Can I Use Tomato Feed On Hydrangeas

If you’re a gardener with both tomatoes and hydrangeas, you might look at a bottle of tomato feed and wonder, can I use tomato feed on hydrangeas? It’s a smart question, as re-purposing plant food can save time and money. The short answer is yes, you can, but with some very important caveats. Using the wrong fertilizer, or using the right one incorrectly, can lead to disappointing blooms or even harm your plants.

Tomato feed is a type of fertilizer specifically formualted for fruiting plants like tomatoes, peppers, and cucumbers. It’s typically high in potassium (the third number on the fertilizer label, like 4-5-8). Potassium promotes flower and fruit development. Hydrangeas, especially the big-leaf varieties (Hydrangea macrophylla), are grown primarily for their stunning floral displays. So on the surface, a potassium boost sounds good, right?

The issue lies in the other two numbers on the label: nitrogen (first number) and phosphorus (second number). Tomato feeds are often lower in nitrogen to prevent excessive leafy growth at the expense of fruit. More crucially, many are high in phosphorus. This is where we hit the first major snag for hydrangeas.

The Big Problem: Phosphorus and Blue Hydrangeas

If you have blue or purple hydrangeas, their color depends on the availability of aluminum in the soil, which the plant can uptake only in acidic conditions. High levels of phosphorus in the soil chemically binds with aluminum, making it unavailable to the plant. This can cause your vibrant blue hydrangeas to turn pink or a muddy, washed-out color.

For blue hydrangeas: Using a high-phosphorus tomato feed regularly can permanently alter flower color by locking up aluminum.
For pink/red hydrangeas: Phosphorus is less of a direct issue for color, but an imbalance in nutrients still isn’t ideal.

Nutrient Balance: What Hydrangeas Really Need

Hydrangeas benefit from a more balanced fertilizer or one tailored to their needs. A general-purpose fertilizer like a 10-10-10 or one labeled for trees and shrubs is often safer than a specialized tomato formula. Their main requirement is for consistent moisture and good soil organic matter, not necessarily heavy feeding.

Nitrogen (N): Supports green, leafy growth. Too much leads to lots of leaves and few blooms.
Phosphorus (P): Supports root and bloom development. Often already sufficient in garden soils.
Potassium (K): Supports overall plant health, disease resistance, and bloom quality. This is the beneficial part of tomato feed.

When You Might Consider Using Tomato Feed

There are a couple scenarios where using leftover tomato feed on hydrangeas isn’t a terrible idea.

As a one-time, mid-summer booster: If your hydrangea is budded up and you want to support the size and longevity of the blooms, a single, diluted application of tomato feed can provide that potassium kick. Do this only after the plant is already forming buds.
On established, pink or white varieties: For hydrangeas where color isn’t tied to soil aluminum (like pink mopheads, oakleaf, or panicle hydrangeas), the risks are lower. The nutrient imbalance is still a minor concern, but less dire than for blues.

Step-by-Step: How to Safely Use Tomato Feed on Hydrangeas

If you decide to proceed, follow these steps to minimize risk.

Check the Fertilizer Label: Look at the N-P-K ratio. If the middle number (Phosphorus) is the highest (e.g., 3-8-5), avoid it, especially for blue hydrangeas. If it’s more balanced or high-potassium (e.g., 4-5-8), it’s a better candidate.
Dilute More Than Recommended: If the label says 1 cap per gallon, use ½ a cap. This reduces the strength of all nutrients, including the problematic phosphorus.
Apply to Damp Soil: Never fertilize a dry plant. Water the hydrangea thoroughly a few hours before applying the feed to prevent root burn.
Apply at the Right Time: The best time is early to mid-summer, just as flower buds are swelling. Avoid early spring (needs balanced growth) and late summer/fall (can promote tender growth that winter kills).
Water it In Well: After applying the diluted feed, water again gently to help move the nutrients into the root zone.

A Better Approach: Fertilizers Made for Hydrangeas

For consistent results and heathier plants, it’s best to use products formulated for acid-loving plants or hydrangeas specifically.

For Blue Hydrangeas: Use a fertilizer for acid-loving plants (like azalea/camellia food) or one with added aluminum sulfate. These are low in phosphorus.
For All Hydrangeas: A slow-release, balanced shrub fertilizer applied once in spring is often perfect. It feeds the plant gently over months.
The Organic Route: Amending soil with compost, well-rotted manure, or cottonseed meal provides a gentle, balanced nutrient source and improves soil structure. This is often all your hydrangeas need.

Common Signs of Fertilizer Problems

Keep an eye on your hydrangeas after any feeding. If you notice these signs, you may need to adjust your practice.

Lush leaves, no flowers: Too much nitrogen. This is a common result of using the wrong fertilizer type.
Burnt leaf edges: Root burn from over-application or applying to dry soil.
Color change in blooms: As discussed, high phosphorus can shift blue flowers toward pink.
Weak, spindly growth: Could indicate a lack of balanced nutrients or over-reliance on one type of feed.

Essential Hydrangea Care Beyond Feeding

Remember, fertilizer is just one piece of the puzzle. Proper care is more important than any feed.

Watering: Hydrangeas need consistent moisture, especially in heat. Their name comes from “hydra.” Deep watering is better than frequent sprinkles.
Sunlight: Most prefer morning sun and afternoon shade. Too much shade reduces flowering.
Pruning: Know your type! Big-leaf hydrangeas bloom on old wood. Pruning at the wrong time removes next year’s flowers. Panicle and smooth hydrangeas bloom on new wood.
Soil pH: Test your soil. For blue flowers, aim for a pH of 5.2-5.5. For pink, aim for 6.0-6.2.

FAQ: Tomato Feed and Hydrangeas

Can I use tomato feed on all hydrangeas?

It’s riskier for blue hydrangeas due to phosphorus content. For white hydrangeas like panicle types (Hydrangea paniculata) or oakleaf hydrangeas, the risk is lower, but a balanced feed is still preferable.

What is the best fertilizer for hydrangeas to bloom?

A balanced, slow-release fertilizer (like a 10-10-10) applied in early spring or a fertilizer labeled for acid-loving plants is ideal. Avoid high-nitrogen lawn fertilizers nearby, as runoff can effect flowering.

How often should you feed hydrangeas?

Once in early spring is often enough, especially if you use a slow-release formula or have rich soil. A second, light feeding in early summer can be beneficial for some types, but overfeeding is a common mistake.

Does tomato feed change hydrangea color?

Yes, it can. The phosphorus in many tomato feeds can prevent blue hydrangeas from accessing aluminum, leading to pinker flowers. It doesn’t affect the color of white hydrangeas.

Is tomato feed good for other shrubs?

It can be used cautiously on other flowering shrubs that benefit from potassium, like roses. However, always check for specific needs, as some shrubs may be sensitive to the nutrient balance. Its really best saved for your vegetables.

In conclusion, while you technically can use tomato feed on hydrangeas in a pinch, it’s not the best practice for long-term plant health and optimal blooms. The potential for nutrient imbalance and color alteration, especially for prized blue hydrangeas, makes it a gamble. Investing in a appropriate, balanced fertilizer or simply enriching your soil with compost will give you healthier plants and more reliable, vibrant displays year after year. Sometimes, its best to let tomato feed do it’s intended job and give your hydrangeas what they truly need.