Fertilizing Perennials

Fertilizer supplies your plants with mineral nutrients which are “fed” to the plant through the soil.  Plants growing in soils that do not contain all the necessary minerals show nutritional deficiency symptoms such as yellow leaves, floppy stems and brown leaf margins.  One very important thing that I always stress when it comes to adding something to the soil is, get your soil tested. If your soil test shows that you do not need a certain nutrient, use a product that does not contain that nutrient.

Inorganic fertilizer (also known as a synthetic fertilizer, which is manufactured artificially) may not be necessary every year in a perennial bed, especially if you have been diligent in adding compost (an organic fertilizer), but an older bed may need a boost. Organic fertilizers such as leaves, manure and compost can be added each year. They contain less nutrients and are more slow release than inorganic fertilizers.

Most perennials are not traditionally heavy feeders and they do not have as high a demand for fertilizer as something like your lawn does. Depending on the make-up of your soil (soil test), most perennials  benefit from a single slow release fertilizer application just before or at the time that new spring growth appears. It is generally recommended to apply no more than 1 pound of nitrogen per 1000 square feet. Feeding too much nitrogen often causes lush foliage and fewer flowers. Just as a comparison, this is about one fourth of what you may use on your lawn during a growing season. It is better to apply too little fertilizer rather than too much. You can always add more if need be. Roots can absorb nutrients as long as soil temperatures are above 40 degrees farenheit. 

I am particularly fond of the built-into-the-lid spreader of this fertilizer container.

Broadcasting a slow-release granular product is the recommended choice for meeting the perennials season-long nutrient requirements. If you use the “side-dress” method of fertilizer application, apply the manufacturer guideline amount at the general root zone of each plant.  Do not allow the fertilizer granules to cluster at the crown of the plant or linger on the leaves as it may cause burning. If you apply fertilizer in the very early spring the cool temperature of the soil can have an effect on the uptake of certain nutrients in the soil that makes the foliage appear light green to yellow. If this discoloration does not go away as the season progresses, spot treat with a shot of liquid feed to green it up.

There are some perennials  that tend to be heavy feeders such as daylilies, peonies, mums, garden phlox and astilbe. They will benefit from not only a spring feeding, but also from a second application during the summer right after they bloom. Side-dressing with a liquid product that will give immediate availability is the best choice for a summer application of fertilizer. Perennials that you cut back to the ground during the growing season, such as delphiniums, daisies and lungworts will benefit with a spot treating of a liquid fertilizer too. 

It is not a good idea to fertilize in the late summer or early fall as this may cause the plant to put on additional new growth that will not have time to harden off before cold weather arrives.

By the way, now is a good time to get your tools ready for a busy gardening season by cleaning, oiling and sharpening them.

As always, Happy Gardening!

More information about gardening and related subjects can be found online at www.hort/purdue.edu/ext/garden_pubs  The Purdue University Cooperative Extension Service can be reached at 499-6334 in LaGrange Co., 636-2111 in Noble Co., 925-2562 in DeKalb Co. and 668-1000 in Steuben Co.