GARDENER’S COLUMN: The basics of fertilization | Home & Garden

“I find that a true gardener is not a man who cultivates flowers; he is a man who cultivates the soil.” – Karel Capek

I was finally able to get out and really start cleaning my garden beds. I only had one afternoon but it was lovely. I had to chop down and remove my old flower stems and the extra thick layer of unchopped leaves that always seem to get stuck in the prickiest of bushes. I don’t prune my garden much in the fall as I enjoy the winter interest, wildlife protection, and bird seed that many of my perennials provide. In spring I try not to clean my beds too early, as many insects and various other creatures overwinter in the leaf litter. In fact, I’ve woken up two fat toads and I’m hoping they’ll be warm enough for the next few weeks.

As you review your gardens as you prepare them for the upcoming season, you may consider whether you need to fertilize them. I know it’s not a fascinating subject, but it’s important to know when and how to apply fertilizer. All plants need nutrients to grow, and sometimes we need to replenish, replace, or help release them into the soil. When looking at compound fertilizers, there are three key elements:

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N = Nitrogen promotes healthy leaf growth

P = phosphorus, which is required for vigorous root, flower and fruit development

K = Potassium aids in stem and stem development and plant food production

On a fertilizer bag these three elements are listed in a way like 10-10-10. Nitrogen is the first number, phosphorus is the second, and potassium is the third. If you look at a fertilizer that claims to be for lawns, you will most likely find that the first number is higher than the other two. If you’re looking for one that promotes enhanced bud production, the middle number will be higher. You will also find that some fertilizers are specially formulated for certain plants, such as roses or tomatoes.

There are typically two types of fertilizers: granular/slow-release or water-soluble/fast-acting, and each has its pros and cons. Slow-release fertilizers will feed all season and water-soluble ones can give a quick boost when needed.

Knowing when to fertilize is just as important as knowing what fertilizer to use. It must be applied when the plant can use it – early spring is best for most plants. Keep in mind that many perennial flowers and grasses don’t require a lot of fertilizer. In fact, too much is bad. However, if you have sandy soil without much organic matter, or you notice that your plants are not thriving as they have in the past, light fertilization may be in order. Better yet, get a soil sample done. In many cases, applying an inch of compost or leaf soil to your garden each year will completely eliminate the need for fertilization. If not using compost, use no more than one pound of nitrogen per 1,000 square feet.

Heavy herbivorous plants such as daylilies, peonies, mums and phlox can benefit from spring and summer fertilization. The summer fertilization or side fertilization of fertilizer offers quick access to the required nutrients. You can also side feed perennials—larkspur, daisy, and lungwort—that you prune mid-season to get a second bloom. Annual plants like to be fertilized three to four times during the growing season with a fast-acting, phosphorus-rich fertilizer. Roses are heavy feeders and can be fed weekly with a weak, water-soluble fertilizer.

To learn more about fertilization, visit If you decide to apply fertilizer, always read the package directions on the fertilizer bag or container.

For more information or garden questions, contact the University of Wisconsin Madison of Extension Sauk County office at 608-355-3250 or email


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