"Is it good to add epsom salt and/or baking soda to garden soil?" It can be good or bad, and no one can really tell you unless they are acting on info revealed by a soil test. Epsom salts (MgSO4 - magnesium sulfate) contains magnesium, sulfur and oxygen, while baking soda NaHCO3 - sodium bicarbonate contains sodium, hydrogen, carbon, and oxygen. The only way to know if you are using an effective strategy to deliver (usually) the magnesium in Epsom salts or the sodium in baking soda is by first determining whether or not these nutrients are deficient in the soil. Only if a soil test shows 1) a deficiency of magnesium, AND 2) the addition of the magnesium in Epsom salts is sufficiently low enough that it doesn't limit the plant's ability to take up other nutrients known to have an antagonistic relationship with magnesium (potassium and calcium, but primarily calcium). Magnesium also acts as a synergist to increase uptake of nitrogen and phosphorous. Sodium, while essential to normal plant growth, is used in minute amounts and is rarely deficient in mineral soils, so it's pretty safe to say it should never be supplemented without a soil test indicating there really is a deficiency. Any micronutrient that should be available at 'trace' levels very quickly becomes toxic at levels higher than necessary.
Usually, it's a less than ideal remedy to try to dose your plants to alleviate a 'suspected' deficiency of any particular nutrient because of how easily it can affect uptake of one or more other essential nutrients. This is true whether we're growing in containers or in the ground (mineral soils), but probably a harder rule when it comes to growing in containers.
When it comes to the objectives of supplementing plant nutrition, and in order to be on target, it's difficult to argue with the idea that our focus should be on ensuring all the nutrients plants normally assimilate from the soil are A) IN the soil and available for uptake at all times,
B) in the soil in a favorable ratio - that is to say in a ratio that mimics the ratio at which the plant actually uses the nutrient, C) at a concentration high enough to ensure no nutritional deficiencies, yet still low enough to ensure the plant's ability to take up water efficiently, and the nutrients dissolved in that water won't be impeded (by a high concentration of solubles in the soil solution).
(B emphasized in the paragraph above because the RATIO of nutrients in the soil, each individually to the others collectively, is very important because of how nutritional antagonisms work. We know using too much magnesium (from Epsom salts) can limit uptake of potassium and especially calcium, which is critical to normal cell formation. Those who feel they regularly need a bloom booster fertilizer (excessively high in phosphorous) run the risk of causing deficiencies of potassium, calcium, copper, zinc, and especially iron. The 'take-away' from the concept that nutrient A can cause a deficiency of nutrient B is the fact that the ratio of nutrients in the soil is a critical part of managing fertility. The best way to avoid that problem is to avoid the temptation to provide your plant with something aimed at a particular nutrient or two, and to use a fertilizer that closely mimics the ratio at which the plant actually uses the nutrients. A very high % of houseplants do best using a fertilizer with a ratio of 3:1:2. The ratio is different than the NPK %s. Fertilizers with NPK %s of 24-8-16, 12-4-8, and 9-3-6 are all 3:1:2 RATIO products. Foliage-Pro 9-3-6 is a superb 'go to' product for almost anything you'd grow in a container.
It's a complete nutritional supplementation program from a singular package and has many attributes not commonly found in other fertilizer products. Ask if interested.
When it comes to mineral soils, and without a soil test, growers are flying blind - no way to know what's appropriate and what isn't. For containerized plants, fertilizing is monkey-easy if you are watering correctly. If you aren't or can't water correctly (so you're regularly flushing the soil) you lose almost all control (over what your plants get in terms of nutrients and when they get them) you would automatically have if you're watering correctly.
Al
