Plant Nutrition

Controlled Release Fertilizers (CRF)

High soluble salts and injured roots have been occurring as a result of improper use of controlled release fertilizers. Controlled release fertilizers, when used properly work well, especially in mixed planters and hanging baskets and for heavy feeders such as petunias. Some growers successfully use a half rate of controlled release fertilizer to supplement their liquid feed program for these crops. However, using too much (not measuring accurately), or not distributing it properly when using it as a top dress can cause problems. Examples of common problems:

Flowable Lime and Potassium Bicarbonate

Flowable lime is being used by growers to raise media pH for some crops such as geraniums and marigolds. A question was asked this week about using potassium bicarbonate rather than flowable lime. Can either be used? Both products are commercially available. The answer is in the fact sheet, "Iron Out" by Paul Fisher, University of New Hampshire (UNH) and William Argo, Blackmore Co. According to UNH research, both materials are highly effective for quickly raising media-pH on crops after planting.

Molybdenum deficiency

This deficiency begins as a yellowing along poinsettia leaf margins, especially on the younger leaves (those on the middle of the plant and upward). Leaf margins become brown and necrotic. Leaves may also pucker downwards. Molybdenum deficiency resembles magnesium deficiency, except that the thin, marginal band of chlorosis is expressed from the leaf tip to the leaf base. Symptoms vary depending upon cultivar. Symptoms on Marblestar (see photo) are striking, but symptoms on other cultivars may be more subtle or lacking. Be sure to check your media pH on a regular basis.

Soil Testing and Disease Diagnostic Labs

With the spring growing season upon us, growers are reminded that floriculture diagnostic labs and soil test labs are available through Universities to help prevent and solve problems. Test growing media early and often to maintain proper pH and fertility. Use a diagnostic lab for early, accurate diagnosis of plant diseases. Catching problems early will prevent the misuse of pesticides, save you money and reduce crop loss. Below is a list of University laboratories in Massachusetts, Connecticut and Rhode Island.


Using Soil Probes for pH and EC Measurements

Use of direct measurement soil probes is a new approach to measuring EC (electrical conductivity or soluble salts) and pH of greenhouse media. Traditionally EC and pH have been measured by collecting media from pots and packs and then analyzing the samples using the 1:2 dilution or saturated media extract methods. Soil probes, however, can be inserted directly in the growing medium for quick, accurate, on-the-spot measurements.

Excess Soluble Salts

Excess soluble salts (high electrical conductivity [EC]) continues to be a problem in spring crop production. High growing medium EC can injure or inhibit the growth of young transplants and sometimes even older, more established plants. Common causes of high EC include: excess fertilizer (too high level [ppm] or too frequent application), subirrigation, root disease, or restricted drainage.

Preventing Iron Deficiency

Iron deficiency symptoms generally show up as an interveinal chlorosis, normally starting at the shoot tips, but often they occur throughout the entire plant. Sometimes the leaves of iron deficient plants turn almost white. Bacopa, calibrachoa, scaevola, snapdragons, and petunia are crops susceptible to iron deficiency. Preventing iron deficiency can be accomplished by controlling pH and using an iron chelate fertilizer.

Iron/manganese Toxicity to Annuals

Zonal geranium, American marigold, and all types of impatiens are susceptible to iron/manganese toxicity, a nutritional disorder associated with low growing medium pH. This problem is sometimes called "bronze speckle" due to the appearance of numerous small brown spots on the leaves of geranium and marigold. Target pH to prevent toxicity is within the range of 5.8-6.5. If the pH is lower than the target range the risk for toxicity increases because at low pH too much iron and manganese becomes available to the plants.

Fertilizing Plants in Outdoor Retail Yards

Plants may need to be fertilized while in outdoor retail yards. Rainfall and watering with plain water will leach out nutrients and plants will exhibit deficiency symptoms such as yellow or reddish foliage. Note that reddish foliage could also be due to recent cool temperatures. If no additional fertilizers are applied, plant quality will quickly deteriorate especially plants that will not be transplanted, such as hanging baskets. Plants in packs, 4-inch and other small containers are also susceptible to nutrient deficiency.

Soil Testing and Disease Diagnostic Laboratories

Prevention and correct identification of insect, diseases and nutritional problems can help you save money by reducing crop losses, improve the quality and marketability of your crops and prevent the application of the "incorrect" pesticide or fertilizer. Here is a listing of the laboratories in Massachusetts, Connecticut and Rhode Island.

Massachusetts University of Massachusetts, Amherst Soil and Plant Tissue Testing Laboratory


Subscribe to RSS - Plant Nutrition