# VPD Chart vs Mars Hydro

The clearest difference is review sentiment: VPD Chart at 74% against Mars Hydro's 24%. VPD Chart also leads on rating (4.5 vs 2.6). Mars Hydro's advantage is in-app purchases (none vs 2). On price, ratings volume, update cadence and ads there is nothing between them.

Both are free to download. VPD Chart sells 2 in-app purchases, starting at $3.99 per month. Mars Hydro asks for nothing beyond the download.

VPD Chart holds the better App Store score, 4.5 against 2.6. Both are backed by a comparable volume of ratings — 30 and 27 respectively. Written reviews point the same way: 74% of VPD Chart's written reviews are positive against 24% of Mars Hydro's.

VPD Chart ships an update every 3 weeks, Mars Hydro monthly. The most recent releases landed on September 22, 2026 and August 11, 2026 respectively.

## The numbers

| Metric | VPD Chart | Mars Hydro |
| --- | --- | --- |
| Price | Free | Free |
| Rating | **[4.5 (30 ratings)](https://appshunter.io/ios/app/vpd-chart/id6470015847/reviews)** | [2.6 (27 ratings)](https://appshunter.io/ios/app/mars-hydro/id6479227564/reviews) |
| Number of ratings | **30** | 27 |
| Positive reviews | **73.7% of reviews** | 23.8% of reviews |
| In-app purchases | Yes | **No** |
| Ads | No | No |
| Update frequency | **Every 3 weeks** | Monthly |
| Monetization | Free with in-app purchases | **Free** |
| Size | 49 MB | 45 MB |
| Requires iOS | 15.1 | **15.0** |
| Devices | **iPhone, iPad, iPod** | iPhone, iPod |
| Age rating | 4+ | 4+ |
| Developer | [INNOVO DEV S.R.L.](https://appshunter.io/developer/1814828527) | [MARS TRADING RCC, INC.](https://appshunter.io/developer/1726858942) |

## What reviewers say

### VPD Chart

[App page](https://appshunter.io/ios/app/vpd-chart/id6470015847)

This app calculates Vapor Pressure Deficit (VPD) using air temperature, relative humidity, and canopy temperature. It offers real-time charting, sensor integration, and educational tools to understand plant growth environments. Organize data by zones and visualize dew point areas.

**Highlights:** VPD calculation, Interactive VPD chart, Sensor integration, Zone organization, Dew point visualization, Grow Timeline

**Features:** macOS Compatibility, Vision Pro support

**In-app purchases (2)**

| Purchase | Price | Billing |
| --- | --- | --- |
| VPD Chart Plus (monthly) | $3.99 | per month |
| VPD Chart Plus (annual) | $29.99 | per year |


### Mars Hydro

[App page](https://appshunter.io/ios/app/mars-hydro/id6479227564)

Control your smart grow system with this app. Manage LED lights, ventilation, and monitor environmental data like CO2, temperature, and humidity for optimal plant growth. Automate your entire grow kit to mimic natural conditions.

**Highlights:** LED light control with timers and simulation, Ventilation system management, Complete grow kit automation via iHub, Environmental data monitoring (CO2, temp, humidity, PPFD), Sunrise and sunset simulation

**In-app purchases:** none


## Frequently asked questions

### Is VPD Chart free?

VPD Chart is free to download, with in-app purchases available.

### Is Mars Hydro free?

Mars Hydro is free to download, with no in-app purchases.

### Which has better reviews, VPD Chart or Mars Hydro?

VPD Chart is rated higher. VPD Chart averages 4.5 out of 5 from 30 ratings, while Mars Hydro averages 2.6 from 27 ratings.

### Do VPD Chart or Mars Hydro have ads?

Neither VPD Chart nor Mars Hydro shows ads.

### Which is updated more often, VPD Chart or Mars Hydro?

VPD Chart ships an update every 3 weeks, and Mars Hydro monthly. Most recently, VPD Chart was updated on September 22, 2026 and Mars Hydro on August 11, 2026.

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*Compared by [AppsHunter](https://appshunter.io/) from daily US App Store data. Review summaries are generated from verbatim App Store reviews.*