Grow & Tell is IPR’s biweekly gardening segment to guide you through the growing season. In each episode, I’ll walk you through gardening tasks tailored for northern Michigan’s climate and soils — whether you're working with raised beds or patio pots.
Have gardening questions you want Grow & Tell to answer? Email me at dylan.kulik@interlochen.org.
Today’s tip: Give your tomatoes a nutrient boost — through their leaves
We’re back in the tomato garden today, and some of my plants are looking a little yellow and sad.
If you’ve planted your tomatoes in a container or garden bed, you’ve already given them a solid start. But maybe you don't have the space or time to add compost — still, your plants might need a little extra help to thrive.
Luckily, there's something we can add to the green stems and leaves of the plant to give it an extra boost: foliar nutrients.
Two seasons, two sets of needs
Tomatoes grow in two distinct phases:
- Early season (late May to late July): This is when your tomato plants are focused on growing tall, developing lots of stems and leaves. During this phase, they crave nitrogen.
- Late season (August through harvest): Once flowering and fruiting begin, tomatoes shift their energy to producing blossoms, buds and fruit — and need more calcium, magnesium and sulfur.
Why feed the leaves?
Instead of feeding the roots, foliar nutrition delivers nutrients directly to the plant’s stems and leaves. This is especially helpful for container-grown tomatoes that don’t have access to the deep, nutrient-rich soil of an in-ground bed. Plus, leaves can take up nutrition a lot more quickly than roots can.
On the underside of every leaf are tiny pores called stomata, which open and close daily. When open, they can absorb water and nutrients sprayed directly onto the leaf surface.
Step 1: Gather your foliar nutrients
Today, I'm grabbing these from the shed. You can find them online or at your local garden store.
- Fish and kelp emulsion (rich in nitrogen — great for early growth)
- Solution-grade gypsum (for calcium and sulfur — ideal later in the season)
- Langbeinite (adds magnesium and potassium — for flowering and fruit set)
For now, I’m just using the fish and kelp blend, since we’re still early in the season.
Step 2: Mix and apply
Grab a clean spray bottle and follow the dilution instructions on the product label — whatever you buy, you'll want to mix the nutrient with warm water. Shake it up really well, then spray the tomato plant top to bottom.
✅ Focus especially on the underside of the leaves
✅ Apply early in the morning, ideally around 8 a.m.
🚫 Avoid hot, dry afternoons or evening sprays — the stomata will be closed
Why this works
This method goes out to my container gardeners: foliar nutrient application gives you flexibility in confined spaces or when you have limited soil nutrition. Even if your roots are maxed out, the leaves can keep feeding the plant.
Foliar feeding is quick, effective and can help your plants grow stronger and more productive. Plus, it's a fun way to spend some more time with your tomatoes.
Foliar Feeding Takeaways 🍅
- Use fish and kelp emulsion for nitrogen in the early season
- Spray early in the morning when stomata are open
- Focus on the undersides of the leaves
- Try gypsum and langbeinite in the fruiting and flowering phase
- Especially useful for potted tomato plants
Have some fun with it — experiment, observe and see how your plants respond! Happy gardening!
