Give Your Seeds and Plants the Best Start

By Dr. Francis Gouin

Plant in most commercial potting media — including Pro-Mix, Sunshine Mix, Farfard Mix, Metro Mix, Jiffy Mix — and your plants get nutrients sufficient for four to six weeks. At that point, you need to begin fertilizing when that nutrient supply is exhausted. If you see bottom leaves yellowing and growth ending, you’ve waited too long.

The problem can be corrected by top-dressing. Nowadays my go-to product is Bloom, a fertilizer made locally from biosolids scientifically processed by the Blue Plains Waste Water facility.

The formula is one-quarter teaspoon each for plants growing in cell packs; one teaspoon for three-inch pots; one rounded teaspoon for four-inch pots. In larger containers, including hanging baskets, top-dress an eight- or 10-inch container with one cup six weeks after planting.

A single top dressing will provide the nutrient needs of most potted plants for eight to nine weeks.

Never blend Bloom in any commercial potting media prior to seeding or transplanting seedlings.

From Scratch

You build in longer nourishment if you blend your growing medium from scratch.

How you make your mix depends on what you’re growing. To achieve optimal plant growth, potting media should have a pH near 6.5 with an abundant supply of calcium and magnesium.

For starting seeds — as you may well be doing this time of year — base your mix on LeafGro. Composted by Maryland Environmental Service from leaves and grass clippings collected in Montgomery and Prince George’s counties, LeafGro provides potassium (K) and beneficial disease-suppressing organisms associated with composted products, while it extends the time-release nutrient properties of your potting media.

Complete by adding an equal volume of peat moss. Peat moss is very acid. Thus for every bushel of peat moss, add 10 ounces of dolomite limestone. Sift the mixture through a one-eighth- to one-fourth-inch mesh. There are sufficient nutrients in the LeafGro to supply the needs of germinating seeds until they are ready to be transplanted.

For potting plants — timely as you transplant seedlings or transfer plants from indoors to out for the summer — add one part by volume Bloom to nine parts by volume LeafGro. Bloom is rich in iron and essential trace elements such as boron, sulfur, zinc, calcium and magnesium.

Complete by adding peat moss and dolomite limestone as above.

There are sufficient nutrients in such a potting media to supply the needs of the plants for at least two months. This potting media should only be used for transplanting seedlings, not for sowing seeds. Soluble salts in Bloom will inhibit small seeds from germinating.

As potting media are rich in organic matter, the solubility of the nutrients is slow. Only time and moisture can assure uniform availability. Blend ingredients thoroughly. If you’re working big, a cement mixer is the ideal mixing tool. Uniform blending can also be achieved by shoveling the ingredients back and forth four to five times on a flat surface. Add water to the blend so that when a handful of the mixture is squeezed into a ball retains its shape. Store the blend in a plastic container at room temperature. It is best to prepare potting media two to three weeks before use.