around some other plants, exposed it to more light, and applied fertilizer (fish-based fertilizer then a couple of days later worm castings from kitchen scraps).

Can seeds be planted in that soil now without harm or are they better off being planted after the freshly-fertilized soil rests longer? If I should wait in between fertilizing and planting, how long?

The seeds I'm interested in planting for this soil are a mix of salad greens. The concern with planting the seeds too soon is that the fresh fertilization will somehow injure the seeds.

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It sounds like you should be fine. Worm casings are fine, as is, and if the fish-based fertilizer is sold as a fertilizer, read the instructions. If the instructions call for adding it to growing plants, and not just as a soil amendment that has to break down, then it will be fine.

The place where you have concerns is when you are adding stronger soil amendments - fresh, not composted manure has the capacity to cause nitrogen burn, or artificial fertilizers in higher than recommended concentrations.

It sounds like what you added is friendly for immediate use for plants, though, again, check the instructions for the fish-based fertilizer to make sure you didn't add too high a concentration or amount for the container size.

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If you want a better chance of success you will dump the OLD soil out and replace it with POTTING SOIL. Do not use garden soil. Do not put rock or gravel below the soil and above the drainage hole. Raise the bottom of the pot off any surface to improve drainage. Potting soil is cheap. Garden soil does not belong in pots unless you ABSOLUTELY are unable to get potting soil because you live in the middle of Alaska with no Home Depot or Grocery store. Or India I have found. There are other answers here that go into depth about the WHYs. Fertilizer should always be balanced, compost and fish fertilizer do not meet the qualifications. Fish fertilizer is good but really only those that understand fertilizers should ADD anything to their POTTING SOIL other than an extended release balanced fertilizer. If you add a balanced NPK plus micro nutrients that fish fertilizer which adds nitrogen might make the nitrogen higher in percentage to the phosphorous and potassium and THAT might cause your plants harm. Lettuce needs higher nitrogen because you want the leafy stuff. Too high of nitrogen and plants will not flower and fruit well.

Fertilizer, fish emulsion, blood meal and all the other additives are NOT food for your plants. They primarily give soils the chemistry plants HAVE to have to do photosynthesis and make their own food. Fertilizer does nothing to 'revive' soil. Dump this old soil in your garden. Only decomposed organic matter improves soil's tilth and feeds the soil organisms. That is the only way to improve GARDEN SOIL. Potting soil is different and you are correct, baby plants should not have fertilizer until they are a bit more mature.

Potting soil is sterilized and made for pots. Actually very little soil is in potting soil. And don't get potting soil with fertilizer or any moisture holding gimmicks like sponges or gels. Potting soil is cheap and gives you a chance for success. I know an awful lot about plants, soils, fertilizer and I would NEVER make my own potting soil although I DO know how.

What was planted in your old soil? What insect eggs or pathogens are harbored in that soil? Sure plants will grow but not as vigorously as they would in a pot in potting soil. Success will be iffy. Lettuce is fun to grow.

Please start by germinating seeds in tiny pots...made to start seeds. Using fresh out of the bag potting soil. Germinating or planting too tiny starts into a large pot with a large body of soil, will not be very healthy and is basically a no no. Start seeds in those little peat pots and when the roots show through the bottom UP POT to a size larger....3-4" pots. Use fresh potting soil and now is a great time to add an extended release fertilizer. OSMOCOTE, 14-14-14 is what I recommend even though it is by Scott's. You will need to add a little more when up potted to their larger pot but after than you are done with adding fertilizer.

When the roots show through the bottom in these larger pots, then I would try planting into a larger pot. I usually end up transplanting 3 - 4" starts into a 1 gallon pot (6") for all single vegetables and leave my large pots for tomatoes, or potatoes or squash. `1 gallon pots grow a great head of lettuce, peppers, basil... Do not water deeply until the plant has enough roots integrated into the body of soil (helps to remove water, allowing more air). Then you should start watering deeply and allow the soil to dry (inch below surface dry) before watering again. The larger the plants get and taking into consideration warmer weather the more they will need water but NOT everyday.

  • Thanks for all the info. For other herbs and vegetables I am using the method you described. In this case I have a mix of salad green seeds and hope to fill this window-sill style rectangular pot with them, without nursing the many plants in smaller pots first. I understand potting soil is easy to buy but I am trying to learn how to produce my own soil and reduce external inputs I bring into my household/garden, so if I can try to make my existing soil work using other resources I already have (worm castings, leftover fish emulsion, fish tank water) I want to give that a go. – cr0 Apr 27 '17 at 14:08
  • Very different from the answer I gave, but that's not necessarily a bad thing. Lots of useful info in there. +1 – PoloHoleSet Apr 27 '17 at 14:30
  • We used to have free compost from our county yard waste site. They'd incorporate manure from local dairy farms, and had huge tractors that would regularly turn the piles, an then you'd be directed to the piles that were done. I liked to incorporate that into my containers, so I'd cook the soil in roasting pans on my grill, mix it with potting soil and perlite, and that worked pretty well for me. – PoloHoleSet Apr 27 '17 at 14:32
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    If it makes you feel better, note my the language in my comment - "We used to have free compost...." I make my own in a bin and use lasagna gardening as the base for my raised beds, now. :D The county discontinued the service when the main city in the county decided to sell their yard waste to a producer of bagged soils, instead. So, your caution about local yard waste compost vs enthusiasm about bagged soil may not be warranted. – PoloHoleSet Apr 27 '17 at 19:24
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    "Bagged soil" producers also sell bagged "compost" or "composted manure" as well as "top soil" at most garden stores and lumber yards. – PoloHoleSet Apr 27 '17 at 19:38

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