Does plant growth’s 8 hour effect stack? [duplicate]

If you cast Plant Growth for its 8-hour version to

[…] enrich the land. All plants in a half-mile radius centered on a point within range become enriched for 1 year. The plants yield twice the normal amount of food when harvested.

and then come back the next day and cast it again the same way for the third time, would the total crops harvested be doubled, and then, quadrupled, and then octupled?
The campaign I am in is measured in years, so the impact of a druid (or in this case, nature cleric) who can spend 8 hours to double a 1/2 mile radius circle of food would be super helpful, but I need to know if I can prioritize one spot to make the growth exponential, vs going and casting in a different spot every day to just have a net double.

Is it possible to craft a crystal similar to the Truedeath one, but for creatures with the Plant type?

Is it possible to craft a crystal similar to the Truedeath one, but for Plants?

Truedeath Crystal (Greater) and Demolition Crystal (Greater) are Weapond Augment Crystals (Magic Item Compendium, p.65-66) that let you deliver critical hits and sneak attacks respectively to Undeads and Constructs.

To craft a Truedeath Crystal the Consacrate (Player’s Handbook v.3.5, p. 212) spell is required and Disintegrate (Player’s Handbook v.3.5, p. 222) has to be used to create a Demolition Crystal.

First question:

1. Which spell could be selected as prerequisite to craft a sort of Vinestrike* Crystal?

*similar to the Vine Strike (Spell Compendium, p. 230) spell


The other thing is: Lesser crystals have “unique” abilities, while Least and Greater seem to be standardized.

DEMOLITION CRYSTAL

[…]

Least: A weapon with this crystal attached deals an extra 1d6 points of damage to constructs.

Lesser: As the least crystal, and the weapon is treated as adamantine for the purpose of overcoming the damage reduction of constructs.

Greater: As the lesser crystal, and the weapon can deliver sneak attacks and critical hits against constructs as if they were living creatures.

and

TRUEDEATH CRYSTAL

[…]

Least: A weapon with this crystal attached deals an extra 1d6 points of damage to undead.

Lesser: As the least crystal, and the weapon also functions as a ghost touch weapon (DMG 224).

Greater: As the lesser crystal, and the weapon can deliver sneak attacks and critical hits against undead as if they were living creatures.

so:

2. What kind of ability a lesser crystal could grant?

How do Plant Growth and Slow interact with each other?

How do Plant Growth and Slow interact with each other?

If on spell-caster casts Plant Growth in an area and the other targets a creature with the Slow spell, what happens?

Supposing that the creature fails its saving throw against Slow would this mean that, while it is within the area affected by Plant Growth, its movement is two times, four times, or eight times slower?

I have got an inkling that the creature would only move 1 foot for every 8 feet of movement, but not sure is those two effects stack.

Thanks for your help with this.

Can you use a Glyph of Warding and Plant Growth to set up a semi-permanent effect in an area?

Can you use a Glyph of Warding and Plant Growth to set up a semi-permanent effect in an area?

Background

I am a Cleric/Druid in one of the campaigns I play in and the setting is an area with very little vegetation, bar some oases. Even then, the plants here have been suffering. So, I want to help the small settlements that are dotted about the area by using the permanent effect of Plant Growth.

This got me thinking about using the spell in conjunction with Glyph of Warding, to create a semi-permanent effect to really help these areas flourish and help the local villages in this region.

I want to cast Glyph of Warding in conjunction with the eight-hour version of Plant Growth, where I set a trigger of time, e.g. that one, or two, or three years have elapsed, and so forth. Would it be possible to set them up so that they trigger over a sequence of many years? Ideally, I want to be able to enrich the land of an area for 100 years. I could get other spell-casters to join me with this.

Is it possible to use Glyph of Warding and Plant Growth to set this up?

Thanks for your help with this.

Plant Growth

If you cast this spell over 8 hours, you enrich the land. All plants in a half-mile radius centered on a point within range become enriched for 1 year. The plants yield twice the normal amount of food when harvested.

(PHB p.266)

and

Glyph of Warding

Spell Glyph. You can store a prepared spell of 3rd level or lower in the glyph by casting it as part o f creating the glyph. The spell must target a single creature or an area. The spell being stored has no immediate effect when cast in this way. When the glyph is triggered, the stored spell is cast. If the spell has a target, it targets the creature that triggered the glyph. If the spell affects an area, the area is centered on that creature. If the spell summons hostile creatures or creates harmful objects or traps, they appear as close as possible to the intruder and attack it. If the spell requires concentration, it lasts until the end o f its full duration.

(PHB pp. 245-246)