Artificial Soil

What is “Cornell Mix” – used for starting seedlings? It is mostly horticultural-grade vermiculite plus nutrients. To make a peck of the mix, use 4 qts. of vermiculite, 4 qts. shredded peat moss, 1 teaspoonful of 20% superphosphate, 1 tablespoonful of ground limestone plus 4 tablespoonfuls of a 5-10-5 or similar fertilizer. The limestone should be dolomite lime, not high calcium. If this is not available (it is found only in limited areas) add a level tablespoonful of finishing lime to a quart of water and wet the mix with this. Finishing lime is about 50% magnesium. You can substitute 2 teaspoonfuls of Epsom salts for the lime.

A local greenhouse is growing plants in nothing but a 50-50 mixture of peat moss and sand. Is this feasible for garden use? Only under special conditions: liquid fertilizer in a weak solution must be used in place of water for irrigation. In a raised bed on desert sand, this mixture has been used for a vegetable garden in Arizona. Expensive, but better than no garden!

What is gravel culture? The commercial name, “slop culture,” defines it. Plants are grown in gravel with slow drains. Nutrients are dissolved in water and slopped over the plants whenever they seem needed. Although not too scientific, it is easier to use than the practice of true hydroponics, which calls for highly accurate analyses of the nutrient solutions.

A gardening friend uses a mixture of half pet litter and half peat moss for house plants, starting seedlings, and rooting cuttings. I tried it, but it was a flop. What was wrong? Probably the type of pet litter you used. One type is nothing more than dried clay without any treatment. Mixed with peat moss, it forms a worthless, greasy mess. The type that really works (and highly effectively) is made of burned clay that forms grainy, porous particles. To test a given brand, soak in water for an hour. Swirl it around and if all the litter goes into suspension, it is plain clay and worthless. If still gritty, use it. This mixture is good for seedlings up to the time they form the third leaf, but after that they need feeding. For house plants, use a house-plant fertilizer at one fourth the recommended rate, dissolved in water and used for watering plants every time they need moisture.

What is vermiculite? It is a form of mica that, when heated, explodes like popcorn. Treated to 2,500 degrees F. in the process, it is then sterile, holds moisture, and if not over-watered, allows air to reach the roots of plants. It contains a small percentage of potash, but no other plant food. It can be used as a mulch, as an artificial soil base, and is used commercially as a filler in fertilizers. Most lightweight fertilizers have a vermiculite base.

I have used vermiculite for rooting cuttings and starting seeds, but it gets soggy. What am I doing wrong? Watering too often. Vermiculite sops up about three to four times its volume in water, but then can’t hold much more. Use a flat with a window-screen wire bottom and it will drain better.

How is ground sphagnum moss used? Is it mixed with soil? No, it is used as a bed in which to sow seeds so they can be exposed to light without drying out. It contains a natural biotic which prevents damping-off of seedlings. It is a highly valuable material. (It is especially recommended for the fine seeds of azaleas and rhododendrons and other ericaceous plants. It contains no nutrients so the seedlings must be fertilized or soon transplanted.)

Is cod-liver oil a good plant food for flowers? No.

Do castor beans and sumac sap the soil much? Yes, the very luxuriant foliage depletes soils of nitrogen in particular.