Gardening While Isolated: Transplanting and Fertilizing Your Seedlings

The Gardening While Isolated series continues with a look at transplanting and fertilizing

May 19, 2020, 11:53 am | Kathleen Delate, Bob Turnbull

AMES, Iowa – Once indoor-grown seedlings have an extensive root ball (roots fill the entire cell when pulled from the flat) and all chances of frost have passed, it’s time to transplant the vegetables into your garden.

In this edition of Iowa State University Extension and Outreach’s “Gardening While Isolated” series, horticulture specialists describe the best options for transplanting and fertilizing.

If your transplants were purchased from a garden store, make sure the leaves are a healthy green (not yellow or nitrogen-depleted) and free of insects and disease before planting. Because vegetables need a sunny, well-drained growing area, prepare a tilled, raised planting bed in your garden so water will easily drain. Tips on how to plant and fertilize your transplants can be observed in the latest horticulture team video.

Composting made easy

Compost and composted manure form the backbone of organic vegetable fertilization. Organic gardening emphasizes building healthy soil by increasing soil organic matter, which can be augmented with homemade or purchased compost or composted manure. Compost can improve drainage and aeration of soil, along with increasing earthworms and beneficial microorganisms, which help break down and recycle nutrients for the plants. Compost can be made by creating compost piles in bins or boxes in your backyard, or use a composter, such as the Earth Machine.

squash transplant.Composting is an aerobic or oxygen-requiring process in which microorganisms, including bacteria, fungi and actinomycetes, consume oxygen, while feeding on organic matter supplied. Typical feedstocks for composting include kitchen wastes, yard wastes like grass clippings, and hay or straw. Any grass clippings with herbicides should not be used. The best composts have a carbon-to-nitrogen ratio (C:N) of 25-35 parts of carbon to 1 part nitrogen (25:1) so that excess energy is not expended by microorganisms in breaking down highly carbonaceous feedstocks. A C:N ratio of 40:1 or higher can immobilize nitrogen and slow the composting process. It is not recommended to add any type of manure to a home compost system due to the potential for contamination.

Composting stabilizes nutrient content, meaning nutrients will be released slowly over time. The time required to produce a mature batch of compost ranges from 6-8 months, and a rich, humus-like material, with an earthy smell is produced at the end of the cycle. Commercial systems, described below, can be set up to mix manure and stabilize it to avoid odors and contamination issues. Sanitized, composted manure can be purchased from a garden store and used in place of homemade compost on a 1-to-1 ratio, mixing in two inches of compost in a four-inch hole dug for your transplant.

Compost for certified organic operations

If growing and selling produce as certified organic, follow the United States Department of Agriculture’s National Organic Program rules, which include exact specifications on temperature (piles must reach 140 degrees Fahrenheit) and turning requirements (after temperatures drop) in creating compost. Most commercial organic producers or compost operations will add a manure source to their compost to increase the nutrient content.

Dairy manure, for example, contains 2-3% nitrogen, and the other 12 essential plant nutrients: phosphorous (P), potassium (K), calcium (Ca), magnesium (Mg), sulfur (S), manganese (Mn), copper (Cu), zinc (Zn), chlorine (Cl), boron (B), iron (Fe), and molybdenum (Mo). Composts are established in windrows, which can be routinely turned to increase oxygen and microbial breakdown in the pile.

To be on the safe side, most organic farmers follow the “raw manure rule,” even for composts, and apply any compost with manure at least 120 days before the harvest of any vegetable. Sending a compost sample to a soil analysis lab is recommended, especially if developing a commercial product.

Other organic fertilizers

One of the easiest, most economical liquid organic fertilizers is fish emulsion. Composed of recycled fish processing wastes, this fertilizer’s nitrogen content usually ranges from 2-3% N. You can fertilize once at transplanting, and then on a weekly basis until fruit set. Organic compliance for purchased materials can be verified if products contain an OMRI label — Organic Materials Review Institute.

Other animal-based organic fertilizers, such as blood meal, feather meal and fish meal contain 10-14% nitrogen, and require additional attention while applying, to avoid excess nitrogen pollution. Other plant-based organic fertilizer sources, such as cottonseed or soybean meal, contain 6-7% nitrogen, but may not be readily available in organic or non-GMO forms.

Always check the label for application details and recommended rates. If any signs of nutrient deficiencies develop, you can send plant samples to the ISU Plant and Insect Diagnostic Clinic.

Mulching to protect seedlings

Placing straw mulch around your transplanted seedlings provides protection from wind and conserves soil moisture. Additionally, the mulch can break down over time and increase soil organic matter. Oat, wheat or prairie grass straw can be purchased from garden stores or from local farms.

Ideally, straw is free from grain seeds. It is not recommended to use wood chips or bark with annual crops, as nitrogen can become immobilized when microorganisms break down these more carbonaceous materials if mixed with soil. Some woody plants, like black walnut hulls, cannot be used for vegetable crops, due to the presence of an inhibitory chemical, jugalone.

Mulch should be applied at four to six inches in depth to help prevent sunlight from reaching any weeds germinating in the garden. Mulches can be reapplied throughout the season and turned under in the spring before the next crop.

The products and suppliers mentioned in this release are for example only. No endorsement of these products or suppliers is intended.


Crop Rotations, Composting and Cover Crops for Organic Vegetable Production

Growing Organic Vegetables in Iowa

Using Organic Agriculture and Sustainable Crops and Livestock in the Local Food System


Original photo: Transplanting squash.

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