Set aside measuring tools that are only used with fertilizers.

Set aside measuring tools that are only used with fertilizers.

There comes a time when gardeners have to think about fertilizing their plants — a topic that makes us squirm, primarily because there are so many choices out there. How much? Organic or inorganic? Slow or quick release? When should we fertilize?

Then there are those three numbers on the bottle or box.

The first number indicates how much is nitrogen, the second denotes the phosphorus measurement while the third refers to the potassium content. All plants need these three elements — some more than others.

Unlike the other two, nitrogen moves quickly through the soil. A thunderstorm releases the nitrogen locked in the air, explaining why the garden can look so refreshed after a storm. Nitrogen promotes green growth, desirable when pertaining to hostas, but not as wanted to the same degree for roses, as we want to promote blooms rather than green growth in roses.

There are several general rules for good fertilizing practices:

  1. Give the plant fertilizer when it’s growing — not when it’s stopped growing for the season. For example, hostas grow in the spring but stop growing by mid-summer. In this case, a time-release fertilizer is not desirable because the plant will receive the fertilizer long after it can profit from it. It pays to know when the plant is growing and when it’s approaching slumber time. For hostas and other plants preparing for dormancy by mid-summer, I’d use 10-10-10 in the spring when the plant is emerging.
  2. Don’t fertilize sleeping plants. Roses start preparing for winter in late August or early September, so hold off on the fertilizer. Camellias go dormant in the summer while hellebores start to wake up in late September and October.
  3. Some plants don’t require fertilizing if grown in decent soil. Echinaceas are tough prairie plants and prefer a lean diet. Do you really want more hellebore babies lurking around the mother plant?
  4. Composted manure is good for many plants, but the key word is “composted,” as fresh manure will burn most plants.
  5. Always read the instructions on the box. More is not better and can be detrimental.

Roses, being heavy feeders, need fertilizer if they are going to look their best. The only roses that don’t require fertilizing are the species roses (such as Rosa roxburgii, the chestnut rose, and the Lady Bank roses) and the rosa rugosas. Most of these roses only bloom once.

When fertilizing roses, use one that is specifically for roses as it contains trace elements the roses need. For further information on fertilizing roses, visit

Inorganic fertilizers come in several choices: water soluble, granular and slow release. Apply a fertilizer with the appropriate three numbers; when in doubt, search online for the needs of specific plants. For example, 10-10-10 would encourage leaf growth in clematises when most gardeners want more blooms. A better ration in this case would be 1-2-1 (5-10-5) as roses benefit from more phosphorous than nitrogen.

Liquid fertilizers can give plants a much-needed boost whereas granular fertilizers can be harsh on young plants. Brushing back the mulch, apply the fertilizer around the drip line, not at the main stem as you want to feed the tips of the root system. It is always important to water well after applying the fertilizer.

For plants that bloom mid-summer to the onset of autumn, I always add a slow release fertilizer in the spring as most of these fertilizers will last for a good six months. Remember, there are plants that don’t need fertilizing. Prairie plants such as echinaceas and tough plants such as asters do just fine if the soil is decent.

Always remember that too much fertilizer is worse than not enough fertilizer. Fertilizing isn’t always easy. Indeed it can be time-consuming, but the heavy feeders, such as the roses and clematises will thank you for it.

Absent from their gardens, Kit and Lise enjoy roaming our region exploring the intersection of horticulture and suburban living. More on Instagram @AbsenteeGardener or email:

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