Slow-Release or Water-Soluble: The Best Fertilizer for the Job

One of the most common questions I hear from customers at the nursery is, "Which fertilizer should I use?" Annuals, shrubs, perennials, trees--all plants need proper nutrients to keep growing and looking their best. So why the confusion?

The fact is, you could probably go shopping for fertilizer and end up with a different product for each and every one of your plants. Discouraged by so many choices, many people end up choosing the easiest-sounding option: slow-release fertilizer. Feed once for the season and you're done. Sounds good!

But not so fast. Slow-release fertilizers, while great for many plants, may not be the best for what you need to feed. Annual flowers--especially hanging baskets--really need more nutrients than a slow-release fertilizer can provide at any one time. At Vander Giessen Nursery, our custom-blended potting soil has a slow-release fertilizer added--for the first month or so after planting our beautiful Lynden Baskets, we can rely on it to feed the young plant starts. After no more than six weeks, however, we need to start supplementing that with water-soluble fertilizer. The same is true for any annuals you plant--slow-release may be a good way to start, but don't rely on it exclusively.

Here's a good rule of thumb: if you wish to use slow-release fertilizer on your flowers, do so--but continue to feed with water-soluble fertilizer at half the recommended dose. That way your flowers will get the added boost on a regular basis while also benefiting from sustained release of nutrients in the event you forget to fertilize for a week or two.

So, then, which water-soluble fertilizer is best? Miracle-Gro is the most common, but as you may have heard us recommend, Jack's Classic is far better. Here's a quick breakdown of the different blends of Jack's Classic available:

• All-Purpose: Great for balanced growth and blooming on annuals. Also an excellent fertilizer for vegetables. Use weekly.
• Blossom Booster: True to its name, excellent for encouraging more blooms. Alternate weekly with All-Purpose for increased flowers and continued plant growth.
• Petunia FeED: Best option for petunias, calibrachoa ("Million Bells"), and bacopa. Added iron helps keep these plants from developing yellow leaves or becoming weak and spindly. Use any time, but be sure to start by mid-summer, alternating with All-Purpose and Blossom Booster as needed.  

Please note, there are no real "rules" to using these fertilizers--if you think your flowers need to bloom more, use the Blossom Booster blend for two or three weeks in a row. Likewise, All-Purpose may be used at any time for more growth, and Petunia FeEd can be used exclusively throughout the season. These are simply our recommendations based on the results we've seen. 

Now, for shrubs, trees, and perennials, slow-release fertilizers are a great option to provide season-long feeding. Osmocote is the most popular brand, but at Vander Giessen's, we like Jack's Classicote better--it does the same thing as Osmocote, just better. Another great slow-release option from Jack's is called Crystal Green. Made with nitrogen derived from waste water treatment plants, it's completely sustainable and helps to keep nitrogen from being released into our waterways. Either of these options would be great for your plants.

Ultimately, your plants will only be as great as the care they receive, and while understanding the best fertilizer for the job may take a little bit of work, the rewards of healthier, longer-lasting plants will be well worth the effort. If you have further questions, we're here to help!